CA1070410A - Sensing circuit - Google Patents
Sensing circuitInfo
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- CA1070410A CA1070410A CA274,059A CA274059A CA1070410A CA 1070410 A CA1070410 A CA 1070410A CA 274059 A CA274059 A CA 274059A CA 1070410 A CA1070410 A CA 1070410A
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- Canada
- Prior art keywords
- contact pair
- output
- circuitry
- pulses
- galvanic isolator
- Prior art date
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Abstract
ABSTRACT
A circuit for sensing closed and open states of an electrical contact pair in a monitoring station. The circuit includes a pulse generator for generating sampling pulses, a galvanic isolator, and an energy storage circuitry and the contact pair in series for allowing the pulse generator to apply the sampling pulses to the storage circuit via the galvanic isolator. The storage circuit stores enough charges to build a DC voltage of a certain magnitude using the sampling pulses, when the contact pair is open, and discharges the stored charge through the contact pair to the ground and allows the sampling pulses to go to the ground via the galvanic isolator and the storage circuitry, when the contact pair is and remains closed. The sensing circuit also includes an output circuitry coupled to the galvanic isolator for sensing the pulses being transmitted through the isolator and providing an output signal indicative of the open or closed state of the contact pair.
A circuit for sensing closed and open states of an electrical contact pair in a monitoring station. The circuit includes a pulse generator for generating sampling pulses, a galvanic isolator, and an energy storage circuitry and the contact pair in series for allowing the pulse generator to apply the sampling pulses to the storage circuit via the galvanic isolator. The storage circuit stores enough charges to build a DC voltage of a certain magnitude using the sampling pulses, when the contact pair is open, and discharges the stored charge through the contact pair to the ground and allows the sampling pulses to go to the ground via the galvanic isolator and the storage circuitry, when the contact pair is and remains closed. The sensing circuit also includes an output circuitry coupled to the galvanic isolator for sensing the pulses being transmitted through the isolator and providing an output signal indicative of the open or closed state of the contact pair.
Description
CM-76798 1~410 This invention relates to a sensing circuit and, more particularly, to an improved sensing circuit for sensing the status of a contact pair in a monitoring station.
BACKGROUND OF THE INVENTION
In a telemetry supervisory system which includes remote monitoring stations, it is customary to have a number of remote unmanned monitoring stations connected in a network with a master station. Each of such remote monitoring stations ususally has a number of remote points which it monitors and whose status it reports to the master station.
These remote points are often monitored by a pair of con-tacts, which are connected by a wire-pair of substantial length.
A prior art system such as that described hereinabove, suffers from a number of shortcomings and problems. Thus, for example, the prior system is noise sensitive in that noise induced in the long wires between the remote points and the remote monitoring stations tend to induce errors in the status indications which are reported. The prior art system is also susceptible to transient surges induced on the long wires or yenerated by the opening and the closing of the remote contacts which tend to damage the equipment at the reporting station. Moreover, the prior art system is not very e~ficient in the power consumption in that in the event of power failure battery operation is usually necessary until the power is restored by using an auxiliary battery provided on a standby basis.
According to the prior art, the noise problem is over-come by having a galvanic isolation circuitry interposed between the wires from the remote points and the reporting
BACKGROUND OF THE INVENTION
In a telemetry supervisory system which includes remote monitoring stations, it is customary to have a number of remote unmanned monitoring stations connected in a network with a master station. Each of such remote monitoring stations ususally has a number of remote points which it monitors and whose status it reports to the master station.
These remote points are often monitored by a pair of con-tacts, which are connected by a wire-pair of substantial length.
A prior art system such as that described hereinabove, suffers from a number of shortcomings and problems. Thus, for example, the prior system is noise sensitive in that noise induced in the long wires between the remote points and the remote monitoring stations tend to induce errors in the status indications which are reported. The prior art system is also susceptible to transient surges induced on the long wires or yenerated by the opening and the closing of the remote contacts which tend to damage the equipment at the reporting station. Moreover, the prior art system is not very e~ficient in the power consumption in that in the event of power failure battery operation is usually necessary until the power is restored by using an auxiliary battery provided on a standby basis.
According to the prior art, the noise problem is over-come by having a galvanic isolation circuitry interposed between the wires from the remote points and the reporting
- 2 -CM-76798 1~410 station equipment. To resolve the transient surge problems, the prior art system uses filters and clippers or any equiva-lent limiters in addition to the galvanic isolator to reduce the magnitude of the surges.
These prior art solutions to the foregoing problems generally require a large increase in the current drain of the xeporting station and consequently reduces the overall power efficiency of the station and of the system.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved sensing circuitry.
It is still another object of the present invention to provide an improved sensing circuitry in a station being monitored that overcomes one or more of the aforementioned shortcomings and problems.
It is yet another object of the present invention to provide a solution to the aforementioned proble~.s with no or minimum level of incxease in the current drain required to operate the monitoring station.
The foregoing and other objects of the present invention are attained by providing a pulse generator for generating sampling pulses, and an energy storage circuitry coupled to the contact pair and to the pulse generator through a gal-vanic isolator and an output circuitry coupled to the galvanic isolator for pro~iding an output signal indicative of the status, i.e., open or closed state, of the contact pair.
