CA1053343A - Electrical data collecting device - Google Patents
Electrical data collecting deviceInfo
- Publication number
- CA1053343A CA1053343A CA248,270A CA248270A CA1053343A CA 1053343 A CA1053343 A CA 1053343A CA 248270 A CA248270 A CA 248270A CA 1053343 A CA1053343 A CA 1053343A
- Authority
- CA
- Canada
- Prior art keywords
- transmitter
- transmitters
- sensor
- timer
- transmission line
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- G—PHYSICS
- G08—SIGNALLING
- G08C—TRANSMISSION SYSTEMS FOR MEASURED VALUES, CONTROL OR SIMILAR SIGNALS
- G08C15/00—Arrangements characterised by the use of multiplexing for the transmission of a plurality of signals over a common path
- G08C15/06—Arrangements characterised by the use of multiplexing for the transmission of a plurality of signals over a common path successively, i.e. using time division
- G08C15/12—Arrangements characterised by the use of multiplexing for the transmission of a plurality of signals over a common path successively, i.e. using time division the signals being represented by pulse characteristics in transmission link
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Arrangements For Transmission Of Measured Signals (AREA)
- Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)
Abstract
ABSTRACT
This invention relates to data transmission system of the type where a plurality of transmitters are located at a location remote from a receiver and are adapted to transmit information from their location in turn to the receiver. The transmitters in the case of this invention are each self-powered and have their own trans-mitter timer associated with them. They are all set to operate from time zero by a master timer and their individual power sources are recharged for the power dissipated in each of their transmissions by a charging pulse that is received over the transmission line.
The resetting of the transmitter timers to cause them to transmit in sequence is done during the recharging period which follows the transmissions of the series of transmitters.
This invention relates to data transmission system of the type where a plurality of transmitters are located at a location remote from a receiver and are adapted to transmit information from their location in turn to the receiver. The transmitters in the case of this invention are each self-powered and have their own trans-mitter timer associated with them. They are all set to operate from time zero by a master timer and their individual power sources are recharged for the power dissipated in each of their transmissions by a charging pulse that is received over the transmission line.
The resetting of the transmitter timers to cause them to transmit in sequence is done during the recharging period which follows the transmissions of the series of transmitters.
Description
This invention relates to digital data transmitters : of the time division multiplex type which are configured onto a single pair of wires.
Data transmitters of this general type are commonly used to collect data from widespread locations on a single data telephone line. They could, for example, be used in the measurement and `~
collection of data related to petrochemical products stored in tanks on tank farms. The transmitters could transmit information on the level of product in a tank, the temperature of product in a tank and the pressure in a tank. In such a use, transmitters with sensors would be mounted at each tank and the output of the sensors is fed ; to the transmitters for transmission over a single dataline to a . remote receiving station where it is decoded and read out.
In the usual installation of this type, there is a plur- tality of data transmitters each of which has a receiver associated therewith that receives a signal over the dataline from a central transmitting station to dictate the transmission period o~ the individual transmitters whereby the plurality of transmitters trans-mit over the data line to the remote receiver each after the other as polled by the central transmitting:station. The provision of a receiver for each transmitter to control its transmission period is costly and cumbersome.
It has been found that the costly and cumbersome practice of providing a receiver to control the transmission sequence of the ~;;
transmitters over the dataline can be avoided by the use of a simple 1..
timing device adjacent to the transmitters that is set from a central ;';: : ~
location to cause the transmitters to transmit~ in turn, each after . .
the other, in a pre-determined sequence. .:
An electrical data transmittlng system according to this .
invention has a plurality of transmitters each having a rechargeable . . -:
''.: :
:, '' '' ~33~3 power source, each having at least one sensor with its output connected to the input of its respective transmitter, and each .:~
having a transmitter timer; a data transmission line; a receiver to receive signals transmitted over said data transmission line; .` .
a master timer; a rechar~eable voltage source connectable to said ~.
transmission line to simultaneously recharge the rechargeable power source of each of said transmitters; said transmitters being normally not connected to the ~ransmission line for transmission; means for simultaneously setting the transmitter timer of each o~ said trans-mitters to connect its respective transmitter to the data transmission line whereby the plurality of transmitters are connected one at a time and in predetermined time sequence to the data transmission line for transmission; said transmitters when connect~d for transmission to said transmission line each being adapted to transmit information about their location and the output o:E their respective sensors to ..
said receiver; said master timer being cyclically operable to dictate connection of said recharging voltage source to said trans-mission line for a predetermined time to recharge the rechargeable power source as aforesaid, in the time interval following sequential 20 data transmission by said plurality of said transmitters as afore- ;~
said; said means ~or simultaneously setting said transmitter timers being responsive to operation of said master timer during said time interval following data transmissien to set the transmitter timer of .:
each of said transmitters as aforesai.d. The invention will be clearly understood after reference to the follow.ing detailed speciic~tion read~.
in conjunction with the drawings.
In the drawings: :
Figure 1 is a lock diagram illustration of a data t.rans-mittirlg system showing three transmitters;
Figure 2 is a graph illustrating the sequential trans-mission of the three transmitters;
~533~3 Figure 3 is a schematic illustration of three sensors o~ a transmitter;
~ igure 4 is a schematic illustration of the temperature sensor;
Figure 5 is a schematic illustration of the pressure sensor; and Figure 6 is an illustxation of a transmitter mounted on the side of a storage tank.
Figure l is a schematic illustration of a data transmitting system showing three ~ransmitters lO and a receiver 12 for the trans-mitters on a transmission line, generally indicated by the numeral 14. Each of the transmitters has its own rechargeable battery source of power which, in uset is recharged over the transmission line 14 with power from the power supply ~6 as dictated by the operation of a master timer 18 ~s will be explained later.
