US2749514A - Electronic testing instrument - Google Patents

Description

June 5, 1956 F. P. zAFFARANo ELECTRONIC TESTING INSTRUMENT 7 Sheets-Sheet l Filed Jan. 12. 1951 Bnventlor F. F Z affa mno ZU HS Gttorng June 5, 1956 F. P. ZAFFARANO ELECTRONIC TESTING INSTRUMENT 7 Sheets-Sheet 2 Filed Jan. l2, 1951 June 5, 1956 F. P. ZAFFARANO ELECTRONIC TESTING INSTRUMENT 7 Sheets-Sheet 5 Filed Jan. l2. 1951 June 5, 1956 A F. P. ZAFFARANO 2,749,514

ELECTRONIC TESTING INSTRUMENT Filed Jan. l2, 1951 '7 4Sheets-Sheet 4 Il 114|" lill-Fllll'l'lli .l

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H f5 Gttomeg OUTPUT TO NEXT COUNTER 9.2.4052@ QD ai( A ZON Z imo@ n: E538 magma #gli m MVL June 5, 1956 F. P. ZAFFARANO 2,749,514

ELECTRONIC TESTING INSTRUMENT Filed Jan. 12, 1951 7 Sheets-Sheet 5 F-ICL. =CONDUGTTNG TUBE =NONCONDUCTTNG TUBE DUAL-TRIODE TRXGGER CIRCUIT TAGES BINARY F|R5T SECOND THXRD FOURTH DECADE el?, STAGE STAGE STAGE `TTAGE Ciwy@ 0 @O @C @O @C o 1 C@ @O @C @O l Z @C C@ @C @O 3 O@ C@ @C @C 3 4 @C @O O@ @C TRANSTTORY T 5 C@ @OI @O OMITTED J\ Il C FEED BACK A 7 3@ o@ o@ @0 s EE NOTE T e @Q @0 M@ o@ TRANSTTORY e o@ @o @o 11 O@ C@ @O l Q I T Q OMITTED LG FEED`BACK B 1E Q C) O Q) O @9 6 C) Q) C) O C) @D T 14 (D C) C) C) 8 15 C) Q C) O S NOTE1- 5H1FT oF THTRD STAGE FROM C) T0 Q CAUSES FEED-BACK BUT H15 AME Bnvcntor 5H1FT A5 A RESULT oF FEE -BAEW'H DoEs NOT GAUGE ANY AGTToN 51NGE F P Zaffamm THE HWT 15 50 TRANSITORY THAT :sg

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ELECTRONIC TESTING INSTRUMENT Filed. Jan. l2, 1951 7 Sheets-Sheet 7 @16.5. TYPICAL INPUT CONNECTIONS INPUT SETTING INPUT CONNECTIONS TYPE OF TEST START +PDLSE PICICUP OF RELAY FUSE TOP START TINE NEASURED FRON INITIAL @RSM 1: *EE- ENERCIIZATION OF COIL TO CUI/L+ II- INSTANT FRONT CONTACT CUM. MAKE STOP CLD SES.

+PULSE DROP AWAY OF RELAY- -=I -PULSE START TINE MEASURED FROM INITIAL ggg@ DEENEROIZATION OF COIL TO COM+ INSTANT SACK CONTACT CUM. MAKE TOP CLUSES.

:O I-PULSE PICK-UP OF RELAY- {USE START TIME MEASURES FROM INITIAL T ENERCIZATION OF COIL To NELA Q: INSTANT SACK CONTACT CUMNAKE 5T0P OPENS.

+PULSE DROP AWAY OF RELAY '=I UKLESE START TINE NEASURED FROM INITIAL BREAK 2 DEENERSIZATION OF COIL TO CUM.+ I INSTANT FRONT CONTACT CUMNARE STOF' OPENS.

OSCILLATTNC CONTACT B' Y MEASURES TIME OCILLATINC MARE QP; I TART CONTACT IS CLOSED DURINS g55/in PERATED AT END OF A DEFINITE PERIOD oF CUMMAKE 5 TOPPERIOD OPERATlON.

OSCILLATINC CONTACT +PULSE f MEASURES TINE OSCILLATINC -PULSE 5 CI|||I START CONTACT IS CLOSED SUPPLYINC QQK POSITIVE ENERSY DURING COM+ -L -5TOP ADEFINITE PERIOD OF CUM. 'KE T: OPERATION.

MA o o +PUL6E SUPPLIES SINGLE OJSLIQ'EIYE -PULSE 1: 5mm MEASURES DURATION OF g'i A POSITIYE PULSE CUM.+ SUPPLIED AS BY A CONTACT CUMMAK TOP Summer ELECTRONIC TESTTNG INSTRUMENT Frank P. Zatarano, Rochester, N. Y., assigner to General Railway Signal Company, Rochester, N. Y.

Application January 12, 1951, Serial No. 205,656

3 Claims. (Cl. 324-68) This invention relates to testing instruments and more particularly pertains to an electronic device capable of accurately measuring time intervals.

The occasion frequently arises in the use or design of certain apparatus that a time interval need be accurately determined. Such a need arises, for example, when it is desired that the pick up or release time of a relay be known. One way of accomplishing this purpose is to provide an electronic device which is responsive to electrical signals identifying both the beginning and end of the interval to be timed so that it will count, during such interval, a series of regularly occurring pulses whose frequency is known. If the pulses to be counted during the interval are spaced at one millisecond intervals, for example, the number of such pulses counted during the interval demarcated by the identifying signals determines the length in milliseconds of such time interval.