According to a feature o~ the present invention, the energy storage circuitry is used to store the sampling pulses until the storage circuit stores enough charges to build a DC voltage o a certain magnitude using the sampling C~1-76798 l~V410 pulses when the contact pair is in the open state. When the contact pair i5 closed, the storage circuit is allowed to discharge the stored charge through the contac~ pair to the ground and the pulse generator is allowed to apply the sampling pulses to the ground v~a the galvanic isolator and the storage circuitry.
According to another feature of the present invention, the output circuitry is provided with a flip-flop circuitry for amplifying and widening the output of the galvanic isolator, a low pass filter for eliminating short negative pulses and transients from the output of the flip-flop circuitry to prevent change in the state of its output signal while the energy storage circuitry is being charged and remains charged and allows change in the state of its output signal upon discharge of the energy storage circuitry while the sample pulses are being transmitted through the isolator to the ground, when the contact pair is closed, and a binary gate responsive to the output of the filter for providing the output signal signifying the change in the state of the contact.
The foregoing and other objects and features of the present invention will b~come clear from the following detailed description of an illustrative embodiment of the present invention in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure l illustrates a prior art sensing circuitry in a functional block diagram.
Figure 2 illustrates an illustrative embodiment of a sensing circuitr~ in a functional block diagram in accordance with the present invention.
CM-76798 ~07~410 Figure 3 illustrates a sampling pulse generator circuit that may be used in a present sensing circuitry.
Figure 4 illustrates an input isolation/surge protection circuit employing the sampling technique in accordance with the present invention.
Figure 5 shows timing diagram that illustrates the operation of the sensing circuit.
DETAILED DESCRIPTION
Figure 1 illustrates a commonly used prior art sensing circuit 1 which provides galvanic isolation and surge protec-tion but which requires high current drain. The prior artsensing circuitry includes a DC to DC converter 2 for provid-ing an isolated constant DC voltage of a suitable voltage from a DC power supply to each of a plurality of galvanic isolators 3 used for a plurality of monitoring stations in a supervisory telemetry system. T~pically, the supervisory telemetry system includes a plurality of sensing circuitry such as that shown in Fig. 1 for monitoring a plurality of corresponding remotely located contact pairs. For the sake of simplicity only one sensing circuitry and one remote contact pair is shown in Fig. 1.
The galvanic isolator 3 may be of any suitable conven-tional circuitry such as a relay or an optical isolator or a transformer. When a remote contact pair 5 is closed, DC
current flows from the DC to DC converter 1, via the control section 3A of the galvanic isolator 3, a low pass filter and ~lipper 4 and the remote contact pair 5 to the remote ground 6. This current flow causes a corresponding state in the controlled section 3B of the galvanic isolator which is sensed and sent out to a reporting equipment 8. The low CM-76798 ~(~'7(3410 pass filter and clipper 4 filters noise and clips surge voltages originating at the remote contact pair 5 or on the connecting line. A low pass filter 9 is also interposed between the galvanic isolator and the reporting equipment to provide additional noise immunity. Usually, separate ground 7 is provided between the remote ground 6 and the equipment ground.
According to the prior art, the current level required by the controlling section 3A of the galvanic isolator for proper operation must be continuous when the remote contact pair is closed. In a typical supervisory telemetry system that monitors many pairs of the monitoring stations, this current is multiplied by the number of contact pairs which are closed at any given time. Hence, considerable amount of current drain is involved in a typical supervisory telemetry system that includes a large number of monitoring stations.
In accordance with the present invention, the afore-mentioned shortcomings, including the large current drain, are overcome by a system based on a sampling technique.
Thus, by providing sampling pulses to the sensing circuitry for just a portion of monitoring time, in pulses, substantial energy is saved. The conventional galvanic isolator can be used also by using a suitable output circuitry that includes means of stretching and/or smoothing the pulse output. The sampling technique is used to provide appropriate output signal indicative of the status of the contact pair being monitored.
The principle of this invention, namely, the utilization of the sampling technique is implemented by a sensing circuitry 10 illustrated in Fig. 2. Thus, referring to Fig. 2, there is shown, in a functional block diagram form, a sensing CM-7679g 107~'~10 circuitry which utilizes a sampling pulse train, instead of a steady DC voltage, as used in the prior art sensing circuitry illustrated in Fig. 1. As shown in Fig. 2, the inventive sensing circuitry includes a sampling pulse generator 11 which may provide the same peak DC voltage as that of the prior art DC to DC converter shown in Fig. 1. The low pass filter and clipper 4 coupled to the remote contact pair 5 and the galvanic isolator 3 may be of the same type as those used in the prior art sensing circuitry shown in Fig. 1.
Likewise, a low pass filter 4 of the type used in the prior art sensing circuitry in the output may also be used in the sensing circuit of the present invention.
Usually, all of the remote contact pairs 5 in a telemetry supervisory system, are held open under a normal condition.