Each transmitter is further connected to three sensing devices 20, 22 and 24. Thase devices have electrical outputs that :; , . .
can be transmitted by the transmitter over the transmission line. ~;
Each transmitter further has its own quartz crystal controlIed timer clock 26. These timer clocks are settable to connect their respective transmi~ter ~o the data transmission line ~or transmission in a predetermined time sequence wherein each of the transmitters is connected to the line in turn, one at a time, to transmit the output of its respective sensing devices to the receiver.
After each of the transmitters has been connected to the tran~mission line by it~ respective timer to transmit the output of `~
its respective sensing devices, a master time 18 operates circuit j;
breaker 28 to connect voltage source 16 to the transmission line and to the rechargeable battery power sources of the transmitters for a short period of time to permit a charging pulse of current to ~flow to the rechargeable nicad battery power sources of the trans-mittexs and recharge them for the power used in the transmission.
.
i3~3 The recharging pulse also acts to reset the timer clocks 26 of the transmitters to control the next ollowing transmission of data from the transmitters to the receiver 12.
The transmitters lO transmit their message with an output that consists of bipolar pulses. They are square wave generated but, in practice, round off into a general saw-toothed configuration in the process of transmission. Pulses having a generated amplitude - of about 7 volts have been found satisfactory. The width of the pulse at the base is equal to the width of the space between pulses~
Pulses have one polarity for binary "1" and ~he o~hex polari~y for binary "0"0 As indicated, the transmitters lO are connected to the data transmission line 14 for transmission one at a time and in time sequence by the quart2 crystal timer clocks 26 and after each trans-mitter has transmitted its data once, it ceases to transmit, dis-connects its driver from the communication line and tramsmits nothing further until its clock is reset by the recharging pulse. There is a cyclic transmission of data from the transmitters 10, each trans-mitting in serial arrangement.
The transmission of each transmit~er consists of forty digltal pulses or bits designated as a word. As indicated, each of the transmitters transmits in turn and the words of the three transmitters constitute a sentence. In the Example of this in-vention described herein, the transmitters 10 transmit a forty bit word which has the following composition:
First eight bits transmitter address Next eight bits input to transmitter from sensor 20 Next eight bits input to transmitter from sensor 22 Next sixteen bits input to transmitter from sensor 24 A quiet period of eight bits length precedes data trans-mission from each transmitter and a quiet period of sixteen bits -4- `
.:
. .
... . . .. . .
~V~;33~3 follows data transmission from each transmitter. Thus, each trans-mitter r~quires sufficient time for sixty-four bits to transmit its forty bit word. The timing of the quiet periods and the connection of the transmitters to ~he transmission line for trans-mission is controlled by the timer of the individual transmitters.
Thus, the timer clock 26 of the first transmitter operates to provi~e a quiet period of eight bits during which the transmitter output driver is conr.scted to the communication line and establishes a low impedence clamp 50 as to ensure minimum noise pick up immediately prior to the transmission o~ data. Following the quiet period, it connects its transmitter to the transmission line to transmit its address, the output of sensor 20, the output of sensor 22 an~ the ..~ . . :.
output of sensor 24. Following the completi~n of the transmission and the provision of the sixteen bit quiet period, it disconnects ; -its transmitter from the transmission line. Then, the timer of the second transmitter controls its ~ransmitter through a similar sequence foIlowing which the timer of the third transmitter controls its transmitter through a similar sequence and when the third and last transmitter has transmitted, the master timer 18 operates to connect the voltage source 16 to the transmission line to rechar~e the battery power sources of each of the transmitters. I'he re-charging cycle is for a predetermined time in the nature of a few seconds depending upon the design of the units and their requirement ~i for recharging.
As indicated upon recharging the timers are reset to cause their reSpective transmitters to transmit in turn following termina-tion of the rechargin~ cycle and aisconnection of the recharging source from the transmission line. ;
It has been found quite practical to recharge the battery '` -power sources for between 50 and 100 transmitters vver a standard transmission line.
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~, 5i3~
The peak pulse battery charging current that rnust becarried by the tran~mission line is a function of the bit rate and the number of transmitters on the line and it has been calculated that, for a data transmission speed of 8,000 bits per second and 250 micro power logic transmitters 10 on the line, will result in a peak pulse battery charging current of about 1.5 amperes over a recharging interval of about one second. This current can be handled by reasonable ~ransmission wire sizes. These circumstances of bit rate and transmitter numbers are, however, extreme and most common installations will involve a bit rate in he order of 500 bits per second and less than S0 transmitters. Thus, most practical situations are well below the extreme situation that has been found to be within the limits dictated by reasonable transmission wire sizes.
The transmitters 10 are standard three state transmitters and the numerals 30, 32 and 34 reer to the breaker contacts~
Numeral 36 refers to an isolator that will pass only the hiyher 2~
volt recharging current pulse from the voltage 16 to the batteries of the transmitters. Crystal clocks 26 which control the operation of their respective transmitters 10 are reset during the time interval between sentences by pa~sage of current throu~h the isolators 36.
Figure 2 is a time base graph illustrating the connection of the transmi~ters 10 to the line 14 under control of their respective clocks 26. Time has been indicated in digital indications of the transmitter outputs, i.e., bits. In this illustration, a line indicating ~he aonnection of each transmit~er to ~he line during the transmission of a sentence has been indicated. The open condition of the transmitter in each case is indicated by the lower line and under this condition, each of the breakers 30, 32 and 34 ,, , is open and its respective transmitter is disconnected from the line.
The upper line indicate~ the other two conditions of the three state transmit~er~
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.