Electronic counting circuits are particularly suitable in a device of this kind as they are capable of counting rapidly and accurately and are also readily controlled by the identifying signals which demarcate the beginning and end of the timed interval. In the test instrument of the present invention, the identifying signals may be any of several dilterent kinds. For example, the beginning of the interval may be represented by a positive or negative pulse or simply by the opening or closing of an external circuit; the end of the interval may independently be represented in a similar manner. Thus, by way of illustration, the timing action of the test device may be started by a negative pulse and ended by a positive pulse. As another possibility, the timing action may be started by the closing of a contact in some external circuit and ended by a negative Sttes arent pulse. Therefore, an object of the present invention is to Separate start and stop circuits are provided and each g may be selectively operated to respectively start and stop the timing operation. Occasionally it is necessary to measure the interval between the occurrence of a single event and the next-occurring one of a series of events which are independent of the single event. For example, it may be desired to find the time interval between the occurrence of a synchronizing pulse and the next-occurring one of a series of pulses. In that event the timing action of the timer can be started by the synchronizing pulse and ended by the next of the pulses in the series to occur after the synchronizing pulse. Thus, another object of this invention is to prevent the stop circuit from being eiective even though a proper signal is applied to the stop input of the timer unless the start circuit has first been operated.

To provide for resetting the timer to zero at the end of a timing operation, a reset switch is provided. An object of this invention is to prevent the start circuit from being operated by a start signal until the reset switch has rst been operated to hereby ensure that each interval may be independently recorded.

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Under certain circumstances it is required that a number of time intervals be cumulatively measured rather than independently. Another object of this invention, therefore, is to provide an organization in which each interval throughout which an identifying signal is applied to the timer is cumulatively timed. Yet another object is to permit starting or stopping of the cumulative measuring in response to a signal identifying either the beginning or the end, respectively, of the intervals to be recorded.

Another object is to provide an improved electronic counting organization wherein each step or stage of the counter is relatively unalected by undesirable feedback from the steps of the counter.

Other objects, purposes, and characteristic features of the present invention will be in part obvious from the accompanying drawings and in part pointed out as the description of the invention progresses.

Fig. l illustrates the control panel of the interval timer of the present invention;

Fig. 2 illustrates in block form the general organization of the present invention;

Figs. 3A and 3B, when placed side by side, provide a circuit diagram showing in detail the various circuits of the electronic interval timer;

Figs. 4 and 5 illustrate diagrammatically the manner of operation of the decade counter employed in the interval timer;

Fig. 6 diagrammatically shows the relationship between the scale readings and actual measured time intervals;

Fig. 7 illustrates the manner in which typical pick-up and drop away tests of a relay are made with the interval timer; and

Fig. 8 illustrates diagrammatically for various tests the connections between the device to be tested and the interval timer of this invention and the properpositions of the switches of the timer for the test being made.

To simplify the illustration and facilitate the explanation, the various parts and circuits constituting the embodiment of the invention are shown diagrammatically and certain conventional illustrations are employed. The drawings have been made to make it easy to understand the principles and manner of operation of this invention rather than to show the specific construction and arrange ment of parts that could be used in practice. The symbols and with their associated arrow tails and heads respectively designate the positive and negative terminals of a suitable supply voltage source having also a grounded tap connection. Y

General organization The block diagram of Fig. .2 illustrates the general or ganization of this electronic interval timer. The electrical signals which identify the beginning and end of the interval to be timed'are applied to the start and stop inputs respectively of the input switching circuits 1li. The input switching circuits include two multi-position switches 23 and 24 which adapt the circuit organization to the particular type of input selected to be applied to the start and `stop input terminals 2i and 22 respectively.

The pulse source 14 operates continually while the timer is energized and supplies an output of regularly occurring pulses to the counter gate i3. The condition of the counter gate determines whether the pulses from the pulse source 14 are applied to the units counter l5. When the counter gate i3 is open, the pulses are applied to the units counter and are counted by the units, tens, and hundreds counters 15, 16, and 17 respectively. When the counter gate 13 is closed, however, it blocks the pulses from the pulse source so that they cannot be applied to the counters. The start and stop signals from the input switching circuits control the start gate control l1 and stop gate control 12 respectively. Operation of the start gate control from its normal condition in response to a ..3 start signal causes the opening of the counter gate 13. Similarly, the operation of the stop gate control 12 from its normal condition in response to a stop input causes the ciosure of the counter gate 13.

"the pulses provided by the pulse source 14 are applied to the input of the units counter 15 when the counter gate 13 is open as has been described. Upon each tenth pulse appiied to it, the units counter 15 is restored to its original condition and a pulse is supplied to the tens counter 16 to operate the iirst step of this counter. When the tens counter is liually operated, the iirst step ot the hundreds counter 17 is operated. Thus, with three such counters as many as 999 counts may be recorded. Each counter such as the units counter 15 includes l() neon lamps which are selectively energized to give a visual indication or the measured time interval. The pulse source 14s preferably includes means for selecting between one of several pulse rates so that intervals of greatly varying length may be measured by this interval timer as will later be described in greater detail.

ln Fig. 2 the device to be tested is illustrated by way of example as a relay R whose pick-up time, i. e. the time from the application of energy to the winding until closure of the front contact, is to be determined. The opposite terminals of a suitable source of relay energy such as the battery 72 are connected to the energy terminals it? of the interval timer, and the relay winding is connected across the coil terminals 41. The contact 2u ot relay R is connected to one of the stop terminals and the associated front contact is connected to the other stop terminal. To test the relay pick up time, the pick tip-drop away switch 73 is operated to the pick up position. Operation of the reset-test switch 74 to the test position then completes a circuit including the battery 72 to energize the winding of relay R. The sudden voltage increase across the winding of relay R upon its energization causes a positive pulse to be applied to the start input terminals 21. When the relay R picks up, its front contact closes and shunts the stop terminals 22. The input switching circuits 1@ are properly conditioned, therefore, to measure the interval between relay energization and closure of the front contact when the start and stop slector switches 23 and 24 are placed in the +pu`lse and make positions respectively. The manner in which the connections are made and the various switches are positioned to malte this test and also other tests is diagrammatically illustrated in Fig, S.

Each time that the relay pick up time is to be measured, the 'reset-test switch 74 must be operated to 'the test position for a sulicient length of time to ensure the pick up of relay R. The regularly occurring pulses provided by the pulse source 14 are then applied through the counter gate 13, which is open between the time the relay 'is tirst energized until its front contact closes, to the decade counters 15, 16 and 17. With 'the number of pulses counted and their repetition rate known, the pick up time of the relay R is readily determined.