This permits the sampling pulses to pass through the control section 3A of the galvanic isolator 3 into the energy storage circuit 13 of a suitable design, such as DC storage circuit of a conventional design. When a sufficient number of pulses enter and charge the energy storage circuit 13 up to a level equal to the peak voltage of the sampling pulse, the sampling pulses cease to flow through the control section of the galvanic isolator 3, and the energy storage circuit remains charged and this is the case as long as the remote contact pair 5 is open. A low pass filter g coupled to the galvanic isolator output via a flip-flop 15, has a time constant which is long enough to prevent switching of the binary gate 10 during the charging of the energy storage unit 13. This pre~ents the entry of an apparent change of state signal to the reporting equipment 8 during the charging of the energy storage circuit 13~
Once the energy storage circuit 13 has been loaded, the circuit of Figure 2, is ready to respond to closure of the ~ 07~)4~0 ~M-76798 remote contact pair 5. When the remote contact pair 5 is closed, as it would when a suitable circuitry such as a relay (not shown) controlling the pair is actuated to signify a change of a condition, it effectively shunts the energy storage circuit 13. The charge stored in the storage circuit is then discharged, in the form of a DC current, to the ground 6 via remote relay contacts 5 and low pass filter and clipper 4. Once the charge in the energy storage circuit 13 is discharged, the sampling pulses are allowed to flow to the ground through the controlling section 3A of the galvanic isolator, the energy storage circuit, and the contact pair.
The flow of sampling pulses through the controlling section 3A of the galvanic isolator 3 induces a corresponding pulse train to appear at the output of the controlled section 3B.
If the pulses appearing in the controlled section 3B of the galvanic isolator 3 are narrow, it is necessary to amplify and/or widen them, before they are averaged. The most economical way of achieving this is with a flip-flop 15. As shown, such a flip-flop can be interposed between the galvanic isol~tor 3 and the low pass filter 9. Pulses from the reset pulse signal source 12, which drives the sampling pulse generator 11, can also be used as reset pulses to the flip-~lop 15. The reset pulses are set to occur just prior to the occurence of the sampling pulses.
~eset pulses drive the flip-flop 15 output high, and the output pulses of the isolator 3 then drive the output low.
Consequently, the flip-flop output will be maintained at the positive supply voltage of the ~lip-~lop continuously, while the contact pair is open. When the contact pair is closed, the sampling pulses induce output pulses in the galvanic isolator output. The output of the isolator and the reset CM-76798 1~410 pulses causes the flip-flop to change its output from a high DC value into a train of pulses. The output of the flip-flop 15 is then filtered by the low pass filter g to eliminate the short negative pulse and other transients. The low pass filter 9 is also designed to prevent a change-of-state signal during the charging and discharging of the energy storage circuit 13. This prevents the sensing circuit from sending out a false output signal caused by noise or transients.
Following a period of time delay after the closing of the contact pair, the output voltage of the low pass filter 9 reaches the switching threshold voltage of a binary gate 14 and causes it to switch. This generates a change of state signal and this signifies a contact closure, which is then processed by the reporting equipment 8.
The low pass filter and clipper 4 serves the same function as that of the prior art as shown in Figure 1. The isolation between the input and output of the galvanic isolator is improved substantially by the use of separate grounds 6 and 7 as illustrated in Figure 2. This provides improved surge protection function.
Figures 3 and 4 illustrate, respectively, specific cir-cuitry used for generating the sampling pulses and providing an isolation/surge protection to the sensing circuit in accordance with the present invention.
Referring to Figure 3, the sampling pulse generator circuit includes three conventional complementary emitter-follower transistor pairs, Ql and Q2, Q3 and Q4, and Q5 and Q6 coupled in series, a transformer Tl that is interposed between the first two emitter-transistor pairs and that provides a galvanic isolation between the input and output terminals, 31 and 32. Three emitter-follower transistor pairs, transformer Tl and a passive circuit network are g _ 1~)7V410 designed to elements provide a sampling pulse at the output 35, which is slightiy time delayed with respect to the reset pulses applied at the input thereof from reset pulse source 12. The passive circuit network includes capacitor C7 and diodes CRl, CR2, which are operatively coupled to the trans-former as illustrated to generate a ringing waveform when the reset pulse is finished. By virtue of the polarity inversion achieved by Tl, the first pulse of the ringing waveform is positive. This pulse is the sampling pulse and is present at the end of the reset pulse.
Figure 4 shows an illustrative detail of circuit elements that provide isolation/surge prevention function for the galvanic isolator 3, flip-flop 15, and low pass filter 9 of the output circuitry. The galvanic isolator may be in the form a a transformer Tll. The energy storage circuit is a peak detector, consisting o~ diode CR3 and capacitor Cll. Cll is also a part of the low pass filter and clipper, which also includes resistor Rll, and diodes CRll and CR12. The inductance of Tll, together with the capacitor C12, generate a ringing waYeform, in the same way as the sampling pulse generator does as described above.
The first pulse of the ringing drives the flip-flop which consists of two NOR gates Gll and G12. The low pass filter is composed of resistor RlZ and capacitor C13.
Binary gate G13 then provides the change of state signal in the form required for the reporting equipment.
For each remote contact pair, a circuit such as the one shown in Figure 4 is required, but only a single sampling pulse generator is required for a complete set of remote stations being monitored.
The overall operation of the present sensing circuit shown in Figures Z, 3, and 4 will now be explained with C.~-7679~ 107V410 reference to the timing diagram waveforms shown in Figure 5.
