CA1219911A - Tracing electrical conductors by high-frequency loading and improved signal detection - Google Patents
Tracing electrical conductors by high-frequency loading and improved signal detectionInfo
- Publication number
- CA1219911A CA1219911A CA000449772A CA449772A CA1219911A CA 1219911 A CA1219911 A CA 1219911A CA 000449772 A CA000449772 A CA 000449772A CA 449772 A CA449772 A CA 449772A CA 1219911 A CA1219911 A CA 1219911A
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- time period
- predetermined
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- conductor
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Abstract
Abstract Tracing and identifying electrical conductors in a power distribution network is achieved by use of a transmitter operating on a duty cycle of absorbing current pulses at a predetermined frequency from the power distribution network, and by use of a remotely located receiver which detects the electromagnetic field signals resulting from the current pulses in a predeterrmined cyclic manner of operation defined by a sample period and a reset period. During the sample period the receiver supplies an indication of the maximum received strength of the transmitter signal. The relationship of the duty cycle of the transmitter and the sampling and reset periods of the receiver reduce the potentially adverse influences of spurious signals on the receiver.
Description
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TRACING ELECTRI~AL CONDUC'TORS BY
HIGH-FREQUENCY LOADING AND IMPROVED SIGNAL DETECTION
Background This invention relates to new an~ improve~ appara-tus and methods for tracing electrical conductors of both alte~nating and direct current electrical power, and more specifically it pertains to identifying circuit breakers, fwses, switches and other current conducting or handling devices connected to a source of electrical power.
It is oftentimes necessary to trace and identify particular cixcuits and electrical devices in a power distribution network, such as circuit breakers or fuses. Identification has typically been accomplished by practicing one or two manual techniques. One technique is to selectively disrupt power by opening the circuit breakers one at a time. When power is no longer present at the circuit, electrical device or feeder conductor in question, the opened circuit breaker identifies the item in question. The disadvantage to this technique is that electrical power is temporarily disconnected Erom each of the circuits and branch conductors in the course oE the search, and it may be critical to maintain power to some o~ these circuits and branch conductors. Critical circuits include those which supply power to hospital equipment, computers, and many other types of sensitive electronic equipment. Another disadvantage is that a considerable amount of time is consumed in selectively and individually opening each of the circuit breakers. The second manual technique of identifying a circuit breaker is to introduce a sufficiently high electrical current load on the particular branch conductor to trip the circuit breaker or open the ~,..
,~
9~
fuse. This technique is typically achieved by introducing an intentional short circuit to the branch conduc-tor. l'he disadvantage of this technique is -that the power will then be totally disrupted, crea-ting the detrimental consequences previously mentioned. The increased curren-t drawn by the short circuit can create dangerous ~omentary overheatiny or fire conditions or can cause larger trunk or distribution breakers to trip open at the same time the branch circuit breaker is tripped open. Of course, once a distribution breaker trips open, a large number of branch and distribution conductors will be disconnected from the source of electrical power.
A variety of test instruments are also available for testing and determining a variety of different electrical conditions including tracing and identifying feeder conductors, circuit breakers and other current conducting devices as well as tracing and identifying short circuited conductors.
Certain of these prior art devices require interruption of power to -the conductors in order to accomplish the tracing 20 an~ identification. Other types of prior art devices employ means which cyclically create a current load on a particular conductor of sufficient magnitude to allow the increased current load, and hence the electrical device, to be identified wi-th a conventional ammeter or impedence measuring device.
Still other types of prior art devices introduce a relatively high-frequency signal on the conductor while conventional power is maintained and high-frequency signal is inductively detected. The high-frequency signal detection apparatus offers the best potential for reliable and simple circuit identification and detection, but such prior art devices are ~z~9~
typically subject to adverse and detrimental influences, such as false signals resulting from spurious signals Eron transients and switching currents, reduced sensitivi-ty for detecting and identifying the desired feeder condùc-tors through panel enclosures and tubular conduits, and a somewhat limited specificity in isolatiny one particular corlductor from a number of other conductors loca-ted in close proximity.
Other disadvantages of such prior art systems and methods are known to those appreciating this particular field and its problems, and will be made more particularly apparent with comprehension of -the desirable features of the presen-t invention.
.3_ 12~
Summary It is the general objective of this invention to provide a new and improved apparatus and method :Eor tracing and identifying electrical conduc-to:rs whlch eY~h:ib:it-, a relatively high imrnuni-ty to adver~e influences frvm spllr:ious signals such as transients and switching currents, which does no-t require the interrup-tion of applied power duri.ng the testing and tracing procedures, which exhibits a relatively high sensitivity and selec-tivity for more precisely identifying the particular electrical circuit conductor out of a closely assembled group without disassembly of various housings and enclosures containing the feeder conductor, and which is rendered substantially insensitive to different magni-tudes of voltage applied over the power distribution network.
In accordance with the present invention, there is provided an apparatus for tracing and identifying an electrical current carrying conduc-tor or similar means which is energized and is carrying current therethrough at a power frequency. The apparatus comprises, in combination, transmitter means and receiver means. The -transmitter means is adapted for connection tO -the conductor for drawing electrical current from the energized conductor in repetitious transmission duty cycles, each transmission duty cycle being a predetermined waveform having a -first predetermined time period during which a plurallty of current pulses are drawn from the energized conductor at a predetermined frequency and a seconcl predetermined time period during which no current is drawn .Erom -the conduc-tor.
The current pulses drawn during the first predetermined time period are suEficient to induce about the conductor a predetermined electromagnetic field having a frequency charac-teristic corresponding to the prefletermined :Erequency of the current pulses drawn duxing the first predetermined -time period. The predetermined Erequency is so substantially different from -the power freqwency a-t which current is otherwise conducted that the detection o~ the predetermined electromagnetic Eield a-t a predetermined ~requency i~
substantially independerlt of the magnitude oE the current otherwlse conducted by the energi~ed conductor relati~e -to the magnitude of -the current pulses drawn by the transmi-tter means. The receiver means is operative when positioned in relation to the conductor for detecting the frequency characteristic and determining the strength of the predetermined electromagnetic field induced by the curren-t pulses during the first predetermined -time period by the transmitter means. The receiver means also includes means for indicating the relative strength of the predetermined electromagnetic field at the predetermined frequency.
The inven-tlon itself is more precisely defined by the appended claims. The improvements and concepts from the presen-t invention are more specifically de~cribed in the accompanying description of the preEerred embodiments takerl in conjunction with the drawings.
Drawings FIG. 1 is a generalized and schema-tic view of a transmitter and a receiver o~ the present in~ention illustra-ted in conjunction with a schematic electrical power distrib~-tion networ'~.
FIG. 2 is a schematic diagram of one em~odimen-t of the transmitter shown in E'IG. 1.
FIGS. 3A, 3B, 3C, 3D, 3E, 3F, 3G, 3H and 3I are waveform diagrams illustrating the operation of the transmitter shown in FIG. 20 FIG. 4 is a schematic view of one embodiment of the receiver shown in FIG. 1.
FIG. 5 is a waveform diagram utilizing the same time reference as employed in FIGS. 3A to 3I, illustrating the operation of the receiver shown in FIG. 4.
FIG. 6 is a schematic di.agram of an alternative portion of the receiver shown in FIG. 4.
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Pre~erred Embodiments The two basic components of the presen-t inven-tion are a transmitter 10 and a receiver 12 shown in FIG. 1. The transmitter 10 is electrically connected in-to a power distribution network through which electrical power is supplied, as by connecting a plug prony 14 of the -transmi-t-ter 10 into a convenience outlet 16l for example. The convenience outlet 16 is electrically connected to a branch line or conductor 18 extending from a load center 20. Other branch lines, e.g. 22 and 24, also extend from the load center 20 and are connected with other elements such as additional convenience outlets 16a and 16b. Electrical power is supplied to the branch conductors 18, 22 and 24 through branch circuit breakers 26, 28 and 30, respectively, which are located within the load center 20. Neutral conductors 32 return current flow from the branch conductors 18, 22 and 24 to -the load center at a neutral bus 34. Electrical power is supplied to the load center 20 from a secondary line transformer 36, a plurality of feeder conductors 38, a plurality of main distribution breakers 40 and a plurality of distribution collductors 42 of the power distribution network, as is typical. A ground conductor 44 also extends through the power distribution network between the secondary line transformer 36 and each neutral bus 34. The branch circuit breakers 26, 28 and 30 protect the branch conductors 18, 22 and 24, respectively, from current overload conditions by trippin~ open upon the occurrence of an increased current drawn through any one of the branch lines. Similarly, the main distribution breakers 40 protect the distribution conductors 42 from current overload conditions.
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The transmitter 10 receives electrical power from one of the branch conductors, e.g. 18, and draws or absorbs current from that particular branch line in a prede-terMined pattern or waveEorm. The predetermined pat-tern or curren-t waveform drawn from the particular branch conduc-tor to which the transmitter is connec-ted induces a predetermined electromagnetic field directly rela-ted to the current waveform. The electromagnetic field extends along all of the branch conductors and each of the elec-trical devices operatively connected with these conduc-tors. For example, when the transmitter 10 is connec-ted into the branch conductor 18, the electromagnetic field is present at the branch conductor 18, the branch circuit breaker 26, and at one of -the distribution conductors 42 and main distribution circuit breakers 40 and feeder conduc-tors 38 electrically connected to the branch line circuit breaker 26 and over the neutral conductor 32.
The receiver 12 includes an electromagnetic field transducer means positioned at the distal end of a probe 46.
The receiver 12 operatively senses the strength of the predetermined electromagnetic field, rejects substantially all other signals and operatively indicates the strength of the electromagnetic field by lighting one of a plurality of indi.cators 48. In this manner, branch conductors, electrical devices connected to the branch conductors, branch circuit breakers, dis-tribution conductors, main distribution breakers, the feeder conductors and the neutral conduc-tors can be traced and identified without interrupting the supply of power from the power distribution network.
Idcntification proceeds by placing the transducer means of the probe 46 adjacent each of the electrical devices ~2~9~
in question and noting the field strength indication on the indicators 48 with respect to each. The par-ticular electrical device exhibiting the greatest field streny-th lndi.ca-tion is the device identified. As will become more apparen-t, the nature and operation o:E each transmit-ter 10 and receiver 12 provide an imp:roved capability for traciny and i~entifying electrical devices.
One embodiment 10' of the transmitter 10 is better understood by reference to FIGS. 2 and 3A to 3I. As shown in FIG. 2, the transmitter 10' comprises a power supply circuit 50, a duty cycle controller 52, a gated oscillator 54, a driver circuit 56, and an output circuit 58. The power supply circuit 50 generally draws applied AC or DC power from the power distribution network through the plug prongs 14.
Alternating current power is rectified by a full wave rectifier 60 and pulsating direct current power (FIG. 3G) is applied on conductor 62 to a conventional integrating and regulating circuit comprising a transistor 64, a Zener diode 66, a capacitor 68, and the resistors 70 and 72.
Regulated DC power is thereby present on terminal 74 and is conducted to other active components of the elements 52, 54, 56 and 58 of the transmitter 10'.
