CA1073980A - Logic circuits and control systems incorporating such circuits - Google Patents
Logic circuits and control systems incorporating such circuitsInfo
- Publication number
- CA1073980A CA1073980A CA253,339A CA253339A CA1073980A CA 1073980 A CA1073980 A CA 1073980A CA 253339 A CA253339 A CA 253339A CA 1073980 A CA1073980 A CA 1073980A
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- Prior art keywords
- path
- input
- signal
- resistor
- amplifier
- 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
Links
- 238000012935 Averaging Methods 0.000 claims description 6
- 230000001276 controlling effect Effects 0.000 description 5
- 238000010586 diagram Methods 0.000 description 4
- 230000000694 effects Effects 0.000 description 2
- 230000005611 electricity Effects 0.000 description 2
- 230000001419 dependent effect Effects 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000000523 sample Substances 0.000 description 1
Classifications
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06G—ANALOGUE COMPUTERS
- G06G7/00—Devices in which the computing operation is performed by varying electric or magnetic quantities
- G06G7/12—Arrangements for performing computing operations, e.g. operational amplifiers
- G06G7/14—Arrangements for performing computing operations, e.g. operational amplifiers for addition or subtraction
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K19/00—Logic circuits, i.e. having at least two inputs acting on one output; Inverting circuits
- H03K19/20—Logic circuits, i.e. having at least two inputs acting on one output; Inverting circuits characterised by logic function, e.g. AND, OR, NOR, NOT circuits
- H03K19/23—Majority or minority circuits, i.e. giving output having the state of the majority or the minority of the inputs
Landscapes
- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Mathematical Physics (AREA)
- Computer Hardware Design (AREA)
- Theoretical Computer Science (AREA)
- Computing Systems (AREA)
- General Engineering & Computer Science (AREA)
- Software Systems (AREA)
- General Physics & Mathematics (AREA)
- Safety Devices In Control Systems (AREA)
Abstract
ABSTRACT
An electrical logic circuit arrangement comprising a direct-coupled operational amplifier having an input and an output, at least two control signal circuit inputs each connected to the amplifier input by way of a signal current path including a resistor, the values of the resistors being substantially equal and at least one current path including a current limiting arrangement between the resistor in that path and the amplifier input, the circuit further comprising a number of feedback paths equal to the number of signal current paths each feedback path leading separately from the amplifier output to an individual signal current path, there being one feedback path to each signal current path, each feedback path being connected to the respective input signal path at a point between the resistor of that path and the amplifier inut, this point further being located intermediate the resistor and the current limiting device of the signal input path for a path including such a device, and each feedback path including a resistor of substantially the same value as that of each signal input path resistor.
An electrical logic circuit arrangement comprising a direct-coupled operational amplifier having an input and an output, at least two control signal circuit inputs each connected to the amplifier input by way of a signal current path including a resistor, the values of the resistors being substantially equal and at least one current path including a current limiting arrangement between the resistor in that path and the amplifier input, the circuit further comprising a number of feedback paths equal to the number of signal current paths each feedback path leading separately from the amplifier output to an individual signal current path, there being one feedback path to each signal current path, each feedback path being connected to the respective input signal path at a point between the resistor of that path and the amplifier inut, this point further being located intermediate the resistor and the current limiting device of the signal input path for a path including such a device, and each feedback path including a resistor of substantially the same value as that of each signal input path resistor.
Description
~ 1073980 This invention relates to electrical logic circuits and ~o automatic electrical control systems incorporating the same.
Control of the steam inlet valves of a large steam turbine in present-day electricity generating plant presents a complex design problem. A multi-stage turbine, for example, may have four inlet valves toa high pressure stage and a similar,-or greater, number of intercept valves for intermediate pressure stage admission all requiring to be separately driven, whilst multiple sources of control parameters are involved.
The latter may comprise transducers for steam inlet temperature, boiler pressure and condenser vacuum in addition to speed detectors and controls derived from the electricity ge~erating portion of the plant.
The desirability of a control system which is substantially fail-safe for turbine control leads from primary considerations to a system having a high number of information carrying channels. A lesser number of control channels is adopted in practice, however, since the multiplicity of similar control channels in a complex system results in a eorrespondingly high number of faults within the control system itself which may lead to partial load operation of the turbine under control. This is made possible by the fact that during operation of a eontrol system incorporating a number of parallel ehannels eon~eying similar signal information, some channels are effeetively redundant and circuitry may be devised to reduee the number of ehannels required taking advantage of this redundaney.
'1073~80 ~he object of the present invention is to provide improved circuits in control systems of the tvpe described hereinabove for facilitating the adoption of redundancy techniques whilst incorporating a minimal number of circuit componen-ts of such a nature as to enhance the ability of the system to provide full continuous operation of the controlled elements whilst minimising the cost of the system.