The reset pulse source 12 provides a train of reset pulses as shown in the waveform A in Figure 5. The sampling puise generator responds to the reset pulses and generates a train of sampling pulses as shown in waveform B in Figure 5. Note that the sampling pulses are essentially the same as those of the reset pulses except for the time delay introduced by the sampling pulse generator. While the contact pair 5 is open, the storage output of the storage circuit 13 remains high as illustrated in waveform C in Figure 5. While the contact pair 5 is open, there is no output in the output of the galvanic isolator 3 as shown in waveform E in Figure 5.
The output of the flip-flop 15 and the low pass filter 9 remains high and the output of the binary gate 14 remains low as illustrated in the waveforms F, G, and H respectively in Figure 5 while the contact pair 5 remains open.
Assume at time tl the contact pair closes and thereafter remains closed. The sampling pulse generator continues to apply the sampling pulses in response to the reset pulses as shown in waveform B of Figure 5. However, the storage circuit 13 begins to dischar~e at time tl and this continues until time t2. The stored charge is discharged through the contact pair gradually by the action of the low pass filter and clipper as illustrated in waveform C in Figure 5. This continues until the charge stored at the capacitor 11 is completely discharged by the time t2. As the capacitor discharges the transformer Tll begines to induce a train of output pulses in the output pulses in its output windings of the transformer Tll. The pulse amplitude of the output of the galvanic isolator at capacitor C12 begins to increase until it reaches the amplitude corresponding to that of the input sampling pulses and this takes place during the transition CM-76798 1(~7~'~10 ~etween time tl and time t2 while the charge stored in the storage 13 is drained. Thereafter the output of the galvanic isolator provides a train of pulses in response to the train of pulses applied to the galvanic isolator by the sampling pulse generator. The output pulse train of the galvanic isolator is the same as the input pulse train in the form of the sampling pulses except for a time delay introduced by the output windings of the transformer and the capacitor C12. The reset pulses (Fig. 5; A) are applied to the gate G12 of the flip-flop 15 and the output pulses (Fig. 5; E) of the galvanic isolator are applied to the other gate Gll of the flip-flop. These two pulse trains cause the flip-flop 15 to flip-flop its output between a low and high voltage.
Referring to ~ig. 5, waveforms A, E and F, it is evident that until the amplitude of the output pulses of the galvanic isolator reaches a certain level, the gate Gll does not cause the flip-flop output to change. Only when the voltage amplitude of the isolator is high enough does the flip-flop change its output voltage~ Once the output amplitude is high enough, then as noted, the reset pulse causes the flip-flop output to go high and the pulse from the isolator causes the output to go low. In this manner, the flip-flop 15 begins to provide a train of pulses toward the end of the time t2 when the storage 13 is discharged. Thereafter, the output of the flip-flop tracks the pulse train output of the galvanic isolator and the reset pulse train.
The output of the flip-flop is applied to the low pass filter 9 made of RC circuit R12 and C13. As the output of the flip-flop changes from DC to AC pulse train, the capacitor C13 begins to discharge and consequently the voltage output at the low pass filter 9 begins to decrease as the output of the flip-flop applied to the low pass filter begins to 107(~410 change from DC to AC pulse train. The pulse train of the flip-flop continues to cause the capacitor C13 to discharge to a certain potential where the potential causes the binary gate G13 to change its output from a low to a high level output at time t3. Change of the output of the binary gate signifies the fact that the contact pair 5 is now closed.
Now, when the contact pair 5 again opens up, the process will be reversed and the storage 13 will begin to charge and thus its output will climb hack to a DC voltage as shown at the beginning of the time waveform C in Figure S. This will cause the output of the galvanic isolator in the form of pulse train to decrease and eventually dis-appear as the storage circuit capacitor C11 charges to a potential enough to prevent transformer Tll from inducing any output voltage in the galvanic isolator. In turn this will prevent the galvanic isolator from generating pulse train output and this will ir, turn cause the output of the flip-flop to stop generating a pulse train and have its output go high. In turn, this will cause the output of the low pass filter go high and the output of the binary gate 14 go low thereby indicating the open state of the contact pair.
The time delay introduced between the opening and closing of the contact pair 5 and actual sensing of the change is by design and deliberate. This is to prevent any tran-sient pulses or noise signals that are likely present in the sensing circuit from falsely inducing changes in the output of the binary gate 14. Usually the transient or noise is of a short duration. The interference by the noise or transient signal is eliminated by the use of the low pass filters 4 and 9 and flip-flop 15. However, the 107()410 filters and flip-flop cause the time delay between the time the change in the state of the contact pair and the sensing of the change in the output of the binary gate 14.
But, this delay is of no significance and does not adversely affect the end result in that usually the time delay is not critical in applications.
In summary, then, in accordance with the present invention, there is shown an illustrative embodiment that is based on a sampling technique for improving a sensing circuitry that overcomes various shortcomings and diffi-culties of the prior art sensing circuitry and that provides better noise isolation and surge current prevention and that improves power efficiency by reducing the energy required by the sensing circuitry.
~ 14 -
These prior art solutions to the foregoing problems generally require a large increase in the current drain of the xeporting station and consequently reduces the overall power efficiency of the station and of the system.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved sensing circuitry.