In the duty cycle controller 52, a pair of capacitors 76 and 78 are electrically connected in series between the terminal 74 and a ground reference 80. The input terminal to an inverting Schmitt trigger 82 is connected to the terminal 3A between capacitors 76 and 78. The output terminal 3B of the Schmitt trigger 82 is connected to the input terminal 3A through a parallel-branch feedback network comprising resistors 84 and 86 and a diode 88. The ~9~
capacitors 76 and 78, the resistors 84 and 86, and the diode 88, in conjunction with the Schmit-t trigger 82, form a resistive capacitive timing network of the du-ty cycle controller.
Capacitors 76 and 78 charye and discharge at terminal 3A in accordance with the waveform diagram shown in FIG. 3A. The output waveform from the Schmit-~ triyger 82 at terrQinal 3B
is illustrated in FIG. 3B. Accordingly, the two time periods established by the timing network, as shown in FIGS. 3A and 3B: a considerably longer off-time period 89, for example approximately 900 milliseconds, and a considerably shorter on-time period 91, for example approximately 45 milliseconds.
The ratio of the on-time period 91 to the off-time period 89 is controlled by the ratio of the sum of the resistances of resistors 8~ and 86 to the resistance of the resistor 84.
The on-time period 91 and the off-time period 89 are controlled by the values of the resistors 84 and 86 in relation to the values of capacitors 76 and 78. The diode 88 operatively connects the resistor 86 in the feedback path of Schmitt trigger 82 during the on-time period 91 but eliminates the ~o resistor 86 from -the feedback path during the off-time period 89.
The sated oscillator 54 is operative during the on-time period 91 when a diode 90 connected between terminal 3B and an input terminal 3C of an inverting Schmitt trigger 92 ~5 is not conductive. A capacitor 94 is connected between terminal 3C and the ground reference 80. A resistive feedback path defined by resistor 96 and potentiometer 98 is connected between an output terminal ~D of the Schmitt trigger 92 and its input terminal ~C. When the potential of the signal at terminal 3B attains its minimum level during the off-time period 89, the diode 90 is conductive. The voltage increases on capacitor 94 until the trip point of the Schmitt trigger 92 is attained. At the trip point, the resistive feedbac~ path of the resistor 96 and potentiometer 98 in conjunction with the capacitor 94 causes the Schmitt trigger 92 ~o oscillate at a frequency established by the valu~s of the elements 9~, 9~ and 98, for example about 6 kH~. The frequency of oscilla-tion can be adjusted by varying the resistance of the potentiometer 98.
The oscillation occurring durin~ the on-time period 91 is illustrated in FIGS. 3C and 3D, with FIG. 3C illustrating the input signal at terminal 3C and FIG. 3D illustrating the output signal at terminal 3D from the Schmitt trigger 92.
Four parallel-connected, inverting Schmitt triggers 100, 102, 104 and 106 primarily define the driver circuit 56.
15 The Schmitt triggers 100, 102, 104 and 106 receive as an input signal the signal at terminal 3D shown in FIG. 3D.
The Schmitt triggers of the driver circuit 56 provide added current to drive a transistor 108 of the output circuit 58.
The waveform at the common output terminal 3E of the Schmitt 20 triggers 100, 102, 104 and 106 is shown in FIG. 3E.
The output circuit 58 draws high freqency alternating current from the power distribution network when the transistor 108 is conductive. Of course, the transistor 108 conducts in accordance with the alternating high frequency current established during the on-time period 91 of the waveform, shown in FIG. 3E. When conductive, the transistor 108 operatively connects resistors 110 and 112 between the conductor 62 and the ground reference 80. Since the transistor 108 conducts in accordance with its input signal (FIG. 3E) during the on-time period 91, a high frequency current is conducted through resistors 110 and 112 as shown by the current waveform in FIG. 3H. FIG. 3G illustrates -the voltage waveform present on conductor 62 and at termina] 3G. A gas indicator bulb 114 lights during the time periods tha-t the transistor 108 is conductive and indica-tes -the opera-tion of the transmitter 10.
The high frequency rectified curren-t load:iny shown in FIG. 3H is conducted Erom the full wave rectifier 60 over conductors 115 and 116 to the pronged plug 14, as the alternating waveform shown in FIG. 3I. A varistor 118, is connected between conductors 115 and 116 to protect the transmitter 10 from overvoltage conditions due to voltage transients, lightning and inductive spikes and the like and from possible improper use. A fuse 120 is connected in the conductor 116 to protect the transmitter from excessive currents.
One of the significant advantages of conducting a high frequency current loading signal from the power distribution network in the duty cycle established by the on and off time periods 91 and 89 respectively, is that the high-frequency current-conducting transistor 108 does not experience ~0 excessive heating. The extent of heating of the transistor is related to the square of the voltage at the plug prong 14 during the time when the transmitter is conductive. In a practical embodiment, the transistor 108 can conduct as much as one amp of current which, during the time the transistor is conductive, results in significant heat creation. However, by operating with a duty cycle having a significantly long off-time period 89 as compared to the on-time period 91, the average effect of the heating is greatly reduced. The relatively large current conducted during the on-time period creates an electromagnetic field of sufficient strength ~9~
-to be reliably detected at significantly remote locations along the conductors within the power distribu-t~on network.
By not operating with a duty cycle characteristic, the strength of the field would be subs-tantially reduced, or relatively expensive and additional components would be - required to obtain comparable field s-tren~th~ A~cordinyly, the number and cost of the elements in the transmitter is reduced, the life of the transistor 108 is prolonged and -the reliability of the transmitter is enhanced.
One embodiment 12' of the receiver 12 is better understood by reference to FIG. 4. The receiver 12l includes a transducer means 122, a filter section 124, a variable gain section 126, an indicator section 128, a peak detector 130, a level indicator 132, and a reset section 134 operatively connected together. In addition, the receiver 12' includes a ground reference section 136 for maintaining the voltage reference levels of the elements of the receiver 12l.
The receiver 12' receives energy from self-contained batteries 140 and 142 of -the ground reference sec-tion 136.
The battery 140 is electrically connected be-tween terminals 146 and 148 to operatively establish a positive vol-tage level on teLminal 146 and a negative voltage level on terminal 148. The positive and negative voltage levels at terminals 146 and 148, respectively, are equally spaced above and below ~5 ground reference 144 and are maintained in the equally spaced relationship by the operational amplifier 150, the resistors 152 and 154 ancl the capacitor 156 connected in a known operative arrangement.
The transducer 122 is of the inductive type and utili~es an inductor or coil 160. A capacitor 162 is connected ~23 9~
in parallel relationship with the inductor 160, and the capacitor-inductor combina-tion is a -tuned or resonant clrcui-t with a resonant frequency equal to -t~e frequency o~ -the curren-t loading pulses delivered by the transmi-tter 10 during -the on-time period 91. A resistor 164 is connected between the coil 160 and capacitor 162 and the inver-ting input terminal of an operational amplifier 166. The reslstor 16~ reduces the effects of ringing in the tuned circuit 160 and 162 which may occur as a result of high-frequency transients that appear randomly and spuriously on the conductors of the power distribution network. A feedback loop defined by a capacitor 168 and resistor 170 is connected between the output terminal of the operational amplifier 166 and its input terminal. The values of elements 164, 168 and 170 establish the operational amplifier 166 as a lo~ gain, low pass frequency amplifier. Accordingly, the signal inductively received by the tuned circuit 160 and 162 is amplified to a magnitude well within the range between the positive and the nega-tive voltage supply levels established by the ground reference section 136. The values of the elements 16~, 166, 168 and 170 also operatively establish a roll-off frequency point, for example about 35 kHz, at a frequency substantially higher than the high-frequency signal from the transmitter 10 but substantially less than the major high-frequency components of voltage transients and spikes. A very flat gain response is thereby obtained between -the frequency of the transmitter signal and the power line frequency, typically 60 Hz. Consequently, the power line frequency will not be amplified more than the transmitter signal frequency, and the high frequency transients and spikes will be attenuated.
The filter section 124 basically comprises three serially connected filter means, 172, 174 and 176. Each of the filter means 172, 174 and 176 is an iden-tical Sallen-Key band-pass filter of well-known circuit configura-tion. The component values of each Sallen-Key band-pass Eil-ter are selected to provide a low Q for each individual filter, for example approximately two. As is well known, a Q is one measure of the ability of a band-pass filter to pass a particular range of frequencies. One definition of Q is the center frequency of the band pass filter divided by the frequency band width which the filter passes. Band-pass filters with high Q's are more susceptible to ringing than band-pass filters of lower Q's. During ringing a band-pass filter is rendered inoperative for its intended purpose. By placing three relatively low Q filters in series, the total Q of the filter section 124 for band-pass purposes is the sum of the Qs of each filter. For example, if each of the filters 172, 174 and 176 has an individual Q of two, the to-tal Q of the filter section 124 is approximately six with respect to filtering the desired signal. The ability of the filter section 124 to withstand the effects of ringing from high-frequency transients is not related to i-ts total Q, as it would be in the case of a single high Q filter. Instead, the ability to withstand ringing in the filter section 124 is related to the ability of one of the filters 172, 174 or 176 to withstand the potential for ringing. As an important result, the filter section 124 is highly selective in passing only the transmitter signal but is not highly susceptible to ringing. Accordingly, the signal present on conductor 178 is essentially a signal directed related -to the high-frequency 'I '~ "
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current loading created by the transmitter 10. The alternating power frequency has been selectively removed by the operational effects of the Sallen-Key fi].ter means 172, 174 and 176. In addition, the effects of high-frequencies have been siynifican-tly attenuated by the coil 160 and capaci.tor 162, and by -the resistive capacitive network of elemen-ts 164, 168 an~ 170.
The three Sallen-Key band pass filter means 172, 174 and 176 even further isolate and supply the signal created by the transmitter 10.
The signal available on conductor 178 is general].y referenced positively with respect to ground 144. The positive reference results because each of the operational amplifiers of the Sallen-Key band-pass filters 172, 174 and 176 are referenced directly to ground 144 without current offsets.
It is the general function of the variable gain section 126 to amplify the signal on conductor 178 and to reference that signal midway between the positive and negative voltage levels at terminals 146 and 148. The signal on conductor 178 is applied through a potentiometer 180 and a resistor 182 to the inverting input of an operational amplifier 184. A feedback network comprising resistors 186, 188 and 190 and a multiposition switch 192 is provided to adjust the gain of the operational amplifier 184. By positioning the switch 192 in one of its three positions, one or more of the resistors 186, 188 and 190 is connected in the feedback network to control the gain. The various stages of gain provided by the feedback network accommodate different strengths of signals detected. It is apparent that the high-frequency current drawn by the transmitter 10 induces a -17~
signal strength in the conductors which diminishes in accor-lance with the length over which the signal is conduc-ted, the number of elements through which the signal mus-t be conduc-ted and the presence of an exterior shieldiny enclosure. The highest gain available is when the switch 192 i~ open an~
all resistors 186, 188 and 190 are connected in -the fee~back loop~ The highest level of gain is desirable for identlfying current carrying devices i.n panel boxes or distribution or feeder conductors. In the medium gain setting, where resistors 186 and 190 are connected in the feedback loop, the gain is generally sufficient for tracing and identifying circuit breakers and switches. The low stage of gain, when switch 192 connects only resistor 186 in the feedback loop, is useful for detecting accessible branch conductors, for example.