~ ~S33~3 ~11 transmitters are, as indicated, controlled by their ~`
respective timer clocks 26 which are simultaneously reset ~y the transmission of a recharging pulse from the charging source 16.
At the termination of the recharging pulse the first transmitter indicated by TI on the graph has its contacts 30, 32 and 34 closed.
This condition exists for a period of eight bits and provides a quiet period that precedes actual data transmission. Following a time lapse of eight bits, breaker 30 is ope~ed and breakers 32 and 34 remain closed under the cont~ol of the crystal clock 26. In this condition, the digital output of the transmitter is connected to the transmission line. The transmitter is operational and trans ;:.
mits its output to the receiver 12. - :.
The transmitter so connected to the line remains in this co~dition for 40 bits, i.e., to bit 48 on the time scale of the graph.
During this period, it transmits a wsrd of the transmitted sentence.
At the time of bik 48, the quartz clock of transmitter ;
1 again opera~es to close breaker 30 and all breakers are again in i~
the closed condition and the transmitter is shorted on the line. It ;~
remains in this condition for 16 bits, to bit 64 on the time graph.
At bit 64, the clock of transmitter 1 operates to open each breakers 30, 32 and 34 to entirely disconnect the transmitter TI from the line. Transmitter TI remains in this condition during the trans-mission periods of the other tran~mitters T2 and T3.
While transmitter 1 was either shorted across the line or operational on the line during the first 64 bits of the time scale, transmitters T2 and T3 were in the open circuit condition with each of their breakers in the open condition as indicated by their respective graphs. ~t the time of bit 64, the time clock of transmitter T2 operates to conduct it through a similar shorted and operational condition to that of ~ransmitter TI during the first 64 bits. At the time of bit 128, transmitter T2 ceases to transmit ~,.....
~533~L3 and each of its breakers are opened to disconnect it from the line.
As transmitter 2 is disconnected from the line, the driver of transmitter 3 is connected to the line by closure of its breakers 32 and 34 and it does through a similar 64 bit operation similar to transmitters Ti and T2 and specifically described for transmit~er TI.
At the termination of transmission of transmitter T3 all transmitters are disconnected from the communication line and await instruction.
This instruction takes the form of the applied xecharging voltage from voltage source 16 which is of a greater magnitude than --the transmitter output signals. In practice, a voltage of 24 volts has been used for recharging at;a -transmitting voltage of 7.
~ practical r~charging pulse using a bit rate of 500 bits per second will be of a duration of about 1500 bits. Following this, the transmittexsTI,T2 andT3transmit again as just described, under the dictation of their respective quartz crystal clocks which are each reset by the transmission of the recharging pulse over the line to cause the transmitters to transmit as just explained.
The sequence is repeated on a continuous basis.
The word of each transmitter in the Example given consists of the transmitter address and the inputs to the transmitter of each of the transmitker sensors. The timer for each transmitter controls the connection of the sen~ors for transmission to compose the trans-mitter word.
In a practical situation, there will, in most cases, be many more than three transmitters. The inventinn has been used to determine the pressure temperature and level of oil in storage tanks on a tanlc farm in which case a transmitter 10 is located on each oil storage tank and the s~stem continuously measures these quantities in each of the tanks on the farm. The receiver is v j ~.
, , ~ii33~3 located at a remote location and is pr~videcl with a computer to , give a continuous readout for each of the storage tanks on the ', farm. -Figure 3 is a schematic illustration of the sensors used in an oil storage tank and the data transmitter 10 for an individual oil storage tank. In Fi~ure 3, sensor 20 which senses the temperature of the oil within the tank has been genarally indicated by the numeral 20. It consists essentially of a resistance temperature device in a bridge circuit with an emplifier the output of whi~h is fed to an analogue to digital converter of '`
the transmitter to give a digital output that is transmitted over , ;
the transmission line during the appropriate eight bits of the 40 `,~ '~
bit word for the transmitter concerned. Figure 4 is a wiring illustration of the device. ~, The resistance temperature device 38 is immersed in the liquid oil within the storage tank and i5 electrically connected in a bridge circuit that includes constant curreint resistor 40 and ~, potentiometer ~2. The variable contact of thei potentiometer 42 is ';' used to calibrate the sensor. Voltage for the circuit is supplied ,~
20 from the transistor hattery source and the output of the circuit '' which varies with the temperature of the oil in the tank is supplied ,'~' to the operational amplifier 44. Power for amplifier 44 is also ta]cen from the transmitter battery power supply. ~,',' The out,put from the amplifier 44 is applied to an input ~'`
of the transmitter 10. In this r,espect, the output from the ,`
amplifier 44 is analogue and ~etransmitter includes an analogue to digital converter the output of which is fed to a storage device that stores the reciord of tempeirature as detected by the resistance temperature device 38 for transmission. "'~' ' This lnormation of the sensor 20 is transn~itted during the second 8 bits of the 40 bit word for its respective transmitter. '~
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With this inven~ion and the self-powered transmitter with its quartz clock controlled operation, current is circulated through the bridge circuit which contains the temperature sensing transducer only when an actual measurement i5 being ~aken. This is controlled by the clock for the paxticular transmitter to which the sensing device relates. It is a very short period of time and results in substantial advantages in u~e.
Resistance temperature devices are subject to error due -to internal heating from their own power supply. Because of this, they are normally used at very low output levels. With the self-powerad transmitter technique Of this invention, current is circula-ted through the measuring element for very short periods of time only.
Because of thi~, the average power dissipated in the measuring interval can be relatively high without beiny subject to internal heating. The achievement of this relatively high power results in a high signal output which is much easier to handle and less susceptible to noise than a low level signal output.