It is still another object of the present invention to provide an improved sensing circuitry in a station being monitored that overcomes one or more of the aforementioned shortcomings and problems.
It is yet another object of the present invention to provide a solution to the aforementioned proble~.s with no or minimum level of incxease in the current drain required to operate the monitoring station.
The foregoing and other objects of the present invention are attained by providing a pulse generator for generating sampling pulses, and an energy storage circuitry coupled to the contact pair and to the pulse generator through a gal-vanic isolator and an output circuitry coupled to the galvanic isolator for pro~iding an output signal indicative of the status, i.e., open or closed state, of the contact pair.
According to a feature o~ the present invention, the energy storage circuitry is used to store the sampling pulses until the storage circuit stores enough charges to build a DC voltage o a certain magnitude using the sampling C~1-76798 l~V410 pulses when the contact pair is in the open state. When the contact pair i5 closed, the storage circuit is allowed to discharge the stored charge through the contac~ pair to the ground and the pulse generator is allowed to apply the sampling pulses to the ground v~a the galvanic isolator and the storage circuitry.
According to another feature of the present invention, the output circuitry is provided with a flip-flop circuitry for amplifying and widening the output of the galvanic isolator, a low pass filter for eliminating short negative pulses and transients from the output of the flip-flop circuitry to prevent change in the state of its output signal while the energy storage circuitry is being charged and remains charged and allows change in the state of its output signal upon discharge of the energy storage circuitry while the sample pulses are being transmitted through the isolator to the ground, when the contact pair is closed, and a binary gate responsive to the output of the filter for providing the output signal signifying the change in the state of the contact.
The foregoing and other objects and features of the present invention will b~come clear from the following detailed description of an illustrative embodiment of the present invention in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure l illustrates a prior art sensing circuitry in a functional block diagram.
Figure 2 illustrates an illustrative embodiment of a sensing circuitr~ in a functional block diagram in accordance with the present invention.
CM-76798 ~07~410 Figure 3 illustrates a sampling pulse generator circuit that may be used in a present sensing circuitry.
Figure 4 illustrates an input isolation/surge protection circuit employing the sampling technique in accordance with the present invention.
Figure 5 shows timing diagram that illustrates the operation of the sensing circuit.
DETAILED DESCRIPTION
Figure 1 illustrates a commonly used prior art sensing circuit 1 which provides galvanic isolation and surge protec-tion but which requires high current drain. The prior artsensing circuitry includes a DC to DC converter 2 for provid-ing an isolated constant DC voltage of a suitable voltage from a DC power supply to each of a plurality of galvanic isolators 3 used for a plurality of monitoring stations in a supervisory telemetry system. T~pically, the supervisory telemetry system includes a plurality of sensing circuitry such as that shown in Fig. 1 for monitoring a plurality of corresponding remotely located contact pairs. For the sake of simplicity only one sensing circuitry and one remote contact pair is shown in Fig. 1.
The galvanic isolator 3 may be of any suitable conven-tional circuitry such as a relay or an optical isolator or a transformer. When a remote contact pair 5 is closed, DC
current flows from the DC to DC converter 1, via the control section 3A of the galvanic isolator 3, a low pass filter and ~lipper 4 and the remote contact pair 5 to the remote ground 6. This current flow causes a corresponding state in the controlled section 3B of the galvanic isolator which is sensed and sent out to a reporting equipment 8. The low CM-76798 ~(~'7(3410 pass filter and clipper 4 filters noise and clips surge voltages originating at the remote contact pair 5 or on the connecting line. A low pass filter 9 is also interposed between the galvanic isolator and the reporting equipment to provide additional noise immunity. Usually, separate ground 7 is provided between the remote ground 6 and the equipment ground.
According to the prior art, the current level required by the controlling section 3A of the galvanic isolator for proper operation must be continuous when the remote contact pair is closed. In a typical supervisory telemetry system that monitors many pairs of the monitoring stations, this current is multiplied by the number of contact pairs which are closed at any given time. Hence, considerable amount of current drain is involved in a typical supervisory telemetry system that includes a large number of monitoring stations.
In accordance with the present invention, the afore-mentioned shortcomings, including the large current drain, are overcome by a system based on a sampling technique.
Thus, by providing sampling pulses to the sensing circuitry for just a portion of monitoring time, in pulses, substantial energy is saved. The conventional galvanic isolator can be used also by using a suitable output circuitry that includes means of stretching and/or smoothing the pulse output. The sampling technique is used to provide appropriate output signal indicative of the status of the contact pair being monitored.
The principle of this invention, namely, the utilization of the sampling technique is implemented by a sensing circuitry 10 illustrated in Fig. 2. Thus, referring to Fig. 2, there is shown, in a functional block diagram form, a sensing CM-7679g 107~'~10 circuitry which utilizes a sampling pulse train, instead of a steady DC voltage, as used in the prior art sensing circuitry illustrated in Fig. 1. As shown in Fig. 2, the inventive sensing circuitry includes a sampling pulse generator 11 which may provide the same peak DC voltage as that of the prior art DC to DC converter shown in Fig. 1. The low pass filter and clipper 4 coupled to the remote contact pair 5 and the galvanic isolator 3 may be of the same type as those used in the prior art sensing circuitry shown in Fig. 1.