With the appropriate level of gain established, the signal supplied from the output terminal of the operational amplifier 184 is supplied to an inverting input terminal of an operational amplifier 194 of the indica-tor section 128.
The current supplied from the operational amplifier 194 drives ~0 a piezoelectric speaker 196. The speaker 196 supplies an audio signal at the frequency of the current loading signal from the transmitter 10, for example 6 kHz. This frequency of the transmitter signal is easily audibly perceived by the user as an assurance of proper identification and use of the transmitter 10 and receiver 12.
Feedback from the output terminal of the operational amplifier 194 is conducted from the audio indicator section 128 through a resistor 198 to the noninverting input of the operational amplifier 184 of the variable gain section 126.
A capacitor 200 charges to the center level of the signal ~9~
clelivered from the operation amplifier 194. Since the operational amplifiers 184 and 194 each invert their inpu-t signals, the signal presen-t on capaci-tor 200 i.s essentially of the same polarity as the average center level of -the signal supplied to the inver-ting input term.inal of the operational amplifier 184. AccordincJly, the signal supplied at the output terminal of the opera-tional amplifier 184 is centered with respect to the ground reference 144 and this signal is applied on conductor 202 to the peak detector section 130.
In the peak detector 130, the signal on conductor 202 passes through capacitor 204 which, in conjunction with resistor 206, changes the level of the signal on conductor 202 from being referenced to the ground reference 14~ to being referenced to the negative voltage level at terminal 148.
A resistor 208 is connected between the noninverting input of an operational amplifier 210 and the capacitor 204. The resistor 208 prevents current from being drawn from the capacitor 204 when the voltage on the capacitor 204 swings ~0 below the negative voltage level at terminal 148 on every other half cycle of the signal on conductor 202. Output current delivered from the output terminal of the operational amplifier 210 is conducted through a resistor 212, a diode 214 to a capacitor 216. As will become more apparent, the capacitor 216 is normally maintained in a discharged condition with respect to the nega-tive voltage level on terminal 148.
During the off-time period 89 of the transmitter signal, no signal is present on conductor 202, and the voltage signal applied to the noni~verting input of -the operation amplifier 210 is essentially a-t the negative power supply voltage a-t ~ ~ @
~2 ~
terminal 148. The output terminal of the operational amplifier 210 is also held at the negative power supply voltage of terminal 148 due to the discharged condition of the capacitor 216. The feedback resistor 218 assures -that the output terminal of the operational amplifier 210 is maintained at the negative supply voltage by balanc.ing the offset voltages produced by the operational amplifier 210 and the resistor 208.
Upon the detection of a current loading signal lQ from the transmitter 10, the operational amplifier 210 delivers pulses of current to the diode 214 and creates a voltage level on conductor 220 which is somewhat positive with respect to the negative supply voltage 148. The resulting signal on conductor 220 creates effects in the level indicator 132 and the reset section 134 which allow the capacitor 216 to charge to a level representative of the maximum level of the current loading frequency signal with respect to the nega-tive supply voltage. Stated another way, the voltage on capacitor 216 will be allowed to increase to ~0 one half of -the maximum peak to peak voltage of the signal present at the noninverting input terminal of the operational amplifier 210. The resistor 212 allows the voltage level on the capacitor 216 to increase at a predetermined rate and causes the voltage on capacitor 216 to reach its maximum value only after a predetermined number of comple-te cycles of the current loading transmitter signals have been conducted through the operational amplifier 210.
The voltage level on conductor 220 is supplied to a level detector means 222 of the level indicator section 132.
The level detector 222 is a bar and dot graph integrated circuit marketed under the designa-tion LM3914N. The level detector 222 has connected thereto a plurality of ten light-emitting diodes, each of which is re:Eerenced 48. The diodes 48 are arranged in a predetermined order alony a predetermined scale. Depending upon the voltage level on the conductor 220, one of the diodes 48 wil] be eneryized. A higher voltage level on the conductor 220 will eneryize a liyht-emittiny diode toward one end of the predetermined scale, and a lower voltage level will energize the light-emitting diode toward the other end of the predetermined scale. Bv noting the position of the light-emitting diode 48 which is energized, the relative strength of the transmitter signal is indica-ted.
The user can determine which of the various electrical devices in close proximity to the probe 46 (FIG. 1) containing lS the transducer 122 is conducting the current loading signal created by the transmitter 10.
The reset section 134 operates in conjunction with the level detector 132 to periodically allow the capacitor 216 to charge to a predetermined maximum voltage, to hold the maximum voltage for a predetermined period of time, and to ~h~ea~ter discharge to a condition ready for reception of another current loading signal supplied by the transmitterO
The reset section 134 includes a transistor 224 which is rendered conductive when one of the light-emitting diodes 25 48 is energized by the level detector 222. When transistor 224 becomes conductive, it triggers transistor 226 into conduction. Normally, transistor 226 is not conductive and capacitor 228 has charged through resistors 230 and 232 to a voltage level present between the positive supply voltage 146 30 and the negative voltage 148. A terminal 234 of the capacitor
TRACING ELECTRI~AL CONDUC'TORS BY
HIGH-FREQUENCY LOADING AND IMPROVED SIGNAL DETECTION
Background This invention relates to new an~ improve~ appara-tus and methods for tracing electrical conductors of both alte~nating and direct current electrical power, and more specifically it pertains to identifying circuit breakers, fwses, switches and other current conducting or handling devices connected to a source of electrical power.
It is oftentimes necessary to trace and identify particular cixcuits and electrical devices in a power distribution network, such as circuit breakers or fuses. Identification has typically been accomplished by practicing one or two manual techniques. One technique is to selectively disrupt power by opening the circuit breakers one at a time. When power is no longer present at the circuit, electrical device or feeder conductor in question, the opened circuit breaker identifies the item in question. The disadvantage to this technique is that electrical power is temporarily disconnected Erom each of the circuits and branch conductors in the course oE the search, and it may be critical to maintain power to some o~ these circuits and branch conductors. Critical circuits include those which supply power to hospital equipment, computers, and many other types of sensitive electronic equipment. Another disadvantage is that a considerable amount of time is consumed in selectively and individually opening each of the circuit breakers. The second manual technique of identifying a circuit breaker is to introduce a sufficiently high electrical current load on the particular branch conductor to trip the circuit breaker or open the ~,..
,~
9~
fuse. This technique is typically achieved by introducing an intentional short circuit to the branch conduc-tor. l'he disadvantage of this technique is -that the power will then be totally disrupted, crea-ting the detrimental consequences previously mentioned. The increased curren-t drawn by the short circuit can create dangerous ~omentary overheatiny or fire conditions or can cause larger trunk or distribution breakers to trip open at the same time the branch circuit breaker is tripped open. Of course, once a distribution breaker trips open, a large number of branch and distribution conductors will be disconnected from the source of electrical power.
A variety of test instruments are also available for testing and determining a variety of different electrical conditions including tracing and identifying feeder conductors, circuit breakers and other current conducting devices as well as tracing and identifying short circuited conductors.
Certain of these prior art devices require interruption of power to -the conductors in order to accomplish the tracing 20 an~ identification. Other types of prior art devices employ means which cyclically create a current load on a particular conductor of sufficient magnitude to allow the increased current load, and hence the electrical device, to be identified wi-th a conventional ammeter or impedence measuring device.
Still other types of prior art devices introduce a relatively high-frequency signal on the conductor while conventional power is maintained and high-frequency signal is inductively detected. The high-frequency signal detection apparatus offers the best potential for reliable and simple circuit identification and detection, but such prior art devices are ~z~9~
typically subject to adverse and detrimental influences, such as false signals resulting from spurious signals Eron transients and switching currents, reduced sensitivi-ty for detecting and identifying the desired feeder condùc-tors through panel enclosures and tubular conduits, and a somewhat limited specificity in isolatiny one particular corlductor from a number of other conductors loca-ted in close proximity.
Other disadvantages of such prior art systems and methods are known to those appreciating this particular field and its problems, and will be made more particularly apparent with comprehension of -the desirable features of the presen-t invention.
.3_ 12~
Summary It is the general objective of this invention to provide a new and improved apparatus and method :Eor tracing and identifying electrical conduc-to:rs whlch eY~h:ib:it-, a relatively high imrnuni-ty to adver~e influences frvm spllr:ious signals such as transients and switching currents, which does no-t require the interrup-tion of applied power duri.ng the testing and tracing procedures, which exhibits a relatively high sensitivity and selec-tivity for more precisely identifying the particular electrical circuit conductor out of a closely assembled group without disassembly of various housings and enclosures containing the feeder conductor, and which is rendered substantially insensitive to different magni-tudes of voltage applied over the power distribution network.
In accordance with the present invention, there is provided an apparatus for tracing and identifying an electrical current carrying conduc-tor or similar means which is energized and is carrying current therethrough at a power frequency. The apparatus comprises, in combination, transmitter means and receiver means. The -transmitter means is adapted for connection tO -the conductor for drawing electrical current from the energized conductor in repetitious transmission duty cycles, each transmission duty cycle being a predetermined waveform having a -first predetermined time period during which a plurallty of current pulses are drawn from the energized conductor at a predetermined frequency and a seconcl predetermined time period during which no current is drawn .Erom -the conduc-tor.
The current pulses drawn during the first predetermined time period are suEficient to induce about the conductor a predetermined electromagnetic field having a frequency charac-teristic corresponding to the prefletermined :Erequency of the current pulses drawn duxing the first predetermined -time period. The predetermined Erequency is so substantially different from -the power freqwency a-t which current is otherwise conducted that the detection o~ the predetermined electromagnetic Eield a-t a predetermined ~requency i~
substantially independerlt of the magnitude oE the current otherwlse conducted by the energi~ed conductor relati~e -to the magnitude of -the current pulses drawn by the transmi-tter means. The receiver means is operative when positioned in relation to the conductor for detecting the frequency characteristic and determining the strength of the predetermined electromagnetic field induced by the curren-t pulses during the first predetermined -time period by the transmitter means. The receiver means also includes means for indicating the relative strength of the predetermined electromagnetic field at the predetermined frequency.
The inven-tlon itself is more precisely defined by the appended claims. The improvements and concepts from the presen-t invention are more specifically de~cribed in the accompanying description of the preEerred embodiments takerl in conjunction with the drawings.
Drawings FIG. 1 is a generalized and schema-tic view of a transmitter and a receiver o~ the present in~ention illustra-ted in conjunction with a schematic electrical power distrib~-tion networ'~.
FIG. 2 is a schematic diagram of one em~odimen-t of the transmitter shown in E'IG. 1.
FIGS. 3A, 3B, 3C, 3D, 3E, 3F, 3G, 3H and 3I are waveform diagrams illustrating the operation of the transmitter shown in FIG. 20 FIG. 4 is a schematic view of one embodiment of the receiver shown in FIG. 1.