When the pick up time of relay R has been recorded upon the various counter units, the reset-test switch '74 is released. This switch is normally biased to the center position so that release of this switch opens the circuit to the winding of relay R and causes this relay to drop away. This switch must, therefore, Vbe again operated to the test position to cause the picking up of relay R. Before being operated to the test position for a subsequent measuring of the pick up time, the switch 74a is lrst operated momentarily to the reset position. This action causes the reset contacts 19 to restore the start gate control 11 and stop gate control 12 to their normal conditions. f, at the same time, the single-cumulative switch del is in the single position, the reset contacts 19 will cause the various decade counters 15, 16 and 17 to be restored to their normal conditions, thus effectively erasing the count stored in them. However, if this switch S4 is in the cumulative position, the reset contacts 19 cannot cause this erasure ot the count vstored in `the counters although the reset contacts 19 will still be effective to restore the start and stop gate controls 11 and 12 to their normal conditions.

When the time required for relay R to drop away and close its back contact 2t? following its deenergization is to be determined, the pick up-drop away switch 73 is operated to the drop away position. With the reset-test switch '-74 in either its neutral or reset positions, a circuit is completed including the battery 72 to energize the winding of relay R. if the switch 74 is momentarily operated to the reset position prior to the timing of the relay drop away time the relay R still remains energized. Howevery when the switch '7d is operated to the test position, the energizing circuit for relay R is opened so that this relay is dcenergized. The sudden decrease ot voltage across the winding of relay R causes a negative pulse to be applied to the start terminals Z1, so that the start selector switch Z3 should be operated to the Pulse position (see Fig. 8) to properly condition the input switching circuits 1t) for this starting signal. it the back contact 2t) instead of the yfront contact 2t? of relay R is then connected to the stop terminal, the stop terminals 22 will be shorted upon the closure of back Contact 26E. Thus, with the stop selector 'witch 24 in the maite position, the input switching circuits 1G are properly conditioned for this stop signal. As a result., the start and stop gate controls 11 and 12 will be effective to open the counter gate 13 only during the time linterval bett een the deenergization of the relay winding and the closure of bach contact 29 so that this interval wili be recorded upon the decade counters.

Under certain conditions, it is desirable that the interval timer cumulatively measure all the time intervals throughout which some particular condition is in existence. For example, it may be required to cumulatively measure all intervals during which some circuit contact is closed. For this reason the cumulative gate control 18 is provided which is effective as long as a selected input is applie'.. to the start or stop terminals to count cach time interval that such selected input is so applied. For example, it can be provided through the control ot the input switching circuits 10, that each interval during which a positive voltage exists at the start input be measured as indicated in Fig. 8 and that such time intervals be cumulatively recorded on the decade counters.

Detailed operation The pulse source la shown in Fig. 3A is continually Loperative when energy is applied to thc interval timer to supply output pulses of a particular selected rate. The pulse source may include a suitable oscillator having proper frequency stability characteristics and suitable pulse forming apparatus, and is so organized that its output consists of sharply peaked, negative-going pulses. A frequency selector switch is shown diagrammatically in block 14 of Fig. 3A, and operation ot this switch to its various positions is eiective to select among various pulse rates. Although various pulse rates may be employed in practice, Fig. 6 shows, by way of example, how the number of pulses actually counted in a timing operation may be interpreted, in view of the particular pulse frequency selected, to provide a reading in erms of some standard time unit of a .measured interval. In Fig. 6 the time unit in terms of which the various intervals are to be measured is chosen to be a millisecond. Thus, when the frequency selector switch associated with the pulse source 14 is operated to lthe scale reading 1, the output pulses of the pulse source occur at one millisecond intervals. Consequently, lthe number of pulses counted by the decade counter during some timed interval is multiplied by the factor 1 to obtain the length of time measured in terms of milliseconds. When the frequency selector switch is per'ated to the ten position, the repetition of the output pulses of the pulse source 14 is reduced by a factor of 10 as can be seen in Fig. 6 by comparing line A with line B. Using this scale, an observer must multiply the number of pulses counted in a time interval by a factor of l0 to obtain a measure of the timed interval in terms of milliseconds. Similarly, operation of the frequency selector switch to the 0.1 position causes an increase in the pulse rate by a factor of 1i) as is shown by a comparison of line C with line B. ln using this scale, an observer must multiply the number of pulses counted by one tenth in order to determine the length of a timed interval in terms of milliseconds.

The output pulses of the pulse source 14 are applied to the control grid of a tube included in the counter gate 13 (see Fig. 3A). The control grid of this tube is connected to ground through a grid leak resistor 26. No grid bias voltage is supplied for this tube 25 so that its grid is normally at the voltage of the cathode. The plate is connected to the source through a plate load resistor 27, and is also connected directly to the plate of tube 28 included in the cumulative gate control 18 so that resistor 27 is also the plate load resistor for this tube 2S. When tube 2S is nonconductive, it acts as a high impedance in parallel with tube 25 and so has but little effect upon the positive output pulses appearing at the plate of tube 25; but when tube 28 is conductive, it acts as a low impedance shunt for tube 25, thereby reducing the amplitude of the positive pulses at the plate of tube 25 to such an extent that they cannot operate the counters. As will presently be seen, however, tube 23 in the cumulative gate control 13 is normally nonconductive so that the positive pulses required to count time intervals are readily produced at the plate of tube 25.

The positive pulses at the plate of tube 25 are applied through a blocking condenser 29 to the plate of diode tube 39. The cathode of this diode is connected to (i-) through a resistor 31, and the plate is also connected through a resistor 32 and through a normally closed contact 33 of the reset-test switch '74 to As long as tube 35 and gas discharge tube 3% in the stop gate control 12 are nonconductive so that there is no plate current passing through resistor 32, the plate of diode is held at the same positive potential as the cathode. In this condition, the diode 30 is able to conduct in response to the positive pulses appearing at its plate so that corresponding positive pulses appear at its cathode and are applied through condenser 36 to the control grid of tube 37. If, however, tube or the gas discharge tube 39 is in a conductive condition, the flow of its plate current through plate load resistors 3S and 32 suciently reduces the voltage at the junction of these two plate load resistors so that the plate of diode 30 is substantially negative with respect to the voltage at its cathode. Under these circumstances, diode 30 cannot conduct in response to the positive pulses appearing at its plate so that positive pulses cannot appear at the input of tube 37. Thus, the stop control gas tube 39 and the electron discharge tube 35 must both be nonconductive to permit diode 3@ to pass po-sitive pulses to the input of tube 37. When either tube 35 or gas tube 39 is made conductive, diode Sii blocks the pulses from appearing at the input to tube 37.