Likewise, a low pass filter 4 of the type used in the prior art sensing circuitry in the output may also be used in the sensing circuit of the present invention.
Usually, all of the remote contact pairs 5 in a telemetry supervisory system, are held open under a normal condition.
This permits the sampling pulses to pass through the control section 3A of the galvanic isolator 3 into the energy storage circuit 13 of a suitable design, such as DC storage circuit of a conventional design. When a sufficient number of pulses enter and charge the energy storage circuit 13 up to a level equal to the peak voltage of the sampling pulse, the sampling pulses cease to flow through the control section of the galvanic isolator 3, and the energy storage circuit remains charged and this is the case as long as the remote contact pair 5 is open. A low pass filter g coupled to the galvanic isolator output via a flip-flop 15, has a time constant which is long enough to prevent switching of the binary gate 10 during the charging of the energy storage unit 13. This pre~ents the entry of an apparent change of state signal to the reporting equipment 8 during the charging of the energy storage circuit 13~
Once the energy storage circuit 13 has been loaded, the circuit of Figure 2, is ready to respond to closure of the ~ 07~)4~0 ~M-76798 remote contact pair 5. When the remote contact pair 5 is closed, as it would when a suitable circuitry such as a relay (not shown) controlling the pair is actuated to signify a change of a condition, it effectively shunts the energy storage circuit 13. The charge stored in the storage circuit is then discharged, in the form of a DC current, to the ground 6 via remote relay contacts 5 and low pass filter and clipper 4. Once the charge in the energy storage circuit 13 is discharged, the sampling pulses are allowed to flow to the ground through the controlling section 3A of the galvanic isolator, the energy storage circuit, and the contact pair.
The flow of sampling pulses through the controlling section 3A of the galvanic isolator 3 induces a corresponding pulse train to appear at the output of the controlled section 3B.
If the pulses appearing in the controlled section 3B of the galvanic isolator 3 are narrow, it is necessary to amplify and/or widen them, before they are averaged. The most economical way of achieving this is with a flip-flop 15. As shown, such a flip-flop can be interposed between the galvanic isol~tor 3 and the low pass filter 9. Pulses from the reset pulse signal source 12, which drives the sampling pulse generator 11, can also be used as reset pulses to the flip-~lop 15. The reset pulses are set to occur just prior to the occurence of the sampling pulses.
~eset pulses drive the flip-flop 15 output high, and the output pulses of the isolator 3 then drive the output low.
Consequently, the flip-flop output will be maintained at the positive supply voltage of the ~lip-~lop continuously, while the contact pair is open. When the contact pair is closed, the sampling pulses induce output pulses in the galvanic isolator output. The output of the isolator and the reset CM-76798 1~410 pulses causes the flip-flop to change its output from a high DC value into a train of pulses. The output of the flip-flop 15 is then filtered by the low pass filter g to eliminate the short negative pulse and other transients. The low pass filter 9 is also designed to prevent a change-of-state signal during the charging and discharging of the energy storage circuit 13. This prevents the sensing circuit from sending out a false output signal caused by noise or transients.
Following a period of time delay after the closing of the contact pair, the output voltage of the low pass filter 9 reaches the switching threshold voltage of a binary gate 14 and causes it to switch. This generates a change of state signal and this signifies a contact closure, which is then processed by the reporting equipment 8.
The low pass filter and clipper 4 serves the same function as that of the prior art as shown in Figure 1. The isolation between the input and output of the galvanic isolator is improved substantially by the use of separate grounds 6 and 7 as illustrated in Figure 2. This provides improved surge protection function.
Figures 3 and 4 illustrate, respectively, specific cir-cuitry used for generating the sampling pulses and providing an isolation/surge protection to the sensing circuit in accordance with the present invention.
Referring to Figure 3, the sampling pulse generator circuit includes three conventional complementary emitter-follower transistor pairs, Ql and Q2, Q3 and Q4, and Q5 and Q6 coupled in series, a transformer Tl that is interposed between the first two emitter-transistor pairs and that provides a galvanic isolation between the input and output terminals, 31 and 32. Three emitter-follower transistor pairs, transformer Tl and a passive circuit network are g _ 1~)7V410 designed to elements provide a sampling pulse at the output 35, which is slightiy time delayed with respect to the reset pulses applied at the input thereof from reset pulse source 12. The passive circuit network includes capacitor C7 and diodes CRl, CR2, which are operatively coupled to the trans-former as illustrated to generate a ringing waveform when the reset pulse is finished. By virtue of the polarity inversion achieved by Tl, the first pulse of the ringing waveform is positive. This pulse is the sampling pulse and is present at the end of the reset pulse.
Figure 4 shows an illustrative detail of circuit elements that provide isolation/surge prevention function for the galvanic isolator 3, flip-flop 15, and low pass filter 9 of the output circuitry. The galvanic isolator may be in the form a a transformer Tll. The energy storage circuit is a peak detector, consisting o~ diode CR3 and capacitor Cll. Cll is also a part of the low pass filter and clipper, which also includes resistor Rll, and diodes CRll and CR12. The inductance of Tll, together with the capacitor C12, generate a ringing waYeform, in the same way as the sampling pulse generator does as described above.