In a device already constructed, the resistance temperat-ure device 38 was powered during the first ei~ht bits of the trans-mission cycle when the transmi~.ter transmits its address to thereceiver. The result was stored and transmitted to the receiver during the second eight bits of the transmission period. Thus, through operation of the timer, the period during which the resistance temperature device is powered was substantially reduced and resulted in a high signal output and greatex accuracy.
The pressure is determined by sensor 22. Figure 5 is a schernatic illustra~Don of the operation of the pressure sensing device. It consists of ~ bellows 46, one side of which is exposed to the interior o the tank 48 and the other side of which is on the outside of the tank 48. The side of the bellows on the outside of the tank assumes a position that is responsive to variations of ~Q~ 3 pressure within the tank and there is a linka~e 50 from the outer side of the ~ank that has a dial ~2 that assumes a position related to the pressure. Dial 52 acts on a poteniometer 5A, the output of ;
which is fed to an input of the transmitter 10. The input has an analogue to digital conventer which converts the analogue electrical output from the potentiometer 54 to a digital output and stores it for transmission. The output of the pressure sensing device is transmitted during the third eight bit piece of the ~0 minute word of each transmitter. Potentiometer 54 is powered from the battery source of the transmitter but only during transmission period.
Pressure sensing devices and potentiometers are well known in the art and further detail is not thought necessary.
Level within the tank is det~rmined by sensor 24. ~his is achieved by float 56 connected by means o~ a tape to a take-up rell that is spring loaded and located in the housi~g of the device 60. The shaft from the reel adopts a position related to the level of the ~oat. Shaft encoders are well known in the art and further detail of the mechanical features of a shaft encoder are not thought necessary. The mechanical output o~ the shaft of the shaft encoder is applied to an electrical circuit that produces a digital output and which is transmitted during the last sixteen bit interval of each forty bit word of each transmitter. Power for the circuit is obtained from the power source of the transmitter~ ' The arrangement of the bits in a transmitted word is capable of great variation and does not form an essential part of the invention. However, as indicated, in the forty bit word trans-mitted from each of the teansmitters 10 with this invention, the first eight bits transmitthe location or address of the transmitter and identify the link. The second eight bits transmits the output of the temperature sensing device. The th~d eight bits transmit the instant output of the pressure sensing device and ~he last sixteen `~
bits transmits the instant output o~ the level sensing device.
~ ~i33~3 ~:
Figure 6 is a view of the lower portion of an oil storage tank showing an installation according to this invention. Numeral 24 refers to the shaft encoder which detects level. Numeral 22 refers to the pressure sensing device and numeral 20 refers to the temperature sensing device. l~hey are all connected to the trans~
mitter 10 which, as indicated, is housed within an explosion pxoof ho~ing~ The compactness of the installation is apparent from Fiyure 6.
In the system, all clocks are reset to real time zero by the reset pulse originating from the charging source and clock drift is only significant on a "per scan" basis.
The invention has been effectively used on an oil tank f~rm having about 14 oil storage tanks each fitted with a transmitter like the transmitter 10 with sensors for level, pressure and temperature as described and adapted to send a word having the composition described to a receiver at a remote central location.
The bit rate for transmission was 50~ bits per second. All trans-sistors had crystal clocks of standard design and there was no difficulty in achieving a .01~ stability. The words were trans-mitted at 24 bit intervals, as described above. The charging pulsewas 24 volts and had a duration of about 4 seconds.
~ 11 clocks were set to real time zero by the reset pulse originating from the receiver location so that clock drift was only significant on a per scan basis.
The pulses had a generated amplitude of about 7 volts, as described above. The signals received by the receiver were de-coded and fed through a computer of standard design to give a readout of pressure, temperature and level.
Each transmitter took a time period of 64 bits to transmit including the quiet periods at the beginning and end of its 40 bit word. Thus, the 14 transmitters took 896 bits to complete a sentence.
,~
The elapsed time for the 896 bi-ts was less than two seconds. A
recharging period of ~I seconds was used and -the total elapsed time fox transmission of all transmitters and recharging was rounded off at 6 seconds. The master timer was, therefore, set to connect and disconnect the recharging source at intervals o~ ~ seconds.
The ~xamples and quantities given are by way of example only and not to be construed in a restrictive way. ~he embodiments of the invention other than the ones illustrated will be apparent ~ .
to those skilled in the art. .:
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Data transmitters of this general type are commonly used to collect data from widespread locations on a single data telephone line. They could, for example, be used in the measurement and `~
collection of data related to petrochemical products stored in tanks on tank farms. The transmitters could transmit information on the level of product in a tank, the temperature of product in a tank and the pressure in a tank. In such a use, transmitters with sensors would be mounted at each tank and the output of the sensors is fed ; to the transmitters for transmission over a single dataline to a . remote receiving station where it is decoded and read out.
In the usual installation of this type, there is a plur- tality of data transmitters each of which has a receiver associated therewith that receives a signal over the dataline from a central transmitting station to dictate the transmission period o~ the individual transmitters whereby the plurality of transmitters trans-mit over the data line to the remote receiver each after the other as polled by the central transmitting:station. The provision of a receiver for each transmitter to control its transmission period is costly and cumbersome.