FIG. 5 is a waveform diagram utilizing the same time reference as employed in FIGS. 3A to 3I, illustrating the operation of the receiver shown in FIG. 4.
FIG. 6 is a schematic di.agram of an alternative portion of the receiver shown in FIG. 4.
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Pre~erred Embodiments The two basic components of the presen-t inven-tion are a transmitter 10 and a receiver 12 shown in FIG. 1. The transmitter 10 is electrically connected in-to a power distribution network through which electrical power is supplied, as by connecting a plug prony 14 of the -transmi-t-ter 10 into a convenience outlet 16l for example. The convenience outlet 16 is electrically connected to a branch line or conductor 18 extending from a load center 20. Other branch lines, e.g. 22 and 24, also extend from the load center 20 and are connected with other elements such as additional convenience outlets 16a and 16b. Electrical power is supplied to the branch conductors 18, 22 and 24 through branch circuit breakers 26, 28 and 30, respectively, which are located within the load center 20. Neutral conductors 32 return current flow from the branch conductors 18, 22 and 24 to -the load center at a neutral bus 34. Electrical power is supplied to the load center 20 from a secondary line transformer 36, a plurality of feeder conductors 38, a plurality of main distribution breakers 40 and a plurality of distribution collductors 42 of the power distribution network, as is typical. A ground conductor 44 also extends through the power distribution network between the secondary line transformer 36 and each neutral bus 34. The branch circuit breakers 26, 28 and 30 protect the branch conductors 18, 22 and 24, respectively, from current overload conditions by trippin~ open upon the occurrence of an increased current drawn through any one of the branch lines. Similarly, the main distribution breakers 40 protect the distribution conductors 42 from current overload conditions.
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The transmitter 10 receives electrical power from one of the branch conductors, e.g. 18, and draws or absorbs current from that particular branch line in a prede-terMined pattern or waveEorm. The predetermined pat-tern or curren-t waveform drawn from the particular branch conduc-tor to which the transmitter is connec-ted induces a predetermined electromagnetic field directly rela-ted to the current waveform. The electromagnetic field extends along all of the branch conductors and each of the elec-trical devices operatively connected with these conduc-tors. For example, when the transmitter 10 is connec-ted into the branch conductor 18, the electromagnetic field is present at the branch conductor 18, the branch circuit breaker 26, and at one of -the distribution conductors 42 and main distribution circuit breakers 40 and feeder conduc-tors 38 electrically connected to the branch line circuit breaker 26 and over the neutral conductor 32.
The receiver 12 includes an electromagnetic field transducer means positioned at the distal end of a probe 46.
The receiver 12 operatively senses the strength of the predetermined electromagnetic field, rejects substantially all other signals and operatively indicates the strength of the electromagnetic field by lighting one of a plurality of indi.cators 48. In this manner, branch conductors, electrical devices connected to the branch conductors, branch circuit breakers, dis-tribution conductors, main distribution breakers, the feeder conductors and the neutral conduc-tors can be traced and identified without interrupting the supply of power from the power distribution network.
Idcntification proceeds by placing the transducer means of the probe 46 adjacent each of the electrical devices ~2~9~
in question and noting the field strength indication on the indicators 48 with respect to each. The par-ticular electrical device exhibiting the greatest field streny-th lndi.ca-tion is the device identified. As will become more apparen-t, the nature and operation o:E each transmit-ter 10 and receiver 12 provide an imp:roved capability for traciny and i~entifying electrical devices.
One embodiment 10' of the transmitter 10 is better understood by reference to FIGS. 2 and 3A to 3I. As shown in FIG. 2, the transmitter 10' comprises a power supply circuit 50, a duty cycle controller 52, a gated oscillator 54, a driver circuit 56, and an output circuit 58. The power supply circuit 50 generally draws applied AC or DC power from the power distribution network through the plug prongs 14.
Alternating current power is rectified by a full wave rectifier 60 and pulsating direct current power (FIG. 3G) is applied on conductor 62 to a conventional integrating and regulating circuit comprising a transistor 64, a Zener diode 66, a capacitor 68, and the resistors 70 and 72.
Regulated DC power is thereby present on terminal 74 and is conducted to other active components of the elements 52, 54, 56 and 58 of the transmitter 10'.
In the duty cycle controller 52, a pair of capacitors 76 and 78 are electrically connected in series between the terminal 74 and a ground reference 80. The input terminal to an inverting Schmitt trigger 82 is connected to the terminal 3A between capacitors 76 and 78. The output terminal 3B of the Schmitt trigger 82 is connected to the input terminal 3A through a parallel-branch feedback network comprising resistors 84 and 86 and a diode 88. The ~9~
capacitors 76 and 78, the resistors 84 and 86, and the diode 88, in conjunction with the Schmit-t trigger 82, form a resistive capacitive timing network of the du-ty cycle controller.
Capacitors 76 and 78 charye and discharge at terminal 3A in accordance with the waveform diagram shown in FIG. 3A. The output waveform from the Schmit-~ triyger 82 at terrQinal 3B
is illustrated in FIG. 3B. Accordingly, the two time periods established by the timing network, as shown in FIGS. 3A and 3B: a considerably longer off-time period 89, for example approximately 900 milliseconds, and a considerably shorter on-time period 91, for example approximately 45 milliseconds.
The ratio of the on-time period 91 to the off-time period 89 is controlled by the ratio of the sum of the resistances of resistors 8~ and 86 to the resistance of the resistor 84.
The on-time period 91 and the off-time period 89 are controlled by the values of the resistors 84 and 86 in relation to the values of capacitors 76 and 78. The diode 88 operatively connects the resistor 86 in the feedback path of Schmitt trigger 82 during the on-time period 91 but eliminates the ~o resistor 86 from -the feedback path during the off-time period 89.
The sated oscillator 54 is operative during the on-time period 91 when a diode 90 connected between terminal 3B and an input terminal 3C of an inverting Schmitt trigger 92 ~5 is not conductive. A capacitor 94 is connected between terminal 3C and the ground reference 80. A resistive feedback path defined by resistor 96 and potentiometer 98 is connected between an output terminal ~D of the Schmitt trigger 92 and its input terminal ~C. When the potential of the signal at terminal 3B attains its minimum level during the off-time period 89, the diode 90 is conductive. The voltage increases on capacitor 94 until the trip point of the Schmitt trigger 92 is attained. At the trip point, the resistive feedbac~ path of the resistor 96 and potentiometer 98 in conjunction with the capacitor 94 causes the Schmitt trigger 92 ~o oscillate at a frequency established by the valu~s of the elements 9~, 9~ and 98, for example about 6 kH~. The frequency of oscilla-tion can be adjusted by varying the resistance of the potentiometer 98.
The oscillation occurring durin~ the on-time period 91 is illustrated in FIGS. 3C and 3D, with FIG. 3C illustrating the input signal at terminal 3C and FIG. 3D illustrating the output signal at terminal 3D from the Schmitt trigger 92.
Four parallel-connected, inverting Schmitt triggers 100, 102, 104 and 106 primarily define the driver circuit 56.
15 The Schmitt triggers 100, 102, 104 and 106 receive as an input signal the signal at terminal 3D shown in FIG. 3D.
The Schmitt triggers of the driver circuit 56 provide added current to drive a transistor 108 of the output circuit 58.
The waveform at the common output terminal 3E of the Schmitt 20 triggers 100, 102, 104 and 106 is shown in FIG. 3E.
The output circuit 58 draws high freqency alternating current from the power distribution network when the transistor 108 is conductive. Of course, the transistor 108 conducts in accordance with the alternating high frequency current established during the on-time period 91 of the waveform, shown in FIG. 3E. When conductive, the transistor 108 operatively connects resistors 110 and 112 between the conductor 62 and the ground reference 80. Since the transistor 108 conducts in accordance with its input signal (FIG. 3E) during the on-time period 91, a high frequency current is conducted through resistors 110 and 112 as shown by the current waveform in FIG. 3H. FIG. 3G illustrates -the voltage waveform present on conductor 62 and at termina] 3G. A gas indicator bulb 114 lights during the time periods tha-t the transistor 108 is conductive and indica-tes -the opera-tion of the transmitter 10.
The high frequency rectified curren-t load:iny shown in FIG. 3H is conducted Erom the full wave rectifier 60 over conductors 115 and 116 to the pronged plug 14, as the alternating waveform shown in FIG. 3I. A varistor 118, is connected between conductors 115 and 116 to protect the transmitter 10 from overvoltage conditions due to voltage transients, lightning and inductive spikes and the like and from possible improper use. A fuse 120 is connected in the conductor 116 to protect the transmitter from excessive currents.
One of the significant advantages of conducting a high frequency current loading signal from the power distribution network in the duty cycle established by the on and off time periods 91 and 89 respectively, is that the high-frequency current-conducting transistor 108 does not experience ~0 excessive heating. The extent of heating of the transistor is related to the square of the voltage at the plug prong 14 during the time when the transmitter is conductive. In a practical embodiment, the transistor 108 can conduct as much as one amp of current which, during the time the transistor is conductive, results in significant heat creation. However, by operating with a duty cycle having a significantly long off-time period 89 as compared to the on-time period 91, the average effect of the heating is greatly reduced. The relatively large current conducted during the on-time period creates an electromagnetic field of sufficient strength ~9~
-to be reliably detected at significantly remote locations along the conductors within the power distribu-t~on network.
By not operating with a duty cycle characteristic, the strength of the field would be subs-tantially reduced, or relatively expensive and additional components would be - required to obtain comparable field s-tren~th~ A~cordinyly, the number and cost of the elements in the transmitter is reduced, the life of the transistor 108 is prolonged and -the reliability of the transmitter is enhanced.
One embodiment 12' of the receiver 12 is better understood by reference to FIG. 4. The receiver 12l includes a transducer means 122, a filter section 124, a variable gain section 126, an indicator section 128, a peak detector 130, a level indicator 132, and a reset section 134 operatively connected together. In addition, the receiver 12' includes a ground reference section 136 for maintaining the voltage reference levels of the elements of the receiver 12l.
The receiver 12' receives energy from self-contained batteries 140 and 142 of -the ground reference sec-tion 136.
The battery 140 is electrically connected be-tween terminals 146 and 148 to operatively establish a positive vol-tage level on teLminal 146 and a negative voltage level on terminal 148. The positive and negative voltage levels at terminals 146 and 148, respectively, are equally spaced above and below ~5 ground reference 144 and are maintained in the equally spaced relationship by the operational amplifier 150, the resistors 152 and 154 ancl the capacitor 156 connected in a known operative arrangement.