Tube 37 is biased substantially to cut off bythe voltage dividing network including resistors 45 and 46 connected between the source of voltage and ground. These resistors together with condenser 36 comprise an R-C differentiating combination which produces sharp,posi tive pulses at the grid of tube 37. As tube 37 conducts in response to each positive pulse on its control grid, a co-rresponding negative pulse appears at its plate and is applied through a coupling condenser d'7 to the input of the units counter 15.

The start gate control 11 and the stop gate control 12 are together effective, as has been described, through the effects of tube 35 and gas discharge tube 39 to control' the application of pulses to the units counter 15. Whenever pulses are applied from the pulse source 14 and through the counter gate 13 to the units counter 15, they are registered upon the decade counters. In order that these pulses will not cause operation of the counter except during an interval to be timed, the normal condition of the apparatus is such that the counter gate 13 has its diode 3@ blocked. This result is accomplished by having gas discharge tube 50 included in the start gate control 11 in a normally nonconductive condition. The voltage supplied to the grid of tube 35 by the voltage dividing network including plate load resistor 4S and resistors 49 and 51 connected between (-i-) and is suiiciently high to make tube 35 conductive. Condenser 43 shunting resistor 49 is for the purpose of allowing the grid voltage of tube 35 to rapidly follow the voltage variations at the plate of tube 5t). Similar condensers are included in the grid circuits for tubes 2S and 81. Thus, tube 35 is normally conductive, and as explained, tube 35 is etective, when in a conductive condition, to block diode 30 so that positive pulses cannot be applied to the input o-f the units counter 15. lf, however, tube 50 is made conductive, its plate voltage is sufciently reduced to cut off tube 35 with the result that diode 30 is then no longer blocked. Thus, the electrical signal that identifies the beginning of the interval to be timed causes, as will be described, the conduction of gas discharge tube 5d with the result that the regularly occurring pulses from the pulse source 14 are applied to the units counter 15. This action continues until the end of the interval to be timed when the electrical signal identifying the end of the interval causes gas discharge tube 39 to become conductive, thereby again causing the diode 3d to block the pulses from the pulse source. Therefore, the circuit organization with respect to the start and stop gate control circuits and the counter gate 13 is such that both thyratrons 50 and 39 are normally nonconductive, gas tube 50 must be tired to start the timing action, following which gas tube 39 must be red to terminate the timing action.

The start selector switch 52 and the stop selector switch 53 are respectively arranged to select among the various kinds of input signals which may be applied to start and stop the intervals timing. When the timing action is to be started by a positive pulse, the start selector switch 52 is moved to the -lpulse position. The input signal is then applied to the start terminals 21 with such polarity that the upper terminal of resistor 76 is made positive with respect to its opposite grounded terminal. T he positive pulse is applied through contact 54 and condenser 55 to the control grid of tube 56. The start pulse may, if desired, be relatively broad because the time constant of condenser 55 and the associated resistive network in the grid circuit of tube 56 is sutliciently short to differentiate the leading edges of broad start pulses with the result that corresponding positive triggers appear at the control grid of tube 56. Tube 56 is preferably biased to cutoif by means of the voltage applied to its cathode through the voltage dividing organization including resistors 57 and 5S connected between and ground. Additional bias is provided by the voltage applied to the control grid through the voltage dividing network including resistors 59, et), and 6l. Switch 69 is included to permit varying the sensitivity of the start gate control to start pulses of various amplitudes. Thus, with the contact of switch 69 in its left-hand position, the junction of resistors 59 and 60 is connected to ground through contact $0 of the start selector switch 52. As a result, the grid is not biased by the voltage obtained from the source through resistor 60 and is biased instead only by the iixed cathode cutot bias. Consequently, a pulse of relatively low amplitude will cause tube 56 to conduct. When the junction of resistors 59 and 6) is connected to ground through potentiometer 61 and contact 54 by moving the Contact of switch 69 from its lefthand position, the grid of tube 56 assumes a more negative potential so that a larger amplitude pulse is required to make this tube conductive. By providing various positions of the switch 69 so that the junction of resistors 59 and et? may be connected through various resistance values to ground, various levels of sensitivity are obtainable. Such a control over the sensitivity of the start gate control il is desirable in that it provides for high sensitivity when only a low amplitude start pulse is available, but also permits a reduction in sensitivity when only part pulses above some mieuurn amplitude are to operate the start gate control.

The positive pulse at the control grid of tube 56 resulting from a positive start pulse produces a corresponding negative pulse at the plate of this tube which is then applied through an R-C differentiating combi tion including condenser 62 and resistor 63. Tube 64 is positively l ay having its control grid connected through resistor i533 to (l-). Therefore, cach negative pulse at the control grid of tube 6ft causes a decrease of plate current with a resulting increase of potential at the junction of plate load. resistors 65 and 66.

Gas discharge tube Si# is ordinarily biased to a nonconductive condition by the voltage dividing network including resistors d'7, et and 79. Condenser 71 shunting resistor 7u is for the purpose of reducing the ettect at the grid of tube :itl of transient voltage variations which might appear in the bias voltage supply. Each positive pulse applied to the control grid of tube Sil from tube est momentarily raises the grid voltage or tube i@ so that this tube becomes conductive. Although the pulse at the grid is of relatively short duration, tube ren-rains conductive when its grid-cathode voltage is increased above the cutoff: level since, in a gas discharge tube, grid control is lost when the tube becomes conductive. rhe operation ol` the start gate control 1l is such then that tube 56 is momentarily made conductive with the result that a positive pulse appears at the control grid of gas discharge tube Eil, thereby making tube Sti conductive. As has been described, this conductive condition of thyratron Sil iucreases the plate voltage of diode 3@ so that the pulses from the pulse source l@ may be applied through the counter gate i3 to the units counter l5.