It has been found that the costly and cumbersome practice of providing a receiver to control the transmission sequence of the ~;;
transmitters over the dataline can be avoided by the use of a simple 1..
timing device adjacent to the transmitters that is set from a central ;';: : ~
location to cause the transmitters to transmit~ in turn, each after . .
the other, in a pre-determined sequence. .:
An electrical data transmittlng system according to this .
invention has a plurality of transmitters each having a rechargeable . . -:
''.: :
:, '' '' ~33~3 power source, each having at least one sensor with its output connected to the input of its respective transmitter, and each .:~
having a transmitter timer; a data transmission line; a receiver to receive signals transmitted over said data transmission line; .` .
a master timer; a rechar~eable voltage source connectable to said ~.
transmission line to simultaneously recharge the rechargeable power source of each of said transmitters; said transmitters being normally not connected to the ~ransmission line for transmission; means for simultaneously setting the transmitter timer of each o~ said trans-mitters to connect its respective transmitter to the data transmission line whereby the plurality of transmitters are connected one at a time and in predetermined time sequence to the data transmission line for transmission; said transmitters when connect~d for transmission to said transmission line each being adapted to transmit information about their location and the output o:E their respective sensors to ..
said receiver; said master timer being cyclically operable to dictate connection of said recharging voltage source to said trans-mission line for a predetermined time to recharge the rechargeable power source as aforesaid, in the time interval following sequential 20 data transmission by said plurality of said transmitters as afore- ;~
said; said means ~or simultaneously setting said transmitter timers being responsive to operation of said master timer during said time interval following data transmissien to set the transmitter timer of .:
each of said transmitters as aforesai.d. The invention will be clearly understood after reference to the follow.ing detailed speciic~tion read~.
in conjunction with the drawings.
In the drawings: :
Figure 1 is a lock diagram illustration of a data t.rans-mittirlg system showing three transmitters;
Figure 2 is a graph illustrating the sequential trans-mission of the three transmitters;
~533~3 Figure 3 is a schematic illustration of three sensors o~ a transmitter;
~ igure 4 is a schematic illustration of the temperature sensor;
Figure 5 is a schematic illustration of the pressure sensor; and Figure 6 is an illustxation of a transmitter mounted on the side of a storage tank.
Figure l is a schematic illustration of a data transmitting system showing three ~ransmitters lO and a receiver 12 for the trans-mitters on a transmission line, generally indicated by the numeral 14. Each of the transmitters has its own rechargeable battery source of power which, in uset is recharged over the transmission line 14 with power from the power supply ~6 as dictated by the operation of a master timer 18 ~s will be explained later.
Each transmitter is further connected to three sensing devices 20, 22 and 24. Thase devices have electrical outputs that :; , . .
can be transmitted by the transmitter over the transmission line. ~;
Each transmitter further has its own quartz crystal controlIed timer clock 26. These timer clocks are settable to connect their respective transmi~ter ~o the data transmission line ~or transmission in a predetermined time sequence wherein each of the transmitters is connected to the line in turn, one at a time, to transmit the output of its respective sensing devices to the receiver.
After each of the transmitters has been connected to the tran~mission line by it~ respective timer to transmit the output of `~
its respective sensing devices, a master time 18 operates circuit j;
breaker 28 to connect voltage source 16 to the transmission line and to the rechargeable battery power sources of the transmitters for a short period of time to permit a charging pulse of current to ~flow to the rechargeable nicad battery power sources of the trans-mittexs and recharge them for the power used in the transmission.
.
i3~3 The recharging pulse also acts to reset the timer clocks 26 of the transmitters to control the next ollowing transmission of data from the transmitters to the receiver 12.
The transmitters lO transmit their message with an output that consists of bipolar pulses. They are square wave generated but, in practice, round off into a general saw-toothed configuration in the process of transmission. Pulses having a generated amplitude - of about 7 volts have been found satisfactory. The width of the pulse at the base is equal to the width of the space between pulses~
Pulses have one polarity for binary "1" and ~he o~hex polari~y for binary "0"0 As indicated, the transmitters lO are connected to the data transmission line 14 for transmission one at a time and in time sequence by the quart2 crystal timer clocks 26 and after each trans-mitter has transmitted its data once, it ceases to transmit, dis-connects its driver from the communication line and tramsmits nothing further until its clock is reset by the recharging pulse. There is a cyclic transmission of data from the transmitters 10, each trans-mitting in serial arrangement.
The transmission of each transmit~er consists of forty digltal pulses or bits designated as a word. As indicated, each of the transmitters transmits in turn and the words of the three transmitters constitute a sentence. In the Example of this in-vention described herein, the transmitters 10 transmit a forty bit word which has the following composition:
First eight bits transmitter address Next eight bits input to transmitter from sensor 20 Next eight bits input to transmitter from sensor 22 Next sixteen bits input to transmitter from sensor 24 A quiet period of eight bits length precedes data trans-mission from each transmitter and a quiet period of sixteen bits -4- `
.:
. .
... . . .. . .
~V~;33~3 follows data transmission from each transmitter. Thus, each trans-mitter r~quires sufficient time for sixty-four bits to transmit its forty bit word. The timing of the quiet periods and the connection of the transmitters to ~he transmission line for trans-mission is controlled by the timer of the individual transmitters.
Thus, the timer clock 26 of the first transmitter operates to provi~e a quiet period of eight bits during which the transmitter output driver is conr.scted to the communication line and establishes a low impedence clamp 50 as to ensure minimum noise pick up immediately prior to the transmission o~ data. Following the quiet period, it connects its transmitter to the transmission line to transmit its address, the output of sensor 20, the output of sensor 22 an~ the ..~ . . :.
output of sensor 24. Following the completi~n of the transmission and the provision of the sixteen bit quiet period, it disconnects ; -its transmitter from the transmission line. Then, the timer of the second transmitter controls its ~ransmitter through a similar sequence foIlowing which the timer of the third transmitter controls its transmitter through a similar sequence and when the third and last transmitter has transmitted, the master timer 18 operates to connect the voltage source 16 to the transmission line to rechar~e the battery power sources of each of the transmitters. I'he re-charging cycle is for a predetermined time in the nature of a few seconds depending upon the design of the units and their requirement ~i for recharging.