The transducer 122 is of the inductive type and utili~es an inductor or coil 160. A capacitor 162 is connected ~23 9~
in parallel relationship with the inductor 160, and the capacitor-inductor combina-tion is a -tuned or resonant clrcui-t with a resonant frequency equal to -t~e frequency o~ -the curren-t loading pulses delivered by the transmi-tter 10 during -the on-time period 91. A resistor 164 is connected between the coil 160 and capacitor 162 and the inver-ting input terminal of an operational amplifier 166. The reslstor 16~ reduces the effects of ringing in the tuned circuit 160 and 162 which may occur as a result of high-frequency transients that appear randomly and spuriously on the conductors of the power distribution network. A feedback loop defined by a capacitor 168 and resistor 170 is connected between the output terminal of the operational amplifier 166 and its input terminal. The values of elements 164, 168 and 170 establish the operational amplifier 166 as a lo~ gain, low pass frequency amplifier. Accordingly, the signal inductively received by the tuned circuit 160 and 162 is amplified to a magnitude well within the range between the positive and the nega-tive voltage supply levels established by the ground reference section 136. The values of the elements 16~, 166, 168 and 170 also operatively establish a roll-off frequency point, for example about 35 kHz, at a frequency substantially higher than the high-frequency signal from the transmitter 10 but substantially less than the major high-frequency components of voltage transients and spikes. A very flat gain response is thereby obtained between -the frequency of the transmitter signal and the power line frequency, typically 60 Hz. Consequently, the power line frequency will not be amplified more than the transmitter signal frequency, and the high frequency transients and spikes will be attenuated.
The filter section 124 basically comprises three serially connected filter means, 172, 174 and 176. Each of the filter means 172, 174 and 176 is an iden-tical Sallen-Key band-pass filter of well-known circuit configura-tion. The component values of each Sallen-Key band-pass Eil-ter are selected to provide a low Q for each individual filter, for example approximately two. As is well known, a Q is one measure of the ability of a band-pass filter to pass a particular range of frequencies. One definition of Q is the center frequency of the band pass filter divided by the frequency band width which the filter passes. Band-pass filters with high Q's are more susceptible to ringing than band-pass filters of lower Q's. During ringing a band-pass filter is rendered inoperative for its intended purpose. By placing three relatively low Q filters in series, the total Q of the filter section 124 for band-pass purposes is the sum of the Qs of each filter. For example, if each of the filters 172, 174 and 176 has an individual Q of two, the to-tal Q of the filter section 124 is approximately six with respect to filtering the desired signal. The ability of the filter section 124 to withstand the effects of ringing from high-frequency transients is not related to i-ts total Q, as it would be in the case of a single high Q filter. Instead, the ability to withstand ringing in the filter section 124 is related to the ability of one of the filters 172, 174 or 176 to withstand the potential for ringing. As an important result, the filter section 124 is highly selective in passing only the transmitter signal but is not highly susceptible to ringing. Accordingly, the signal present on conductor 178 is essentially a signal directed related -to the high-frequency 'I '~ "
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current loading created by the transmitter 10. The alternating power frequency has been selectively removed by the operational effects of the Sallen-Key fi].ter means 172, 174 and 176. In addition, the effects of high-frequencies have been siynifican-tly attenuated by the coil 160 and capaci.tor 162, and by -the resistive capacitive network of elemen-ts 164, 168 an~ 170.
The three Sallen-Key band pass filter means 172, 174 and 176 even further isolate and supply the signal created by the transmitter 10.
The signal available on conductor 178 is general].y referenced positively with respect to ground 144. The positive reference results because each of the operational amplifiers of the Sallen-Key band-pass filters 172, 174 and 176 are referenced directly to ground 144 without current offsets.
It is the general function of the variable gain section 126 to amplify the signal on conductor 178 and to reference that signal midway between the positive and negative voltage levels at terminals 146 and 148. The signal on conductor 178 is applied through a potentiometer 180 and a resistor 182 to the inverting input of an operational amplifier 184. A feedback network comprising resistors 186, 188 and 190 and a multiposition switch 192 is provided to adjust the gain of the operational amplifier 184. By positioning the switch 192 in one of its three positions, one or more of the resistors 186, 188 and 190 is connected in the feedback network to control the gain. The various stages of gain provided by the feedback network accommodate different strengths of signals detected. It is apparent that the high-frequency current drawn by the transmitter 10 induces a -17~
signal strength in the conductors which diminishes in accor-lance with the length over which the signal is conduc-ted, the number of elements through which the signal mus-t be conduc-ted and the presence of an exterior shieldiny enclosure. The highest gain available is when the switch 192 i~ open an~
all resistors 186, 188 and 190 are connected in -the fee~back loop~ The highest level of gain is desirable for identlfying current carrying devices i.n panel boxes or distribution or feeder conductors. In the medium gain setting, where resistors 186 and 190 are connected in the feedback loop, the gain is generally sufficient for tracing and identifying circuit breakers and switches. The low stage of gain, when switch 192 connects only resistor 186 in the feedback loop, is useful for detecting accessible branch conductors, for example.
With the appropriate level of gain established, the signal supplied from the output terminal of the operational amplifier 184 is supplied to an inverting input terminal of an operational amplifier 194 of the indica-tor section 128.
The current supplied from the operational amplifier 194 drives ~0 a piezoelectric speaker 196. The speaker 196 supplies an audio signal at the frequency of the current loading signal from the transmitter 10, for example 6 kHz. This frequency of the transmitter signal is easily audibly perceived by the user as an assurance of proper identification and use of the transmitter 10 and receiver 12.
Feedback from the output terminal of the operational amplifier 194 is conducted from the audio indicator section 128 through a resistor 198 to the noninverting input of the operational amplifier 184 of the variable gain section 126.
A capacitor 200 charges to the center level of the signal ~9~
clelivered from the operation amplifier 194. Since the operational amplifiers 184 and 194 each invert their inpu-t signals, the signal presen-t on capaci-tor 200 i.s essentially of the same polarity as the average center level of -the signal supplied to the inver-ting input term.inal of the operational amplifier 184. AccordincJly, the signal supplied at the output terminal of the opera-tional amplifier 184 is centered with respect to the ground reference 144 and this signal is applied on conductor 202 to the peak detector section 130.
In the peak detector 130, the signal on conductor 202 passes through capacitor 204 which, in conjunction with resistor 206, changes the level of the signal on conductor 202 from being referenced to the ground reference 14~ to being referenced to the negative voltage level at terminal 148.
A resistor 208 is connected between the noninverting input of an operational amplifier 210 and the capacitor 204. The resistor 208 prevents current from being drawn from the capacitor 204 when the voltage on the capacitor 204 swings ~0 below the negative voltage level at terminal 148 on every other half cycle of the signal on conductor 202. Output current delivered from the output terminal of the operational amplifier 210 is conducted through a resistor 212, a diode 214 to a capacitor 216. As will become more apparent, the capacitor 216 is normally maintained in a discharged condition with respect to the nega-tive voltage level on terminal 148.
During the off-time period 89 of the transmitter signal, no signal is present on conductor 202, and the voltage signal applied to the noni~verting input of -the operation amplifier 210 is essentially a-t the negative power supply voltage a-t ~ ~ @
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terminal 148. The output terminal of the operational amplifier 210 is also held at the negative power supply voltage of terminal 148 due to the discharged condition of the capacitor 216. The feedback resistor 218 assures -that the output terminal of the operational amplifier 210 is maintained at the negative supply voltage by balanc.ing the offset voltages produced by the operational amplifier 210 and the resistor 208.
Upon the detection of a current loading signal lQ from the transmitter 10, the operational amplifier 210 delivers pulses of current to the diode 214 and creates a voltage level on conductor 220 which is somewhat positive with respect to the negative supply voltage 148. The resulting signal on conductor 220 creates effects in the level indicator 132 and the reset section 134 which allow the capacitor 216 to charge to a level representative of the maximum level of the current loading frequency signal with respect to the nega-tive supply voltage. Stated another way, the voltage on capacitor 216 will be allowed to increase to ~0 one half of -the maximum peak to peak voltage of the signal present at the noninverting input terminal of the operational amplifier 210. The resistor 212 allows the voltage level on the capacitor 216 to increase at a predetermined rate and causes the voltage on capacitor 216 to reach its maximum value only after a predetermined number of comple-te cycles of the current loading transmitter signals have been conducted through the operational amplifier 210.
The voltage level on conductor 220 is supplied to a level detector means 222 of the level indicator section 132.
The level detector 222 is a bar and dot graph integrated circuit marketed under the designa-tion LM3914N. The level detector 222 has connected thereto a plurality of ten light-emitting diodes, each of which is re:Eerenced 48. The diodes 48 are arranged in a predetermined order alony a predetermined scale. Depending upon the voltage level on the conductor 220, one of the diodes 48 wil] be eneryized. A higher voltage level on the conductor 220 will eneryize a liyht-emittiny diode toward one end of the predetermined scale, and a lower voltage level will energize the light-emitting diode toward the other end of the predetermined scale. Bv noting the position of the light-emitting diode 48 which is energized, the relative strength of the transmitter signal is indica-ted.
The user can determine which of the various electrical devices in close proximity to the probe 46 (FIG. 1) containing lS the transducer 122 is conducting the current loading signal created by the transmitter 10.
The reset section 134 operates in conjunction with the level detector 132 to periodically allow the capacitor 216 to charge to a predetermined maximum voltage, to hold the maximum voltage for a predetermined period of time, and to ~h~ea~ter discharge to a condition ready for reception of another current loading signal supplied by the transmitterO
The reset section 134 includes a transistor 224 which is rendered conductive when one of the light-emitting diodes 25 48 is energized by the level detector 222. When transistor 224 becomes conductive, it triggers transistor 226 into conduction. Normally, transistor 226 is not conductive and capacitor 228 has charged through resistors 230 and 232 to a voltage level present between the positive supply voltage 146 30 and the negative voltage 148. A terminal 234 of the capacitor
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228 -thereby achieves a voltage approximating the ne~ative supply voltage at terminal 148. The terminal 234 is connected to the gate termlnal of a field effect transistor 236. The source terminal of the transistor 236 is also connected -to -the negative supply voltage 148. When the gate terminal voltage and the source terminal voltage are approximately eq~lal, the transistor 236 becornes conductive to discharge the capacitor 216 through register 238. The transistor 236 remains conductive only during the time period that a signal is not present on conductor 220, i.e., when transistors 224 and 226 are not conductive. However, when transistor 224 becomes conductive under the condition of a signal being applied to conductor 220 and of one of the ligh-t-emitting diodes 48 becomes conductive, the terminal 240 of capacitor 228 is operatively connected to the nega-tive supply voltage at terminal 148. The voltage a-t terminal 234 immediately goes to a level substantially below the negative supply voltage at terminal 148 which causes the transistor 236 to become nonconductive. The capacitor 216 commences charging and continues to charge so long as the voltage at terminal 234 remains below the voltage at the negative supply voltage at terminal 148. This condition exis-ts for a sampling time period 239, shown in FIG. 5, the length of which is determined by the discharge period established by the values of the resis-tor 232 and capacitor 228. The time period 239 is substantially greater than the on-time period 91 of the transmitter signal but less -than the off-time period 89 of the transmitter signal (FIG. 3E). Accordingly, the capacitor 216 is in condition to charge to its maximum level during the time period 89 that the transmitter 10 creates lZ~
the current loading signal. For false spurious signals of short duration and of frequency comparable -to -the transmitter frequency, resistor 212 is conductive only momentarily and capacitor 216 does not attain a significant level -to operatively result in a discernably intelliyible indication at the light-emitting diodes 48 before the false siynal ~issipates.