When the start selector switch operated to the pulse position to condition the start gate control ll. for a negative start pulse, the start input signal appearing across the start terminals 2l and thus across re istor 7e is applied through Contact and condenser 75 to the cathode of tube S6. The time constant for condenser' 75 and the associated resistive network is suticiently short to provide negative triggers at the cathode of tube 56 even for relatively broad start input pulses. rlfhe increase ot' gridcathode voltage resulting from a negative start pulse causes tube Sri to conduct momentarily so that, :i manner similar to that just described, gas tube 513 is made conductive and diode 3u no longer blocks the pulses from the pulse source.

Operation of the start selector switch 5?; to the make position adapts the start input circuit for response to the closing of an external circuit connected across the start terminals 2l, thereby shouting the resistor 76 connected across the sta als. With the start selector switch 52 in the make position, connection is provided from and including contact 77, through contact 54 and resistor 76 to ground. As a result, the upper termii l ot resistor 7d is at some positive potential with respect to ground. When the start terminals El are shorted by the closing of an external contact, the voltage at the upper terminal of resistor .76 suddenly drops to ground potential and, since the voltage across condenser cannot instantly be changed, the voltage applied to the catsode of tube 56 suddenly is made more negative thereby increasing the grid-cathode voltage. Condenser 75 quickly discharges and a new steady-state condition is soon reached at which time the voltage at the cathode of tub 56 is restored to its normal value. Consequently, the effect or shorting resistor 76 through the external contact has the eltect of placing a negative pulse at the cathode of tube This pulse has the elect of causing tube to conduct with the result that gas tube 5% is made conductive. rhe diode 35i in the counter gate 13 is thus unblocked so that pulses from the pulse source 14. may be applied to the units counter 1S.

When the start selector switch 52 is moved to the break position, a connection is provided from and through resistor '78, contact 54, resistor 76, to ground. illith the start input selector switch in this position, the start gate control lil is conditioned to start the counting operation when an external contact normally shouting resistor 76 is opened. With the external contact normally shouting resistor 76, the lower terminal of resistor 78 is at ground potential. "vl/hen the external contact is opened, the voltage at the upper terminal of res or 7s is suddenly increased to some positive potential above ground, thereby producing a corresponding increase potential the grid of tube 56. Condenser quickly ornes changed so that the voltage at the grid ot tube o is restored to normal. The resulting positive at the grid ol the tube 56 makes this tube momentarily conductive so that gas tube Sil becomes conductive with the saine result as previously described.

The stop selector switch 53 controls the condition of the stop input circuits and the circuits are similar in most respects to the start input circuit just described. Thus, a similar organization is provided so that with the switch in the -l-pulse or Wpulse positions a positivegoing or negative-going pulse respectively will cause gas tube 39 to conduct, thereby resulting in the blocking of diode 3l). Also, the stop selector switch 53 in the make and break positions respectively, the closing or opening of an external circuit connected across the stop terminals 22 causes the gas tube 39 to tire. A switch contact '7l is included for the saine purpose the corresponding switch contact 69 associated with the start gate control ll. Thus, a sensitivity control is also obtained lor positive and negative stop pulses applied to the stop gate control 12.

The stop gate control differs from the start gate control in that the positive plate potential for gas tube 3@ is obtained from the plate ot tube 35 in the counter gate 13 rather than directly from the (l) voltage source as provided for gas tube Sil. Because of this connection, the plate voltage of gas tube 39 is so reduced when tube 35 in the counter gate is conductive that tube 39 cannot become conductive in response to a stop signal applied to the stop input terminals. Gnly when tube 35 is nonconductive is the plate potential of gas tube 39 sufficiently high to permit its being made conductive. The eiect then is that a stop signal is not ellective upon the stop gate control until the occurrence or' a proper start signal has caused gas tube Sil to conduct so that tube 3S becomes nonconducve.

Since the start selector switch S2 and thc stop selector switch S3 may be independently positioned, a variety ot input signals may be applied to start and stop the counting operation. Thus with the start selector switch 52 in the make position and with the stop selector switch 53 in the |pulse position, the interval to be time-d is started by the closing of an external circuit connected across the start terminals 2l and stopped by a positive pulse applied to the stop terminals 22 since such inputs are effective, respectively, to .lire tirst g. s tube Si) which starts the counting operation by unblocking diode 3u followed by the tiring or gas tube 39 which again blocks diode 30 to stop the counting operation.

When it is desired to cumulatively measure a number of successive time intervals, either ehe start selector switch 52 or the stop selector switch 53 may be operated to the cumulative plus or the cumulative make positions. With either of these selector switches in `the Cum. -l-

position, the apparatus will cumulatively measure the length of all successive time intervals during which a positive signal is applied to the corresponding input terminals. With either selector switch in the CM position, all intervals during which an external circuit shunts the corresponding input terminals will be cumulatively registered upon the decade counters.

lf the start selector switch 52 is operated to either the Cum. or Cum. make positions, the start gas tube Sti is immediately fired so that the recording of pulses from the pulse source 14 upon the decade counters is subject only to the application of the corresponding positive signal or short circuit to the start input terminals. This result is accomplished by the connection provided through contact 80 of the start selector switch 52 which connects the lower terminal of resistor 67 to ground so as to remove the negative bias from the control grid of gas tube 50 and permit this tube to tire. The cumulative counting may be terminated either by removing the distinctive signal which identifies the successive intervals or by operation of the stop gate control 12 which may be independently operated at any time in response to a proper signal applied to the stop input. If, however, the cumulative control is to be obtained by operation of the stop selector switch 53 to either the Cum. -lor Cum. make position, the start control gas tube 50 is not tired. As a result, the measuring of successive time intervals cannot take place until a proper start signal has been applied to the start input terminals to make start control tube 50 conductive. For example, with the stop selector switch 53 in the Cum. -iposition, the start selector switch 52 may be operated to the -lposition. Under these circumstances, at the beginning of a succession of intervals to be timed, a positive pulse must be applied to the start input and all following intervals during which a positive signal is applied to the stop input will be cumulatively recorded on the decade counters with the timing stopped only when the positive signal is no longer applied to the stop input.