The first pulse of the ringing drives the flip-flop which consists of two NOR gates Gll and G12. The low pass filter is composed of resistor RlZ and capacitor C13.
Binary gate G13 then provides the change of state signal in the form required for the reporting equipment.
For each remote contact pair, a circuit such as the one shown in Figure 4 is required, but only a single sampling pulse generator is required for a complete set of remote stations being monitored.
The overall operation of the present sensing circuit shown in Figures Z, 3, and 4 will now be explained with C.~-7679~ 107V410 reference to the timing diagram waveforms shown in Figure 5.
The reset pulse source 12 provides a train of reset pulses as shown in the waveform A in Figure 5. The sampling puise generator responds to the reset pulses and generates a train of sampling pulses as shown in waveform B in Figure 5. Note that the sampling pulses are essentially the same as those of the reset pulses except for the time delay introduced by the sampling pulse generator. While the contact pair 5 is open, the storage output of the storage circuit 13 remains high as illustrated in waveform C in Figure 5. While the contact pair 5 is open, there is no output in the output of the galvanic isolator 3 as shown in waveform E in Figure 5.
The output of the flip-flop 15 and the low pass filter 9 remains high and the output of the binary gate 14 remains low as illustrated in the waveforms F, G, and H respectively in Figure 5 while the contact pair 5 remains open.
Assume at time tl the contact pair closes and thereafter remains closed. The sampling pulse generator continues to apply the sampling pulses in response to the reset pulses as shown in waveform B of Figure 5. However, the storage circuit 13 begins to dischar~e at time tl and this continues until time t2. The stored charge is discharged through the contact pair gradually by the action of the low pass filter and clipper as illustrated in waveform C in Figure 5. This continues until the charge stored at the capacitor 11 is completely discharged by the time t2. As the capacitor discharges the transformer Tll begines to induce a train of output pulses in the output pulses in its output windings of the transformer Tll. The pulse amplitude of the output of the galvanic isolator at capacitor C12 begins to increase until it reaches the amplitude corresponding to that of the input sampling pulses and this takes place during the transition CM-76798 1(~7~'~10 ~etween time tl and time t2 while the charge stored in the storage 13 is drained. Thereafter the output of the galvanic isolator provides a train of pulses in response to the train of pulses applied to the galvanic isolator by the sampling pulse generator. The output pulse train of the galvanic isolator is the same as the input pulse train in the form of the sampling pulses except for a time delay introduced by the output windings of the transformer and the capacitor C12. The reset pulses (Fig. 5; A) are applied to the gate G12 of the flip-flop 15 and the output pulses (Fig. 5; E) of the galvanic isolator are applied to the other gate Gll of the flip-flop. These two pulse trains cause the flip-flop 15 to flip-flop its output between a low and high voltage.
Referring to ~ig. 5, waveforms A, E and F, it is evident that until the amplitude of the output pulses of the galvanic isolator reaches a certain level, the gate Gll does not cause the flip-flop output to change. Only when the voltage amplitude of the isolator is high enough does the flip-flop change its output voltage~ Once the output amplitude is high enough, then as noted, the reset pulse causes the flip-flop output to go high and the pulse from the isolator causes the output to go low. In this manner, the flip-flop 15 begins to provide a train of pulses toward the end of the time t2 when the storage 13 is discharged. Thereafter, the output of the flip-flop tracks the pulse train output of the galvanic isolator and the reset pulse train.
The output of the flip-flop is applied to the low pass filter 9 made of RC circuit R12 and C13. As the output of the flip-flop changes from DC to AC pulse train, the capacitor C13 begins to discharge and consequently the voltage output at the low pass filter 9 begins to decrease as the output of the flip-flop applied to the low pass filter begins to 107(~410 change from DC to AC pulse train. The pulse train of the flip-flop continues to cause the capacitor C13 to discharge to a certain potential where the potential causes the binary gate G13 to change its output from a low to a high level output at time t3. Change of the output of the binary gate signifies the fact that the contact pair 5 is now closed.
Now, when the contact pair 5 again opens up, the process will be reversed and the storage 13 will begin to charge and thus its output will climb hack to a DC voltage as shown at the beginning of the time waveform C in Figure S. This will cause the output of the galvanic isolator in the form of pulse train to decrease and eventually dis-appear as the storage circuit capacitor C11 charges to a potential enough to prevent transformer Tll from inducing any output voltage in the galvanic isolator. In turn this will prevent the galvanic isolator from generating pulse train output and this will ir, turn cause the output of the flip-flop to stop generating a pulse train and have its output go high. In turn, this will cause the output of the low pass filter go high and the output of the binary gate 14 go low thereby indicating the open state of the contact pair.
The time delay introduced between the opening and closing of the contact pair 5 and actual sensing of the change is by design and deliberate. This is to prevent any tran-sient pulses or noise signals that are likely present in the sensing circuit from falsely inducing changes in the output of the binary gate 14. Usually the transient or noise is of a short duration. The interference by the noise or transient signal is eliminated by the use of the low pass filters 4 and 9 and flip-flop 15. However, the 107()410 filters and flip-flop cause the time delay between the time the change in the state of the contact pair and the sensing of the change in the output of the binary gate 14.
But, this delay is of no significance and does not adversely affect the end result in that usually the time delay is not critical in applications.