The maximum vol-tage ]evel to which capacitor 216 is charged is maintained during the sampling time period 239. The maximum charge level is maintained on conductor 220 for a sufficient period of time 239 to allow the level detector 222 to energize the appropriate light-emitting diode 48 and indicate the maximum attained transmitter signal strength. By holding the voltage level on conductor 220 for the sample time period 239, a constant indication is available from one of the diodes 48 for an amount of time sufficient for intelligent observation. After the sampling time period 239 ends, the transistor 236 again becomes conductive and the capacitor 216 is immediately discharged through resistor 233. In the discharged condition during a reset tim~ period 241, the receiver awaits the reception of another current loading transmitter signal during the on-time period 89. Once the first cycle of the transmitter signal is conducted through the receiver 12' in the manner described, the capacitor 216 again starts charging to the maximum level during the sample period 239. After the appropriate light-emitting diode 48 has been energized to indicate the maximum attained transmitter signal strength, represented by the voltage level on conductor 220 and across capacitor 216, the capacitor 216 is again discharged during the reset time period 241. During -the reset time period 241, .~ I f"
the capacitor 228 recharges to the voltage level between the positive and negative supply terminals 146 and 148, respectively The length of the reset time period 24] is es-tablished by the values of the capacitor 228 and the resistors 230 and 232.
From the foregoing description, i-t is apparent that the receiver 12' operates during the sample tiMe period 239 to indica-te the presence and strength of the transmitter signal. The de-tected signal is effec-tively filtered by an improved filtering arrangement to eliminate or reduce the influence of spurious signals such as voltage transients.
Occasional spurious signals which may be coupled through the receiver to the diodes 48 remain only for a short period of time due to the lack of significant effects from false signals and/or the relatively short sample and reset periods of operation provided by the reset section 134. Any false or spurious signals are quickly eliminated from consideration because they do not continually cause the repeated energization of the same or approximately the same light-emitting diode, as would occur upon detection of a constantly applied transmitter signal of the same signal strength. Accordingly, not only does the receiver 12' utilize improved filtering techniques to eliminate many of the adverse effects of spurious signals, but its indication of the strength of the transmitter signal has the effect of substantially further eliminating various adverse effects. By causing the sample period 239 to be considerably longer than the on-time period 91 of the transmitter signal, a sufficient time frame is established whereby one group of current loading transmitter pulses will be detected and their signal strength established. By making the sample period 239 less than -the off-time period 89 of the transmitter -2~-signal, only one signal group from the transmit-ter will have an operative effect on the receiver 12. By makiny each period of receiver operation (the sum of periods 239 and 241) less than the period of the -transmi-tter du-ty cycle (the sum of periods 89 and 91), the receiver will be in con~i-ti.on to respond to each new signal supplied by the transm:itter~
Accordingly, the improved filtering and sampli.ny effec-ts of the receiver assure high -transmitter signal sensitivity and improved immunity to the effec-ts from spurious signals, to a degree which has heretofore been unavailable in the field of tracing and identifying electrical conducting devices.
Another embodiment of an improved receiver can be understood by reference to FIG. 6. The elements illustrated in FIG. 6 are an alternative to the Sallen-Key band-pass filter means 172, 174 and 176 employed in the filter section 124 of the receiver 12' shown in FIG. 4. The function of the elements shown in FIG. 6 is to provide more improved filtering than that available from the technique of serially connecting a plurality of relatively low Q band-pass filters. An even more improved and enhanced sensitivity and ability to reliably ~letect the transm.itter signal results.
The improved filter section 124' shown in FIG. 6 includes a prefilter means 242, a digital switching filter MeanS 243, and impedence converter means 244 and a terminal filter means 246. The prefilter 242 takes the form of a typical Sallen-Key band-pass filter which employs resistive and capacitive component values selected to primarily reduce the typical alternating current power frequency, i.e. 60 Hz, and other low frequencies to an acceptable level for preventing unnecessary influences on the digital switching fil-ter 243.
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The digital switching filter 243 has the capability of allowing only signals of a very narrow preselected main band-pass frequency to remain on conductor 248, as well as very low frequencies and harmonics of the main band-pass frequency. The other signals on conduc-tor 248 are in essence coupled to ground 144 and are no-t passed -to the impedence converter 244. Signals oE a spurious or random nature are therefore essentially coupled to ground since such signals typically do not fall within -the low fre~uency range or the precise narrow primary band-pass frequency range or harmonics of the primary band-pass frequency. In essence, the digital switching filter 243 will pass signals having a consistent repetitious phase angle relative to the phase angle of the signals of the primary band-pass frequency.
The digital switching filter 242 comprises a plurality of capacitors 25Q, 252, 254, 256, 258, 260, 262 and 264 which are connected between the conductor 248 and the eight output terminals of a one-of-eight input select switch 268. The switch 268 functions to connect one of its 20 output terminals to which the capacitors 250-264 are connected, to the ground reference 144. The one of the output terminals which is connected to ground is selected by a binary signal supplied on conductors 270. While the selected input is connected to ground reference 144, the remaining other inputs are disconnected from ground reference and are allowed to float, thereby not providing a conduction path through those other inputs to the ground reference. A binary counter 272 supplies signals on the conductors 270. A clock signal is supplied to the clock terminal of the binary 30 counter 272 from an oscillator 273, which comprises an -26~
~2~
inverting operational amplifier 274, a crystal 276, capacitors 278 and 280 and a resistor 282. The predetermined operational frequency of the oscilla-tor 273 is established and is very precisely regulated by the characteristics of the crystal 276. The oscillator frequency supplied to the clock input terminal of the binary counter 272 is an exact prede-termined multiple of the predetermined narrow band-pass frequenc~ of the digital switchlng filter 243, with the predetermined multiple being equal to the number of output terminals of the switch 268 to which capacitors are connected. For example, if the primary band-pass frequency of the digital switching filter is 6 kHz, the frequency of the clock pulses supplied by the oscillator 273 to the clock terminal of the binary counter 272 is 48 kHz.
For signals at the primary band-pass frequency of the digital switching filter 243, each of the capacitors 250-264 will charge or integrate over one eighth of each cycle of the signal. Each capacitor will eventually charge to a level equal to an average applied signal level during its conduction interval. Thereafter, when a current conduction path exists through each of the capacitors 250-264 during its conduction interval, the voltage level previously established on that capacitor is essentially equal to the voltage level present on conductor 248 during that time interval. The voltage level or signal on conductor 248 is thereby unaffected since the switchlng of -the capacitor 250-264 to ground reference 144 does not adversely shunt the signal level on conductor 248 to ground. However, for signals which are not in phase with the primary band-pass frequency or its harmonic multiples, each of the capacitors 250-264 will charge to ~21~
randomly different levels during the intervals when -they are connected individually to the ground reference 144. Accordingly, since there will be no similarity of the sigrlal levels on the capacitors 250-264 relative to -the applied signal on conductor 266 during the subsequent conductlon in-tervals, a substantial portion of the signal on conductor 248 will be shunted to ground 144 or will be smoothed by the effect of the capacitors 250 264 discharging to or from the conductor 248.
The end result is that all signals other than the primary band-pass frequency or its exact multiples are substantially attenuated on conductor 248.
The impedence converter 244 essentially buffers the impedence of the digital switching filter 243 with respect to the terminal filter 246. The impedence converter 244 also provides a desired amount of gain established by its feedback resistor 286. The signals which are allowed to pass from the digital switching filter 243 on the conductor 248 are passed through the impedence converter 244 on conductor 288 to the terminal ~ilter 246.
The terminal fil.ter 246 essentially comprises another typical Sallen-Key band-pass filter, the primary function of which is to attenuate any switching noise included with the signal on conductor 288. The terminal filter 246 also attenuates any harmonic frequency components that may be included with the signal. The terminal filter supplies its signal on conductor 178, to the other elements of the receiver 12' shown in FIG. 4. The receiver 12' otherwise functions in the manner previously described.
Due to the precise frequency passage characteristics of the digital switching filter 243, a highly reliable means ~2~
for filteriny or attenuating all spurious signals except the predetermined transmit-ter signal is achieved. Operation of the receiver 12 is thereby rendered even more immune to spurious signals, transien-ts and potent:ial rinying~ The receiver 12 becomes even more reliable in identifying an~
tracing electrical devices which concluct the predetermined transmitter signal.
The significant advantages and improvements available from the embodiments of the transmitter and receiver of the present invention have been described. The specificity of description has, however, been made by way of example. The invention itself is defined by the scope of the appended claims.
--2g--
228 -thereby achieves a voltage approximating the ne~ative supply voltage at terminal 148. The terminal 234 is connected to the gate termlnal of a field effect transistor 236. The source terminal of the transistor 236 is also connected -to -the negative supply voltage 148. When the gate terminal voltage and the source terminal voltage are approximately eq~lal, the transistor 236 becornes conductive to discharge the capacitor 216 through register 238. The transistor 236 remains conductive only during the time period that a signal is not present on conductor 220, i.e., when transistors 224 and 226 are not conductive. However, when transistor 224 becomes conductive under the condition of a signal being applied to conductor 220 and of one of the ligh-t-emitting diodes 48 becomes conductive, the terminal 240 of capacitor 228 is operatively connected to the nega-tive supply voltage at terminal 148. The voltage a-t terminal 234 immediately goes to a level substantially below the negative supply voltage at terminal 148 which causes the transistor 236 to become nonconductive. The capacitor 216 commences charging and continues to charge so long as the voltage at terminal 234 remains below the voltage at the negative supply voltage at terminal 148. This condition exis-ts for a sampling time period 239, shown in FIG. 5, the length of which is determined by the discharge period established by the values of the resis-tor 232 and capacitor 228. The time period 239 is substantially greater than the on-time period 91 of the transmitter signal but less -than the off-time period 89 of the transmitter signal (FIG. 3E). Accordingly, the capacitor 216 is in condition to charge to its maximum level during the time period 89 that the transmitter 10 creates lZ~
the current loading signal. For false spurious signals of short duration and of frequency comparable -to -the transmitter frequency, resistor 212 is conductive only momentarily and capacitor 216 does not attain a significant level -to operatively result in a discernably intelliyible indication at the light-emitting diodes 48 before the false siynal ~issipates.
The maximum vol-tage ]evel to which capacitor 216 is charged is maintained during the sampling time period 239. The maximum charge level is maintained on conductor 220 for a sufficient period of time 239 to allow the level detector 222 to energize the appropriate light-emitting diode 48 and indicate the maximum attained transmitter signal strength. By holding the voltage level on conductor 220 for the sample time period 239, a constant indication is available from one of the diodes 48 for an amount of time sufficient for intelligent observation. After the sampling time period 239 ends, the transistor 236 again becomes conductive and the capacitor 216 is immediately discharged through resistor 233. In the discharged condition during a reset tim~ period 241, the receiver awaits the reception of another current loading transmitter signal during the on-time period 89. Once the first cycle of the transmitter signal is conducted through the receiver 12' in the manner described, the capacitor 216 again starts charging to the maximum level during the sample period 239. After the appropriate light-emitting diode 48 has been energized to indicate the maximum attained transmitter signal strength, represented by the voltage level on conductor 220 and across capacitor 216, the capacitor 216 is again discharged during the reset time period 241. During -the reset time period 241, .~ I f"
the capacitor 228 recharges to the voltage level between the positive and negative supply terminals 146 and 148, respectively The length of the reset time period 24] is es-tablished by the values of the capacitor 228 and the resistors 230 and 232.