For the cumulative timing of intervals, the control of the input to the decade counters is accomplished through tubes 28 and 81 included in the cumulative gate control 18. When neither the start selector switch 52 nor the stop selector switch 53 is in the Cum. -lor Cum. make position, no voltage is applied to the plate of tube Si. Consequently, tube 28 is cut ol by the negative grid bias supplied from through resistor 83. According to the description already given, with the tube 28 cutot, it acts as a high impedance shunt for tube 25 so that the pulses from the pulse source i4 are not blocked. However, when either the start selector switch 52 or the stop selector switch 53 is moved to the Cum. or Cum. make positions, a connection is provided through either contact 77 or 82 respectively to energize the plate of tube 81 from the (-1-) voltage source. Without the proper signal applied to either the start input or stop input, tube 81 is cut oli because of the xed cathode bias supplied by the voltage dividing network including resistors 87 and 8S connected between and ground. As a result, the plate voltage of tube 81 is high and increases the grid-cathode voltage of tube 23 above cutolf. Tube 28, therefore, conducts and acts as a low impedance shunt across tube 25 so that the pulses from the pulse source are blocked.

With either of the selector switch in the Cum. -lposition and the proper positive voltage applied to the corresponding input terminals, the increase of voltage at the control grid of tube Si causes this tube to conduct, and the resulting decrease ot its plate voltage causes tube 28 to become cut on?. As a result, during the time that this positive signal is applied, the output pulses of the pulse source 14 are not blocked and are applied through the counter gate 13 to the units counter l5. it should be remembered, however, that when the positive signal is applied to the stop input and the stop selector tu? switch 53 is in the Cum. -I- position, the start gas tube 56 must still be fired by an appropriate signal applied to the start terminals 21 before any timing action can take place. When the positive signal is applied to the start inptut, however, with the start selector switch 52 in the proper position, the start control gas tube will already have been fired so that a start signal will not be required. Under these circumstances, the timing action may be stopped at any time independently by applying a proper signal to the stop terminals 22 with the stop selector switch 53 in the proper position. Resistor 89 in the grid circuit of tube 81 permits relatively large input signals to be applied to the input terminals for Cum. -loperation Without allowing the control grid to be driven substantially positive with respect to the cathode.

When either the start selector switch 52 or the stop selector switch 53 is operated to the Cum. make position, the cathode of tube 8l. is connected through either contact 54 or contact 85 and thus through the corresponding resistor 76 and S respectively to ground. The cathode of tube 8l is normally placed at some positive potential by means of the connection from through resistor 87, and through the cathode resistor 88 and either resistor 76 or 86 in the input switching circuits to ground. In this condition, tube 8l is cut off so that tube 28 conducts and blocks the pulses from the pulse source 14. However, when the required short circuit is applied to the corresponding start or stop input terminals, the cathode of tube 81 is connected to ground so that the gridcathode voltage becomes less negative and tube 8l becomes conductive. Tube 28, as a result, becomes nonconductive so that the pulses from the pulse source i4 are no longer blocked. The result then is that during the time the short circuit is applied to the proper input terminals, the interval throughout which such short circuit is applied is measured on the decade counters.

The reset contacts 19 include the contacts 33 and 9i) operated by the reset-test switch 74. When an interval is to be timed, contact 33 is in the normal position so that voltage from (-l-) is applied to the plates of tubes 5@ and 35 and also from the plate of tube 35 to the plate of gas tube 39. Prior to each measuring of a time interval, the reset-test switch 74 is operated to the reset position momentarily. Movement of contact 33 to this position removes the high potential from gas tubes 5t) and 39 and tube 35. As a result, the gas tubes 39 and 50 are both restored to the normal nonconductive condition, thereby conditioning the apparatus for the beginning of a new timing operation. Contact 90 of the reset-test switch 74 is associated with the resetting of the various decade counters to the zero condition at the end of a timed interval, and its etect will more fully be described later. Additional contacts of the reset-test switch may be provided as shown in the block diagram of Fig. 2 to control the operation of a relay whose operating characteristics are to be timed.

Fig. 3B illustrates a typical decade counter as used for the units counter l5, tens counter 16, and hundreds counter i7. This counter is of the binary type, employing four dual-triode, flip-op circuits so that it is ordinarily capable of counting 24 or 16 counts. By means of a feedback organization, this counter is adapted to count only l0 input pulses, thereby permitting decade counting. Briefly, this is accomplished by advancing each decade counter two counts when the fourth input pulse is applied to it and advancing it another 4 counts when the sixth input pulse is applied to it so that by the time the tenth input pulse is applied, all the steps of the counter are restored to the normal condition. Restoration of the last stage of the units counter l5 to its normal condition occurs when the tenth input pulse is applied and causes a single input pulse to be applied to the tens counter i6. Similarly, when the last stage of the tens counter 16 is restored toits normal condition on each Consequently, the third stage is quickly restored to the condition it previously had so that its left-hand tube again assumes the nonconductve condition with its righthand tube conductive. This feedback is designated as feedback B in Fig. 4. This feedback has the effect of advancing the count by four as the conditions of the four stages are then as they would be for a count of twelve if feedback were not employed. Fig. shows that the third stage is operated to its normal condition upon the occurrence of the sixth pulse only for a limited time because the pulse fed back from the fourth stage quickly operates it again Vfrom the normal condition. Therefore, at the time of occurrence of this sixth input pulse, the plate voltage of the right hand tube of the third stage increases and then again quickly decreases. The resulting variation of potential of the right-hand tube of the third step appears, in effect, as a narrow positive pulse. Since the duration of this positive pulse is small as compared to the time constant of the feedback network to the preceding stage, differentiation of the trailing edge of this pulse does not produce a negative pulse of sutilcient amplitude at the control grid of the left-hand tube oi the second stage to operate this second stage from the normal condition The various stages of the counter respond in the usual manner to the seventh, eighth, and ninth input pulses, and at the tenth input pulse all of the stages are operated to the normal condition which is equivalent to a reset of the counter to zero. The restoration of the last stage to the normal condition causes a pulse to be fed to the tens counter 16. Thus, for each tenth pulse counted by the units counter 15, a single pulse is applied to the first stage of the tens counter 16. In this way, the input pulses to the counters may be decimally recorded, thereby permitting the number of pulses counted to be readily interpreted.