In summary, then, in accordance with the present invention, there is shown an illustrative embodiment that is based on a sampling technique for improving a sensing circuitry that overcomes various shortcomings and diffi-culties of the prior art sensing circuitry and that provides better noise isolation and surge current prevention and that improves power efficiency by reducing the energy required by the sensing circuitry.
~ 14 -
Claims (7)
1. A circuit for sensing closed and open states of an electrical contact pair in a monitoring station, one end of the contact pair connectable to a ground, the circuit comprising:
a pulse generator for generating sampling pulses, a galvanic isolator, an energy storage circuitry coupled to the pulse generator through the galvanic isolator and coupled to the other end of the contact pair for allowing the pulse gener-ator to apply the sampling pulses to the storage circuit until the storage circuit stores enough charges to build a DC voltage of a certain magnitude using the sampling pulses when the contact pair is in the open state, the storage circuit discharging the stored charge through the contact pair to the ground and the pulse generator applying the sampling pulses to the ground via the galvanic isolator and the storage circuitry while the contact pair remains closed, and an output circuitry coupled to the galvanic iso-lator for sensing the pulses being transmitted through the isolator and providing an output signal indicative of change in the state of the contact pair from closed to open state and vice versa.
a pulse generator for generating sampling pulses, a galvanic isolator, an energy storage circuitry coupled to the pulse generator through the galvanic isolator and coupled to the other end of the contact pair for allowing the pulse gener-ator to apply the sampling pulses to the storage circuit until the storage circuit stores enough charges to build a DC voltage of a certain magnitude using the sampling pulses when the contact pair is in the open state, the storage circuit discharging the stored charge through the contact pair to the ground and the pulse generator applying the sampling pulses to the ground via the galvanic isolator and the storage circuitry while the contact pair remains closed, and an output circuitry coupled to the galvanic iso-lator for sensing the pulses being transmitted through the isolator and providing an output signal indicative of change in the state of the contact pair from closed to open state and vice versa.
2. The sensing circuit according to claim 1, including a circuitry interposed between the energy storage circuitry and the contact pair for filtering noise and clipping surge voltages originating at the contact or in the connecting line.
3. The sensing circuit according to claim 1, wherein the output circuitry includes:
a flip-flop circuitry for amplifying and widening the output of the galvanic isolator, a low pass filter for eliminating short negative pulse and transients from the output of the flip-flop circuitry to prevent change in the state of its output signal while the energy storage circuitry is being charged and remains charged and allow change in the state of its output signal upon discharge of the energy storage circuitry while the sample pulses are being transmitted to the ground through the galvanic isolator, when the contact pair is closed, and a binary gate responsive to the output of the filter for providing the output signal signifying the change of the state of the contact pair.
a flip-flop circuitry for amplifying and widening the output of the galvanic isolator, a low pass filter for eliminating short negative pulse and transients from the output of the flip-flop circuitry to prevent change in the state of its output signal while the energy storage circuitry is being charged and remains charged and allow change in the state of its output signal upon discharge of the energy storage circuitry while the sample pulses are being transmitted to the ground through the galvanic isolator, when the contact pair is closed, and a binary gate responsive to the output of the filter for providing the output signal signifying the change of the state of the contact pair.
4. The sensing circuit according to claim 3, including means for resetting the sampling pulse generator and the flip-flop circuitry.
5. The circuit according to claim 3, wherein the ground path of the output circuitry is isolated from the ground path coupled to the contact pair.
6. The sensing circuit according to claim 4, the pulse generator includes:
first series coupled complementary emitter-follower transistor pairs coupled to the means for resetting the sampling pulse generator, second series coupled comple-mentary emitter-follow transistor pairs;
a transformer interposed between the first and the second complementary emitter-follower pairs, a network of a capacitor, diodes and a resistor operately coupled to the transformer whereby the pulse generator is adapted to generate a ringing waveform as the sampling pulses; and third series coupled complementary emitter-follower transistor pairs interposed between the output of the second series coupled complementary emitter-follower transistor pair and the galvanic isolator.
first series coupled complementary emitter-follower transistor pairs coupled to the means for resetting the sampling pulse generator, second series coupled comple-mentary emitter-follow transistor pairs;
a transformer interposed between the first and the second complementary emitter-follower pairs, a network of a capacitor, diodes and a resistor operately coupled to the transformer whereby the pulse generator is adapted to generate a ringing waveform as the sampling pulses; and third series coupled complementary emitter-follower transistor pairs interposed between the output of the second series coupled complementary emitter-follower transistor pair and the galvanic isolator.
7. The sensing circuit according to claim 1, wherein the energy storage circuit is a peak detector having a diode and a capacitor 11 coupled in series with the galvanic isolator.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA274,059A CA1070410A (en) | 1977-03-16 | 1977-03-16 | Sensing circuit |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA274,059A CA1070410A (en) | 1977-03-16 | 1977-03-16 | Sensing circuit |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1070410A true CA1070410A (en) | 1980-01-22 |
Family
ID=4108169
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA274,059A Expired CA1070410A (en) | 1977-03-16 | 1977-03-16 | Sensing circuit |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1070410A (en) |
-
1977
- 1977-03-16 CA CA274,059A patent/CA1070410A/en not_active Expired
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