From the foregoing description, i-t is apparent that the receiver 12' operates during the sample tiMe period 239 to indica-te the presence and strength of the transmitter signal. The de-tected signal is effec-tively filtered by an improved filtering arrangement to eliminate or reduce the influence of spurious signals such as voltage transients.
Occasional spurious signals which may be coupled through the receiver to the diodes 48 remain only for a short period of time due to the lack of significant effects from false signals and/or the relatively short sample and reset periods of operation provided by the reset section 134. Any false or spurious signals are quickly eliminated from consideration because they do not continually cause the repeated energization of the same or approximately the same light-emitting diode, as would occur upon detection of a constantly applied transmitter signal of the same signal strength. Accordingly, not only does the receiver 12' utilize improved filtering techniques to eliminate many of the adverse effects of spurious signals, but its indication of the strength of the transmitter signal has the effect of substantially further eliminating various adverse effects. By causing the sample period 239 to be considerably longer than the on-time period 91 of the transmitter signal, a sufficient time frame is established whereby one group of current loading transmitter pulses will be detected and their signal strength established. By making the sample period 239 less than -the off-time period 89 of the transmitter -2~-signal, only one signal group from the transmit-ter will have an operative effect on the receiver 12. By makiny each period of receiver operation (the sum of periods 239 and 241) less than the period of the -transmi-tter du-ty cycle (the sum of periods 89 and 91), the receiver will be in con~i-ti.on to respond to each new signal supplied by the transm:itter~
Accordingly, the improved filtering and sampli.ny effec-ts of the receiver assure high -transmitter signal sensitivity and improved immunity to the effec-ts from spurious signals, to a degree which has heretofore been unavailable in the field of tracing and identifying electrical conducting devices.
Another embodiment of an improved receiver can be understood by reference to FIG. 6. The elements illustrated in FIG. 6 are an alternative to the Sallen-Key band-pass filter means 172, 174 and 176 employed in the filter section 124 of the receiver 12' shown in FIG. 4. The function of the elements shown in FIG. 6 is to provide more improved filtering than that available from the technique of serially connecting a plurality of relatively low Q band-pass filters. An even more improved and enhanced sensitivity and ability to reliably ~letect the transm.itter signal results.
The improved filter section 124' shown in FIG. 6 includes a prefilter means 242, a digital switching filter MeanS 243, and impedence converter means 244 and a terminal filter means 246. The prefilter 242 takes the form of a typical Sallen-Key band-pass filter which employs resistive and capacitive component values selected to primarily reduce the typical alternating current power frequency, i.e. 60 Hz, and other low frequencies to an acceptable level for preventing unnecessary influences on the digital switching fil-ter 243.
:~2~
The digital switching filter 243 has the capability of allowing only signals of a very narrow preselected main band-pass frequency to remain on conductor 248, as well as very low frequencies and harmonics of the main band-pass frequency. The other signals on conduc-tor 248 are in essence coupled to ground 144 and are no-t passed -to the impedence converter 244. Signals oE a spurious or random nature are therefore essentially coupled to ground since such signals typically do not fall within -the low fre~uency range or the precise narrow primary band-pass frequency range or harmonics of the primary band-pass frequency. In essence, the digital switching filter 243 will pass signals having a consistent repetitious phase angle relative to the phase angle of the signals of the primary band-pass frequency.
The digital switching filter 242 comprises a plurality of capacitors 25Q, 252, 254, 256, 258, 260, 262 and 264 which are connected between the conductor 248 and the eight output terminals of a one-of-eight input select switch 268. The switch 268 functions to connect one of its 20 output terminals to which the capacitors 250-264 are connected, to the ground reference 144. The one of the output terminals which is connected to ground is selected by a binary signal supplied on conductors 270. While the selected input is connected to ground reference 144, the remaining other inputs are disconnected from ground reference and are allowed to float, thereby not providing a conduction path through those other inputs to the ground reference. A binary counter 272 supplies signals on the conductors 270. A clock signal is supplied to the clock terminal of the binary 30 counter 272 from an oscillator 273, which comprises an -26~
~2~
inverting operational amplifier 274, a crystal 276, capacitors 278 and 280 and a resistor 282. The predetermined operational frequency of the oscilla-tor 273 is established and is very precisely regulated by the characteristics of the crystal 276. The oscillator frequency supplied to the clock input terminal of the binary counter 272 is an exact prede-termined multiple of the predetermined narrow band-pass frequenc~ of the digital switchlng filter 243, with the predetermined multiple being equal to the number of output terminals of the switch 268 to which capacitors are connected. For example, if the primary band-pass frequency of the digital switching filter is 6 kHz, the frequency of the clock pulses supplied by the oscillator 273 to the clock terminal of the binary counter 272 is 48 kHz.
For signals at the primary band-pass frequency of the digital switching filter 243, each of the capacitors 250-264 will charge or integrate over one eighth of each cycle of the signal. Each capacitor will eventually charge to a level equal to an average applied signal level during its conduction interval. Thereafter, when a current conduction path exists through each of the capacitors 250-264 during its conduction interval, the voltage level previously established on that capacitor is essentially equal to the voltage level present on conductor 248 during that time interval. The voltage level or signal on conductor 248 is thereby unaffected since the switchlng of -the capacitor 250-264 to ground reference 144 does not adversely shunt the signal level on conductor 248 to ground. However, for signals which are not in phase with the primary band-pass frequency or its harmonic multiples, each of the capacitors 250-264 will charge to ~21~
randomly different levels during the intervals when -they are connected individually to the ground reference 144. Accordingly, since there will be no similarity of the sigrlal levels on the capacitors 250-264 relative to -the applied signal on conductor 266 during the subsequent conductlon in-tervals, a substantial portion of the signal on conductor 248 will be shunted to ground 144 or will be smoothed by the effect of the capacitors 250 264 discharging to or from the conductor 248.
The end result is that all signals other than the primary band-pass frequency or its exact multiples are substantially attenuated on conductor 248.
The impedence converter 244 essentially buffers the impedence of the digital switching filter 243 with respect to the terminal filter 246. The impedence converter 244 also provides a desired amount of gain established by its feedback resistor 286. The signals which are allowed to pass from the digital switching filter 243 on the conductor 248 are passed through the impedence converter 244 on conductor 288 to the terminal ~ilter 246.
The terminal fil.ter 246 essentially comprises another typical Sallen-Key band-pass filter, the primary function of which is to attenuate any switching noise included with the signal on conductor 288. The terminal filter 246 also attenuates any harmonic frequency components that may be included with the signal. The terminal filter supplies its signal on conductor 178, to the other elements of the receiver 12' shown in FIG. 4. The receiver 12' otherwise functions in the manner previously described.
Due to the precise frequency passage characteristics of the digital switching filter 243, a highly reliable means ~2~
for filteriny or attenuating all spurious signals except the predetermined transmit-ter signal is achieved. Operation of the receiver 12 is thereby rendered even more immune to spurious signals, transien-ts and potent:ial rinying~ The receiver 12 becomes even more reliable in identifying an~
tracing electrical devices which concluct the predetermined transmitter signal.
The significant advantages and improvements available from the embodiments of the transmitter and receiver of the present invention have been described. The specificity of description has, however, been made by way of example. The invention itself is defined by the scope of the appended claims.
--2g--
Claims (19)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Apparatus for tracing and identifying an electrical current carrying conductor or similar means which is energized and is carrying current therethrough at a power frequency comprising in combination:
transmitter means for connection to said conductor and for drawing electrical current from said energized conductor in repetitious transmission duty cycles, each transmission duty cycle being a predetermined waveform having a first predetermined time period during which a plurality of current pulses are drawn from the energized conductor at a predetermined frequency and a second predetermined time period during which no current is drawn from the conductor, the current pulses drawn during the first predetermined time period being sufficient to induce about said conductor a predetermined electromagnetic field, the predetermined electromagnetic field created by the current pulses having a frequency characteristic corresponding to the predetermined frequency of the current pulses drawn during the first predetermined time period, the predetermined frequency being so substantially different from the power frequency at which current is otherwise conducted that the detection of the predetermined electromagnetic field at a predetermined frequency is substantially independent of the magnitude of the current otherwise conducted by the energized conductor relative to the magnitude of the current pulses drawn by said transmitter means; and receiver means operative when positioned in relation to said conductor for detecting the frequency characteristic and determining the strength of the predetermined electromagnetic field induced by the current pulses during the first predetermined time period by said transmitter means, said receiver means also including means for indicating the relative strength of the predetermined electromagnetic field at the predetermined frequency.
transmitter means for connection to said conductor and for drawing electrical current from said energized conductor in repetitious transmission duty cycles, each transmission duty cycle being a predetermined waveform having a first predetermined time period during which a plurality of current pulses are drawn from the energized conductor at a predetermined frequency and a second predetermined time period during which no current is drawn from the conductor, the current pulses drawn during the first predetermined time period being sufficient to induce about said conductor a predetermined electromagnetic field, the predetermined electromagnetic field created by the current pulses having a frequency characteristic corresponding to the predetermined frequency of the current pulses drawn during the first predetermined time period, the predetermined frequency being so substantially different from the power frequency at which current is otherwise conducted that the detection of the predetermined electromagnetic field at a predetermined frequency is substantially independent of the magnitude of the current otherwise conducted by the energized conductor relative to the magnitude of the current pulses drawn by said transmitter means; and receiver means operative when positioned in relation to said conductor for detecting the frequency characteristic and determining the strength of the predetermined electromagnetic field induced by the current pulses during the first predetermined time period by said transmitter means, said receiver means also including means for indicating the relative strength of the predetermined electromagnetic field at the predetermined frequency.
2. Apparatus as recited in claim 1 wherein the power frequency at which current is otherwise typically conducted by the conductor is approximately 60 Hz, and the predetermined frequency of current pulses drawn by said transmitter means is approximately 6,000 Hz.
3. Apparatus as recited in claim 1 wherein the predetermined frequency at which said transmitter means draws current pulses from said conductor is approximately at least in the order of magnitude of 100 times greater than the frequency of current otherwise normally conducted by said conductor means.