As indicated upon recharging the timers are reset to cause their reSpective transmitters to transmit in turn following termina-tion of the rechargin~ cycle and aisconnection of the recharging source from the transmission line. ;
It has been found quite practical to recharge the battery '` -power sources for between 50 and 100 transmitters vver a standard transmission line.
S
~, 5i3~
The peak pulse battery charging current that rnust becarried by the tran~mission line is a function of the bit rate and the number of transmitters on the line and it has been calculated that, for a data transmission speed of 8,000 bits per second and 250 micro power logic transmitters 10 on the line, will result in a peak pulse battery charging current of about 1.5 amperes over a recharging interval of about one second. This current can be handled by reasonable ~ransmission wire sizes. These circumstances of bit rate and transmitter numbers are, however, extreme and most common installations will involve a bit rate in he order of 500 bits per second and less than S0 transmitters. Thus, most practical situations are well below the extreme situation that has been found to be within the limits dictated by reasonable transmission wire sizes.
The transmitters 10 are standard three state transmitters and the numerals 30, 32 and 34 reer to the breaker contacts~
Numeral 36 refers to an isolator that will pass only the hiyher 2~
volt recharging current pulse from the voltage 16 to the batteries of the transmitters. Crystal clocks 26 which control the operation of their respective transmitters 10 are reset during the time interval between sentences by pa~sage of current throu~h the isolators 36.
Figure 2 is a time base graph illustrating the connection of the transmi~ters 10 to the line 14 under control of their respective clocks 26. Time has been indicated in digital indications of the transmitter outputs, i.e., bits. In this illustration, a line indicating ~he aonnection of each transmit~er to ~he line during the transmission of a sentence has been indicated. The open condition of the transmitter in each case is indicated by the lower line and under this condition, each of the breakers 30, 32 and 34 ,, , is open and its respective transmitter is disconnected from the line.
The upper line indicate~ the other two conditions of the three state transmit~er~
'~
.
~ ~S33~3 ~11 transmitters are, as indicated, controlled by their ~`
respective timer clocks 26 which are simultaneously reset ~y the transmission of a recharging pulse from the charging source 16.
At the termination of the recharging pulse the first transmitter indicated by TI on the graph has its contacts 30, 32 and 34 closed.
This condition exists for a period of eight bits and provides a quiet period that precedes actual data transmission. Following a time lapse of eight bits, breaker 30 is ope~ed and breakers 32 and 34 remain closed under the cont~ol of the crystal clock 26. In this condition, the digital output of the transmitter is connected to the transmission line. The transmitter is operational and trans ;:.
mits its output to the receiver 12. - :.
The transmitter so connected to the line remains in this co~dition for 40 bits, i.e., to bit 48 on the time scale of the graph.
During this period, it transmits a wsrd of the transmitted sentence.
At the time of bik 48, the quartz clock of transmitter ;
1 again opera~es to close breaker 30 and all breakers are again in i~
the closed condition and the transmitter is shorted on the line. It ;~
remains in this condition for 16 bits, to bit 64 on the time graph.
At bit 64, the clock of transmitter 1 operates to open each breakers 30, 32 and 34 to entirely disconnect the transmitter TI from the line. Transmitter TI remains in this condition during the trans-mission periods of the other tran~mitters T2 and T3.
While transmitter 1 was either shorted across the line or operational on the line during the first 64 bits of the time scale, transmitters T2 and T3 were in the open circuit condition with each of their breakers in the open condition as indicated by their respective graphs. ~t the time of bit 64, the time clock of transmitter T2 operates to conduct it through a similar shorted and operational condition to that of ~ransmitter TI during the first 64 bits. At the time of bit 128, transmitter T2 ceases to transmit ~,.....
~533~L3 and each of its breakers are opened to disconnect it from the line.
As transmitter 2 is disconnected from the line, the driver of transmitter 3 is connected to the line by closure of its breakers 32 and 34 and it does through a similar 64 bit operation similar to transmitters Ti and T2 and specifically described for transmit~er TI.
At the termination of transmission of transmitter T3 all transmitters are disconnected from the communication line and await instruction.
This instruction takes the form of the applied xecharging voltage from voltage source 16 which is of a greater magnitude than --the transmitter output signals. In practice, a voltage of 24 volts has been used for recharging at;a -transmitting voltage of 7.
~ practical r~charging pulse using a bit rate of 500 bits per second will be of a duration of about 1500 bits. Following this, the transmittexsTI,T2 andT3transmit again as just described, under the dictation of their respective quartz crystal clocks which are each reset by the transmission of the recharging pulse over the line to cause the transmitters to transmit as just explained.
The sequence is repeated on a continuous basis.
The word of each transmitter in the Example given consists of the transmitter address and the inputs to the transmitter of each of the transmitker sensors. The timer for each transmitter controls the connection of the sen~ors for transmission to compose the trans-mitter word.
In a practical situation, there will, in most cases, be many more than three transmitters. The inventinn has been used to determine the pressure temperature and level of oil in storage tanks on a tanlc farm in which case a transmitter 10 is located on each oil storage tank and the s~stem continuously measures these quantities in each of the tanks on the farm. The receiver is v j ~.