As already described, the input pulses to each stage of the counter are applied to the control grids of both tubes in such stage through individum resistance-capacitance combinations. Thus, the input pulses to the second stage of the units counter 15 obtained from the grid of the right hand tube of the preceding stage are applied through condenser 120 and resistor 121 to the grid of tube 100 and also through condenser 122 and resistor 123 to the grid of tube 114. Such an input circuit organization permits the voltage at the grids of tubes 10S and 11d to respond properly to the variations in potential at the grid of tube 92, yet effectively isolates the control grids of tubes 108 and 114 from pulses which might be fed back from the third stage of the counter over the coupling wire 124 connecting the second and third stages. Thus, when the second stage is operated from one to the other of its two stable conditions, the changes in plate voltages of tubes 108 and 114 cause corresponding changes in the voltages at the grids of these tubes. These grid voltage changes encounter high impedances in the R-C coupling circuits including condenser 120 and resistor 121 associated with tube 103 and the corresponding condenser 122 and resistor 123 associated with tube 111i. As a result, these grid voltage variations are greatly attenuated and can have but little effect upon the tubes S51 and 92 of the previous stage.

Ten neon lamps are associated with each decade counter such as the units counter 15. A single lamp among the ten provided for each counter is energized at any time so that, when three counters such as the unitscounter 15, tens counter 16, and hundreds counter 17 are used, a visual indication of the number of pulses counted up to and including 999 is provided.

The neon lamp corresponding to each even-numbered count has one terminal connected to bus 100, and one terminal of each lamp for the odd-numbered counts is connected to bus 101. Bus 100 is connected to the junction of the plate load resistors 102 and 103` of tube 92. Similarly, bus 101 is connected to the junction of the plate load resistors 104 and 10S of tube 91. The re'- maining terminal of each neon lamp is connected through suitable decoupling resistors to the plates of two tubes included in the three stages of the counter following the first stage. For example, the lower terminal of neon lamp 106 provided for the zero count is connected through decoupling resistor 107 to the plate of tube 108 and also through decoupling resistor 109 to the plate of tube 110. Similar connections are provided for the remaining neon lamps.

Fig. 3 shows that the first stage of the counter is in the normal condition only for each even-numbered count. Therefore, during each even-numbered count, tube 92 is nonconductive so that a high voltage appears on bus 100. For each odd-numbered count, this iirst stage is in the opposite condition so that bus 101 is at a relatively high potential. With the upper terminal of each even-nurnbered lamp at a high potential for an even count, it is only required that the potential at the lower terminal of the proper lamp be sufciently reduced upon the correspondingly even numbered count to cause the neon bulb to conduct and become illuminated. Fig. 3 shows that the second and fourth stages of the counter are both in their normal condition prior to the reception of the first count. Therefore, tubes 108 and 110 are both conductive at this time so that the voltage at the lower terminal of neon lamp 106 is at a low potential. This voltage level at the lower terminal of lamp 106 is suliiciently lower with respect to the relatively high potential on bus at this time to permit this lamp 106 to pass current and be illuminated. When this first input pulse is applied to the counter, the condition of the first stage is reversed so that the potential at bus 100 decreases. Even though tubes 108 and 110 remain conductive so that the potential at the lower terminal of lamp 106 is not changed, the decrease of voltage on bus 100 causes the lamp 106 to be unilluminated because there is now not a suiiicient potential difference across the terminals of this lamp to cause it to conduct current. The lower terminal of lamp 111 is at the same potential as the corresponding terminal of lamp 106, but with bus 101 now at a high potential this lamp 111 becomes illuminated, thereby indicating that one pulse has been counted.

When the second input pulse is received by the counter, the potential of bus 101 is lowered to extinguish lamp 111 and the potential of bus 100 is now increased to a a relatively high value. The lower terminals of lamps 112 and 113 are connected through suitable decoupling resistors to the plates of tubes 114 and 115. Fig. 3 shows that the second stage of the counter has been operated from its normal condition by the second input pulse, whereas the third stage is still in its normal condition with tube 115 conductive. Both tubes 114 and 115 are conductive at this time so that the voltage at the lower terminal of lamp 112 is suiciently low with respect to the high voltage now appearing on bus 100 so that this lamp 112 can now be illuminated. In a similarmanner, the voltages at the terminals of the various neon lamps are selectively varied to permit one lamp at a time to be illuminated.

Buses 100 and 101 are connected to the junctions of series-connected load resistors provided in the plate circuits of tubes 91 and 92. By connecting these buses at these points instead of directly to the plates of tubes 91 and 92, the lower limits of the voltages appearing alternately on buses 100 and 101 are increased. The reason for providing such an arrangement is to prevent one of the neon lamps from becoming illuminated improperly. For example, the voltage at the lower terminal of neon lamp 106 becomes relatively high when both tubes 10S and are nonconductive. If, at the same time, the voltage on bus 100 is made so low that the difference in potential exceeds the tiring potential of lamp 106, this lamp will then become illuminated. Therefore, by preventing the voltage on buses 100 and 101 from reaching l such a low level that the dilierence between `Such low voltage and the higher voltage at the other terminal of any of the lamps exceeds the tiring potential of these lamps, an erroneous indication is prevented.