4. Apparatus for tracing and identifying an electrical current carrying conductor or similar means, comprising in conjunction:
transmitter means for connection to said conductor and for conducting electrical current through said conductor in repetitious transmission cycles, each transmission cycle being a predetermined waveform having a first predetermined time period during which a plurality of pulses of current are conducted at a predetermined frequency and a second predetermined time period during which no current is conducted, the first predetermined time period being less than the second predetermined time period, and the current pulses conducted during the first predetermined time period being of sufficient magnitude to induce about said conductor a predetermined electromagnetic field having a frequency characteristic corresponding to the predetermined frequency of current pulses conducted during the first predetermined time period; and receiver means responsive to the electromagnetic field about said conductor when placed in proximity of said conductor, said receiver means including (a) transducer means responsive to the electromagnetic field for supplying signals corresponding to the frequency and strength of the electromagnetic field of said conductor at the approximate location of said receiver means with respect to said conductor, (b) filter means responsive to signals from the transducer means and operative for passing detected signals having a predetermined frequency related to the predetermined frequency of the current pulses conducted by said transmitter means during the first predetermined time period and also operative for substantially blocking signals from said transducer means at other frequencies, (c) magnitude detector means responsive to the detected signals from the filter means and operative for deriving a magnitude signal representative of the strength or magnitude of the detected signal, (d) reset means operatively connected to said magnitude detector means and operative for supplying a signal related to the magnitude signal from said magnitude detector means during a sample time period and operative for concluding the signal related to the magnitude signal during a reset time period, the sample and reset time periods forming a portion of a detection cycle over which said reset means operates, (e) indicator means for indicating the relative magnitude of the signal related to the magnitude signal during each sample time period and for terminating the indication during each reset time period.
transmitter means for connection to said conductor and for conducting electrical current through said conductor in repetitious transmission cycles, each transmission cycle being a predetermined waveform having a first predetermined time period during which a plurality of pulses of current are conducted at a predetermined frequency and a second predetermined time period during which no current is conducted, the first predetermined time period being less than the second predetermined time period, and the current pulses conducted during the first predetermined time period being of sufficient magnitude to induce about said conductor a predetermined electromagnetic field having a frequency characteristic corresponding to the predetermined frequency of current pulses conducted during the first predetermined time period; and receiver means responsive to the electromagnetic field about said conductor when placed in proximity of said conductor, said receiver means including (a) transducer means responsive to the electromagnetic field for supplying signals corresponding to the frequency and strength of the electromagnetic field of said conductor at the approximate location of said receiver means with respect to said conductor, (b) filter means responsive to signals from the transducer means and operative for passing detected signals having a predetermined frequency related to the predetermined frequency of the current pulses conducted by said transmitter means during the first predetermined time period and also operative for substantially blocking signals from said transducer means at other frequencies, (c) magnitude detector means responsive to the detected signals from the filter means and operative for deriving a magnitude signal representative of the strength or magnitude of the detected signal, (d) reset means operatively connected to said magnitude detector means and operative for supplying a signal related to the magnitude signal from said magnitude detector means during a sample time period and operative for concluding the signal related to the magnitude signal during a reset time period, the sample and reset time periods forming a portion of a detection cycle over which said reset means operates, (e) indicator means for indicating the relative magnitude of the signal related to the magnitude signal during each sample time period and for terminating the indication during each reset time period.
5. Apparatus recited in claim 4 wherein the time duration of each detection cycle is different than the time duration of each transmission cycle.
6. Apparatus recited in claim 5 wherein each transmission cycle is defined by the first predetermined time period and the second predetermined time period, and each detection cycle is defined by the sample time period and the reset time period.
7. Apparatus recited in claim 5 wherein the sample time period is defined by a third predetermined time period and the reset time period is defined by a fourth predetermined time period, and the third predetermined time period is greater than the first predetermined time period and less than the second predetermined time period.
8. Apparatus recited in claim 7 wherein the first predetermined time period is less than one-half the sum of the first and second predetermined time periods.
9. Apparatus recited in claim 8 wherein the sum of the third and fourth predetermined time periods is less than the sum of the first and second predetermined time periods.
10. Apparatus recited in claim 4 wherein said indicator means further comprises:
a plurality of indicators; and level detector means having a plurality of output terminals and one input terminal, said level detector means further including means operatively connecting each of the output terminals to energize a corresponding one of said indicators, means operatively connected to the input terminal to apply the signal related to the magnitude signal from said reset means to the input terminal, said level detector means operatively energizing the indicators in a predetermined order in accordance with the magnitude of the signal related to the magnitude signal.
a plurality of indicators; and level detector means having a plurality of output terminals and one input terminal, said level detector means further including means operatively connecting each of the output terminals to energize a corresponding one of said indicators, means operatively connected to the input terminal to apply the signal related to the magnitude signal from said reset means to the input terminal, said level detector means operatively energizing the indicators in a predetermined order in accordance with the magnitude of the signal related to the magnitude signal.
11. Apparatus recited in claim 4 wherein:
said magnitude detector means further comprises a first capacitor and means for charging said first capacitor to a value related to the magnitude of the magnitude signal;
said reset means includes a first controllable switch means having two terminals electrically connected with said capacitor and also having a third terminal, said first switch means having electrical characteristics which control the extent of current conduction through the first and second terminals in accordance with a signal applied to its third terminal;
said reset means further includes a controllable timing circuit including a second capacitor, resistor means through which said second capacitor is charged and discharged in predetermined charge and discharge time periods, said controllable timing circuit further including a second controllable switch means electrically connected with said second capacitor in an operative relationship for charging and discharging said second capacitor; and said reset means further includes means electrically connected with said second capacitor to apply a signal to the third terminal of said first switch means for rendering the first switch means nonconductive during the sample period and for rendering the first switch means conductive during the reset period.
said magnitude detector means further comprises a first capacitor and means for charging said first capacitor to a value related to the magnitude of the magnitude signal;
said reset means includes a first controllable switch means having two terminals electrically connected with said capacitor and also having a third terminal, said first switch means having electrical characteristics which control the extent of current conduction through the first and second terminals in accordance with a signal applied to its third terminal;
said reset means further includes a controllable timing circuit including a second capacitor, resistor means through which said second capacitor is charged and discharged in predetermined charge and discharge time periods, said controllable timing circuit further including a second controllable switch means electrically connected with said second capacitor in an operative relationship for charging and discharging said second capacitor; and said reset means further includes means electrically connected with said second capacitor to apply a signal to the third terminal of said first switch means for rendering the first switch means nonconductive during the sample period and for rendering the first switch means conductive during the reset period.
12. Apparatus recited in claim 11 wherein said second controllable switch means is electrically connected with at least one of the output terminals of said level detector means and second controllable switch means is rendered electrically conductive for discharging said second capacitor upon energization of at least one indicator.
13. Apparatus recited in claim 4 wherein said filter means comprises a digital switching filter means, and said digital switching filter means comprises:
a plurality of phase capacitors;
selectable switch means having a plurality of output terminals and at least one switch select input terminal and at least one reference terminal, said selectable switch means operatively connecting a selected one of the output terminals to the reference terminal, the selected one of the output terminals being designated in accordance with signals at each switch select terminal;
oscillator means for supplying a periodic signal at a predetermined oscillator frequency, the predetermined oscillator frequency being essentially an even multiple of the predetermined frequency of current pulses delivered by the transmitter means during the first predetermined time period;
and counter means receptive of the signal from said oscillator means and for supplying to each switch select terminal signals representative of the count of the oscillator signal.
a plurality of phase capacitors;
selectable switch means having a plurality of output terminals and at least one switch select input terminal and at least one reference terminal, said selectable switch means operatively connecting a selected one of the output terminals to the reference terminal, the selected one of the output terminals being designated in accordance with signals at each switch select terminal;
oscillator means for supplying a periodic signal at a predetermined oscillator frequency, the predetermined oscillator frequency being essentially an even multiple of the predetermined frequency of current pulses delivered by the transmitter means during the first predetermined time period;
and counter means receptive of the signal from said oscillator means and for supplying to each switch select terminal signals representative of the count of the oscillator signal.
14. Apparatus recited in claim 4 wherein said transmitter means further comprises:
duty cycle control means for operatively establishing the first and second predetermined time periods and for supplying an energizing signal during the first predetermined time period;
gated oscillator means electrically connected to said duty cycle control means and receptive of the energizing signal for supplying a trigger signal oscillating at the predetermined frequency during the first predetermined time period;
load means for conducting current; and switch means receptive of the oscillating trigger signal and electrically connected to said load means and to said conductor for operatively conducting current pulses from said conductor to said load means at the predetermined frequency of the oscillating trigger signal.
duty cycle control means for operatively establishing the first and second predetermined time periods and for supplying an energizing signal during the first predetermined time period;
gated oscillator means electrically connected to said duty cycle control means and receptive of the energizing signal for supplying a trigger signal oscillating at the predetermined frequency during the first predetermined time period;
load means for conducting current; and switch means receptive of the oscillating trigger signal and electrically connected to said load means and to said conductor for operatively conducting current pulses from said conductor to said load means at the predetermined frequency of the oscillating trigger signal.
15. Apparatus recited in claim 4 wherein said filter means comprises a plurality of separate relatively low Q band-pass frequency filters electrically connected in series.
16. Apparatus recited in claim 4 wherein said filter means comprises a digital switching filter means.
17. Apparatus recited in claim 4 wherein said transmitter further comprises:
duty cycle control means comprising a binary coded decimal counter having a plurality of output terminals, and gate means electrically connected for receiving input signals from said output terminals of said binary coded decimal counter, said gate means supplying a signal having characteristics which define the first and second predetermined time periods in accordance with a predetermined relationship of each input signal applied to said gate means;
means for delivering clock pulses to said binary coded decimal counter; and current switching means electrically connected to said conductor and controlled by the signal from said gate means for conducting current from said conductor during said first predetermined time period.
duty cycle control means comprising a binary coded decimal counter having a plurality of output terminals, and gate means electrically connected for receiving input signals from said output terminals of said binary coded decimal counter, said gate means supplying a signal having characteristics which define the first and second predetermined time periods in accordance with a predetermined relationship of each input signal applied to said gate means;
means for delivering clock pulses to said binary coded decimal counter; and current switching means electrically connected to said conductor and controlled by the signal from said gate means for conducting current from said conductor during said first predetermined time period.
18. Apparatus as recited in claim 1 wherein the power frequency at which current is otherwise typically conducted by the conductor is in the order of tens of Hz, and the predetermined frequency of current pulses drawn by said transmitter means is in the order of thousands of Hz.
19. Apparatus as recited in claim 4 wherein said filter means comprises means responsive to a digital signal at a predetermined frequency and is operative for passing a predetermined frequency related to the predetermined frequency of the digital signal.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000449772A CA1219911A (en) | 1984-03-16 | 1984-03-16 | Tracing electrical conductors by high-frequency loading and improved signal detection |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000449772A CA1219911A (en) | 1984-03-16 | 1984-03-16 | Tracing electrical conductors by high-frequency loading and improved signal detection |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1219911A true CA1219911A (en) | 1987-03-31 |
Family
ID=4127421
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000449772A Expired CA1219911A (en) | 1984-03-16 | 1984-03-16 | Tracing electrical conductors by high-frequency loading and improved signal detection |
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| Country | Link |
|---|---|
| CA (1) | CA1219911A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108132405A (en) * | 2017-12-08 | 2018-06-08 | 广东电网有限责任公司江门供电局 | Identifier is charged in a kind of distribution low-voltage outlet |
-
1984
- 1984-03-16 CA CA000449772A patent/CA1219911A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108132405A (en) * | 2017-12-08 | 2018-06-08 | 广东电网有限责任公司江门供电局 | Identifier is charged in a kind of distribution low-voltage outlet |
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