, , ~ii33~3 located at a remote location and is pr~videcl with a computer to , give a continuous readout for each of the storage tanks on the ', farm. -Figure 3 is a schematic illustration of the sensors used in an oil storage tank and the data transmitter 10 for an individual oil storage tank. In Fi~ure 3, sensor 20 which senses the temperature of the oil within the tank has been genarally indicated by the numeral 20. It consists essentially of a resistance temperature device in a bridge circuit with an emplifier the output of whi~h is fed to an analogue to digital converter of '`
the transmitter to give a digital output that is transmitted over , ;
the transmission line during the appropriate eight bits of the 40 `,~ '~
bit word for the transmitter concerned. Figure 4 is a wiring illustration of the device. ~, The resistance temperature device 38 is immersed in the liquid oil within the storage tank and i5 electrically connected in a bridge circuit that includes constant curreint resistor 40 and ~, potentiometer ~2. The variable contact of thei potentiometer 42 is ';' used to calibrate the sensor. Voltage for the circuit is supplied ,~
20 from the transistor hattery source and the output of the circuit '' which varies with the temperature of the oil in the tank is supplied ,'~' to the operational amplifier 44. Power for amplifier 44 is also ta]cen from the transmitter battery power supply. ~,',' The out,put from the amplifier 44 is applied to an input ~'`
of the transmitter 10. In this r,espect, the output from the ,`
amplifier 44 is analogue and ~etransmitter includes an analogue to digital converter the output of which is fed to a storage device that stores the reciord of tempeirature as detected by the resistance temperature device 38 for transmission. "'~' ' This lnormation of the sensor 20 is transn~itted during the second 8 bits of the 40 bit word for its respective transmitter. '~
,':
_g_ ,.
With this inven~ion and the self-powered transmitter with its quartz clock controlled operation, current is circulated through the bridge circuit which contains the temperature sensing transducer only when an actual measurement i5 being ~aken. This is controlled by the clock for the paxticular transmitter to which the sensing device relates. It is a very short period of time and results in substantial advantages in u~e.
Resistance temperature devices are subject to error due -to internal heating from their own power supply. Because of this, they are normally used at very low output levels. With the self-powerad transmitter technique Of this invention, current is circula-ted through the measuring element for very short periods of time only.
Because of thi~, the average power dissipated in the measuring interval can be relatively high without beiny subject to internal heating. The achievement of this relatively high power results in a high signal output which is much easier to handle and less susceptible to noise than a low level signal output.
In a device already constructed, the resistance temperat-ure device 38 was powered during the first ei~ht bits of the trans-mission cycle when the transmi~.ter transmits its address to thereceiver. The result was stored and transmitted to the receiver during the second eight bits of the transmission period. Thus, through operation of the timer, the period during which the resistance temperature device is powered was substantially reduced and resulted in a high signal output and greatex accuracy.
The pressure is determined by sensor 22. Figure 5 is a schernatic illustra~Don of the operation of the pressure sensing device. It consists of ~ bellows 46, one side of which is exposed to the interior o the tank 48 and the other side of which is on the outside of the tank 48. The side of the bellows on the outside of the tank assumes a position that is responsive to variations of ~Q~ 3 pressure within the tank and there is a linka~e 50 from the outer side of the ~ank that has a dial ~2 that assumes a position related to the pressure. Dial 52 acts on a poteniometer 5A, the output of ;
which is fed to an input of the transmitter 10. The input has an analogue to digital conventer which converts the analogue electrical output from the potentiometer 54 to a digital output and stores it for transmission. The output of the pressure sensing device is transmitted during the third eight bit piece of the ~0 minute word of each transmitter. Potentiometer 54 is powered from the battery source of the transmitter but only during transmission period.
Pressure sensing devices and potentiometers are well known in the art and further detail is not thought necessary.
Level within the tank is det~rmined by sensor 24. ~his is achieved by float 56 connected by means o~ a tape to a take-up rell that is spring loaded and located in the housi~g of the device 60. The shaft from the reel adopts a position related to the level of the ~oat. Shaft encoders are well known in the art and further detail of the mechanical features of a shaft encoder are not thought necessary. The mechanical output o~ the shaft of the shaft encoder is applied to an electrical circuit that produces a digital output and which is transmitted during the last sixteen bit interval of each forty bit word of each transmitter. Power for the circuit is obtained from the power source of the transmitter~ ' The arrangement of the bits in a transmitted word is capable of great variation and does not form an essential part of the invention. However, as indicated, in the forty bit word trans-mitted from each of the teansmitters 10 with this invention, the first eight bits transmitthe location or address of the transmitter and identify the link. The second eight bits transmits the output of the temperature sensing device. The th~d eight bits transmit the instant output of the pressure sensing device and ~he last sixteen `~
bits transmits the instant output o~ the level sensing device.
~ ~i33~3 ~:
Figure 6 is a view of the lower portion of an oil storage tank showing an installation according to this invention. Numeral 24 refers to the shaft encoder which detects level. Numeral 22 refers to the pressure sensing device and numeral 20 refers to the temperature sensing device. l~hey are all connected to the trans~
mitter 10 which, as indicated, is housed within an explosion pxoof ho~ing~ The compactness of the installation is apparent from Fiyure 6.
In the system, all clocks are reset to real time zero by the reset pulse originating from the charging source and clock drift is only significant on a "per scan" basis.
The invention has been effectively used on an oil tank f~rm having about 14 oil storage tanks each fitted with a transmitter like the transmitter 10 with sensors for level, pressure and temperature as described and adapted to send a word having the composition described to a receiver at a remote central location.
The bit rate for transmission was 50~ bits per second. All trans-sistors had crystal clocks of standard design and there was no difficulty in achieving a .01~ stability. The words were trans-mitted at 24 bit intervals, as described above. The charging pulsewas 24 volts and had a duration of about 4 seconds.
~ 11 clocks were set to real time zero by the reset pulse originating from the receiver location so that clock drift was only significant on a per scan basis.
The pulses had a generated amplitude of about 7 volts, as described above. The signals received by the receiver were de-coded and fed through a computer of standard design to give a readout of pressure, temperature and level.
Each transmitter took a time period of 64 bits to transmit including the quiet periods at the beginning and end of its 40 bit word. Thus, the 14 transmitters took 896 bits to complete a sentence.