The single-cumulative switch 84 provides a means for resetting both the start gate control il and the stop gate control 12 prior to each new timing operation Without causing a reset of the count then registered on the decade counters. This feature is desirable when the average duration of a number of successive intervals, each identilied at its beginning and end by a suitable signal applied to the start and stop input respectively, is t0 be determined. With switch 34 in the single position, the connection of bus 94 to the source is dependent only upon the position of contact 9d of switch 74. With switch S4 in the cumulative position, bus 94 remains connected to the source even if switch 74 is operated to the reset position for the purpose of restoring the start and stop gate controls to the normal condition. Consequently, the decade counters will not be reset to zero. rthis single-cumulative switch 34 may be operated independently of the setting of the start or stop selector switches 52 and which, as described, Vmay be operated to C-l- (cumulative plus) or CM (cumulative make) positions. in cumulatively timing a succession of intervals throughout which a distinctive signal is applied to the respective start or stop inputs, the start and stop gate controls are not operated for each such interval as has been described. To illustrate, ii the destinctive signal such as a positive voltage is applied to the stop input, the start gate control is independently operated by a separate signal when the timing is to begin. Thereafter, the start and stop gate controls are not operated and the time of each interval throughout which the positive signal is applied to the stop input is added to the time already registered on the counters. This example illustrates that the reset-test switch 74 need not be operated from the test position during such cumulative timing, and the single-cumulative switch 84 may therefore be left iu either position.

In actual practice, the features of this invention may be incorporated into an interval timer which may assume `any of several forms. Fig. 1 illustrates, merely by way of example, one possible way in which Vthe various switches, terminals, and indication lamps may be positioned upon the panel of the interval timer. The lamps associated with the various decade counters are located so as to be visible through corresponding holes in the front panel. The various switches such as the reset-test switch 74, pick rlp-drop away switch 73, the single-cumulative switch S4, etc. are also shown on this front panel. For various relay tests, energy is supplied as from a battery to the energy terminals 40, and the relay winding is then connected to the coil terminals 4l.

Having described an electronic interval timer as one specific embodiment of the present invention, it should be understood that this form is selected to facilitate in the disclosure of the invention rather Vthan to limit the nun.- ber oi forms which it may assume; kand it is to be further understood that various modilications, adaptataions, and alterations may be applied to the specic form shown to meet. the requirements of practice without in any manner departing from the spirit or scope of the present invention.

What l claim is:

l. In an interval timing organization, means for producinff a succession of pulses of a predetermined frequency, a counter for counting said pulses, a normally nonconductive start control gas discharge tube being etective when made conductive to cause said pulses to be applied to said counter, a normally nonconductive stop control discharge tube being eiieetive when made conductive to prevent said pulses from being applied to said counter, Vseparate control circuit means associated with each of said gas discharge tubes and each comprising, an electron tube having control grid and cathode and plate electrodes, a cathode circuit for said tube including a cathode resistor and means for applying a positive voltage to said cathode, iirst input circuit means for each electron tube including a rst coupling capacitor for applying an external circuit condition to said cathode resistor, second input circuit means associated with each electron tube including a second coupling capacitor for applying an external circuit condition to said control grid, switching circuit means associated with each control circuit means for adapting said control circuit means to be responsive to different external circuit conditions applied to respective input terminals, said switching circuit means in one position being elective to cause an external positive electrical pulse to be applied to said control grid of the associated electron tube and in its second position being effective to cause an external negative pulse to be applied to said cathode of said tube, said switching circuit means in its third position being effective to connect said control grid through its associated coupling capacitor to a source of positive potential and connecting said second input circuit means to said input terminals to thereby condition said control circuit means to be responsive to the breaking of an external circuit, said switching circuit means in its fourth position being effective to connect said cathode through its associated coupling capacitor to a source of positive potential and connecting said first input circuit means to the associated input terminais to thereby condition said control circuit means to be responsive to the closure of an external circuit, each external circuit condition being effective to cause a momentary increase in plate current of said associated electron tube, and means responsive to the increased plate current of said electron tube to make the associated gas tube conductive, whereby said pulses are applied to said counter only during the interval initiated by the application of distinctive start and stop inputs to the respecive input terminals.

2. A testing device for measuring time intervals including, means for producing electrical pulses uniformly spaced and of a selected frequency, counting circuit means for counting said pulses, start control circuit means, stop control circuit means, each of said start and said stop control circuit means including an electron discharge gate control tube selectively operable between distinctive conductive and nonconductive conditions, start and stop input terminals associated respectively with said start and stop control circuit means, an input tube associated with each gate control tube and adapted to distinctively respond to external signals applied to said start and said stop input terminals and indicative of the beginning and end respectively of each interval to be timed, separate start and stop switching circuit means for connecting said start and said stop input terminals to the control grid and cathode selectively of the corresponding input tube, each or" said input tubes thereby having its plate-cathode current varying in the same direction for both positive and negative polarity of input pulses applied to said input terminals and alternatively also in response to the closing or opening of an external circuit connected across said terminals, means responsive to the varying of the plate-cathode current of said input tube in said selected direction to operate the associated gate control tube from its normal condition to its other distinctive condition, and circuit means governed jointly by said start and said stop gate control tubes and being effective to supply said timing pulses to said counting means only during the interval between the successive operations of said start and said step gate control tubes respectively from their normal conditions to their opposite distinctive conditions.

3. in an interval timer, a source of regularly occurring electrical pulses having a predetermined frequenc a rst electron tube having said pulses applied to its control grid, circuit means for connecting the plate of said iirst tube through a load resistor to a source of positive potential,

I :a second grid controlled electron tube having its plate connected to the plate of said iirst tube, control circuit means associated with said second tube and being continuously effective to normally provide a grid-cathode bias for said tube tending to make said second tube conductive, input circuit means including a pair of input terminals for applying a single distinctive external signal whose duration corresponds to the interval to be timed to said control circuit means, said control circuit means being governed by said distinctive external signal to vary said grid-cathode bias of said second tube to cause said second tube to become nonconductive only throughout the time said single distinctive external signal is applied to said input terminals, a counter responsive to the pulses appearing at the plate of said rst electron tube, whereby said second tube when in its normally conductive position is effective to shunt the plate-cathode circuit of said rst tube thereby References Cited in the file of this patent UNITED STATES PATENTS 2,332,300 Cook Oct. 19, 1943 2,395,127 Kornei Feb. 19, 1946 2,401,747 Dibblee June 11, 1946 2,405,597 Miller Aug. 13, 1946 2,422,698 Miller June 24, 1947 2,528,394 Sharpless Oct. 31, 1950 2,566,078 Bliss Aug. 28, 1951 2,575,759 Higinbotham Nov. 20, 1951 2,604,263 MacSorley July 22, 1952

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