,~
The elapsed time for the 896 bi-ts was less than two seconds. A
recharging period of ~I seconds was used and -the total elapsed time fox transmission of all transmitters and recharging was rounded off at 6 seconds. The master timer was, therefore, set to connect and disconnect the recharging source at intervals o~ ~ seconds.
The ~xamples and quantities given are by way of example only and not to be construed in a restrictive way. ~he embodiments of the invention other than the ones illustrated will be apparent ~ .
to those skilled in the art. .:
1 () , '' "
` ,'.
.
' .. . j ~
... . .
~ .
, . ,
Claims (6)
1. In an electrical data transmitting system, a plurality of transmitters each having a rechargeable power source, each having at least one sensor with its output connected to the input of its respective transmitter and each having a transmitter timer;
a data transmission line;
a receiver to receive signals transmitted over said data transmission line;
a master timer;
a recharging voltage source connectable to said transmission line to simultaneously recharge the rechargeable power source of each of said transmitters;
said transmitters being normally not connected to the transmission line for transmission; means for simulteneously setting the transmitter timer of each of said transmitters to connect its respective transmitter to the data transmission line whereby the plurality of transmitters are connected one at a time and in pre-determined time sequence to the data transmission line for trans-mission;
said transmitters when connected for transmission to said transmission line each being adapted to transmit information about their location and the output of their respective sensors to said receiver;
said master timer being cyclically operable to dictate connection of said recharging voltage source to said transmission line for a predetermined time to recharge the rechargeable power source as aforesaid, in a time interval following sequential data transmission by said plurality of transmitters as aforesaid;
said means for simultaneously setting said transmitter timers being responsive to operation of said master timer during said time interval following data transmission to set the trans-mitter timer of each of said transmitters as aforesaid.
a data transmission line;
a receiver to receive signals transmitted over said data transmission line;
a master timer;
a recharging voltage source connectable to said transmission line to simultaneously recharge the rechargeable power source of each of said transmitters;
said transmitters being normally not connected to the transmission line for transmission; means for simulteneously setting the transmitter timer of each of said transmitters to connect its respective transmitter to the data transmission line whereby the plurality of transmitters are connected one at a time and in pre-determined time sequence to the data transmission line for trans-mission;
said transmitters when connected for transmission to said transmission line each being adapted to transmit information about their location and the output of their respective sensors to said receiver;
said master timer being cyclically operable to dictate connection of said recharging voltage source to said transmission line for a predetermined time to recharge the rechargeable power source as aforesaid, in a time interval following sequential data transmission by said plurality of transmitters as aforesaid;
said means for simultaneously setting said transmitter timers being responsive to operation of said master timer during said time interval following data transmission to set the trans-mitter timer of each of said transmitters as aforesaid.
2. An electrical data transmitting system as claimed in Claim 1 in which each of said transmitters has more than one sensor.
3. An electrical data transmitting system as claimed in Claim 1 in which said sensor of said transmitter is electrically powered from the power source of its transmitter.
4. An electrical data transmitting system as claimed in Claim 1 in which said sensor of said transmitter is electrical-ly powered from the power source of its transmitter, said sensor being intermittently powered under control of the transmitter timer of its respective transmitter to provide a signal for trans-mission of its respective transmitter.
5. An electrical data transmitting system as claimed in Claim 1 in which said sensor of said transmitter is electrical-ly powered from the power source of its transmitter each of said transmitters having more than one sensor.
6. An electrical data transmitting system as claimed in Claim 1 in which said sensor of said transmitter is electrical-ly powered from the power source of its transmitter each of said transmitters having more than one sensor, said sensors being intermittently powered under control of the transmitter timer of their respective transmitter to provide a signal for transmission of its respective transmitter.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA248,270A CA1053343A (en) | 1976-03-19 | 1976-03-19 | Electrical data collecting device |
| GB1366376A GB1507609A (en) | 1976-03-19 | 1976-04-05 | Electrical data collecting device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA248,270A CA1053343A (en) | 1976-03-19 | 1976-03-19 | Electrical data collecting device |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1053343A true CA1053343A (en) | 1979-04-24 |
Family
ID=4105496
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA248,270A Expired CA1053343A (en) | 1976-03-19 | 1976-03-19 | Electrical data collecting device |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1053343A (en) |
| GB (1) | GB1507609A (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3004981C2 (en) * | 1980-02-11 | 1981-10-29 | Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt | Method for data transmission in great water depths |
| EP0055688A1 (en) * | 1980-12-23 | 1982-07-07 | Siemens Aktiengesellschaft | Signal transmission arrangement according to the time multiplex system |
| FR2623316B1 (en) * | 1987-11-17 | 1990-03-30 | Laborderie Alain | TIME-SHARING REMOTE CONTROL AND REMOTE MONITORING SYSTEM |
| US5122970A (en) * | 1988-06-17 | 1992-06-16 | Hewlett-Packard Company | Improved sensor |
| DE4325674A1 (en) * | 1993-07-30 | 1995-02-02 | Ruhrgas Ag | Method and arrangement for recording measured values and monitoring a product pipeline |
| EP0870176B1 (en) * | 1995-12-22 | 2003-03-19 | Brüel & Kjaer Sound & Vibration Measurement A/S | A system and a method for measuring a continuous signal |
| DE19647668A1 (en) | 1996-11-19 | 1998-05-28 | Bosch Gmbh Robert | Slave station, master station, BUS system and method for operating a BUS system |
-
1976
- 1976-03-19 CA CA248,270A patent/CA1053343A/en not_active Expired
- 1976-04-05 GB GB1366376A patent/GB1507609A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| GB1507609A (en) | 1978-04-19 |
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