The invention consists in an electrical logic circuit arrangement comprising a direct-coupled operational amplifier having an input and an output, at least two control signal circuit inputs each connected to the amplifier input by way of a signal current path including a resistor, the values o:F the resistors being substantially equal and at least one current path including a current limiting arrangement between the resistor in that path and the amplifier input, the circuit further comprising a number of feedback paths equal to the nu~ber of signal current paths each feedback path leading separately from the amplifier output.to an individual signal current path, there being one feedback path to each signal current path, each feedback path being connected to the respective input signal path at a point between the resistor of that path and the amplifier input, this point further being located intermediatethe resistor and the current limiting device of the signal input path for a path including such a device, and each feedback path including a resistor of substantially the same value as that of each signal input path resistor.
~he invention also consists in an automat;ic electrical control system incorporating at least one logic circuit arrange-ment as set forth in the preceding paragraph and comprising ~ ~073980 a plurality of input controlling parameters and at least one controlled output parameter, in which system at least two input - controlling parameters are applied to a logical circuit arrangement, which parameters are capable of two modes of variation with respect to each other in accordance with the presence or absence of a fault in the control system affecting a controlling parameter and the logic circuit arrangement accordingly being capable of operation in two modes corresponding to the modes of variation of the input parameters whereby control of the controlled output parameter is achieved in accordance with values of non-faulty input controlling parameters for both operational modes of any logical circult arrangement.
In the preferred form of the invention the control system according to the preceding paragraph has a logic circuit which operates in a first mode of an averaging circuit and in a second mode as a majority-voting circuit. In such a system the circuit may have a number of control signal inputs equal to the number of information channels in the system and each input signal current path includes a current limiting device. The general principle of operation of a majority-voting circuit and the particular form and application of such circuits according to the present - invention will be described hereinafter. A turbine control system requiring only three information channels whilst control-ling operation of a steam turbine with a figure for occurrence of faults requiring partial load reduction six times better than in previous systems using four information channels may be provided using majority-voting circuits according to the invention.
~073980 Accordingly, the invention further consists ir, an electrical control system for governing steam turbine operation employing at least one majority-voting circuit incorporating an electrical logic circuit as described hereinafter.
~ he invention will now be further described with reference to the accompanying drawings in whick :
Figure 1 shows a simplified circuit diagram of a conventional signal averaging circuit using a direct-coupled amplifier;
~ igure 2 shows a circuit diagram similar to ~igure 1 but incorporating a circuit modification according to the present . invention;
~igure 3 shows a circuit diagram of a majority-voting circuit accordi.ng to the present invention;
~igure 4 is a graph indicating the operating characteristics of the circuit shown - 20 in ~igure 3, : and 1~)739~30 Figure 5 is a block diagram showing a steam turbine governing electrical control system in which circuits as shown in Figure 3 are incorporated.
Referring first to Figure 1, the circuit shown is commonly used for obtaining at the output terminal O of a direct-coupled amplifier 1 a voltage equal to the average value of voltages applied to terminals A, B and C. Equal resistors of value R are included in each input line leading to a common input terminal 2 to the amplifier, as shown, whilst a resistor of value 3 is connected as a feedback path from the amplifier output terminal O to the amplifier input terminal 3.
Referring now to Figure 2, the circuit of Figure 1 is modified in accordance with the invention to enable it to give an output equal to the average of the input voltages to A, B and C for situations where the values of these voltages do not differ from each other to a marked extent (predetermined by circuit parameters), or an output signal voltage equal to the average of two of the voltages, say the voltages at B and C, plus or minus a predetermined voltage when the voltage on A
deviates to a substantial (predetermined) degree from the average of voltages B and C. The ~.agnitude of the predetermined voltage added to or subtracted from the average of voltages B and C in the latter condition is determined by the limiting value of current in the line from input terminal A to the amplifier imposed by a current limiting device Lt of which there is one in each input signal current path.
The operation of the circuit shown in Figure 2 for the averaging regime for all applied voltages to the three terminals A, B and C when these are close in value is readily explicable.
In this mode it is apparent that the current in the three input slgnal paths balance and as a result there is virtually zero current through the limiting devices Lt, which are effectively .. .
.()739~30 of low resistance. Feedback paths through resistors Rf thereforc terminate on the signal input paths at points of substantially the same potential, this being the zero potential input to the direct-coupled amplifier. Resistors RF, which are of substan-tially equal value to resistors R are therefore effectively in parallel, giving an effective feedback path resistance of RF R
If the signal voltage on terminal A deviates to any degree from those on terminals B and C, circulating currents are set up between the signal input paths from terminals A to B
and from A to C, through junction 3. When the deviation becomes sufficiently large the current limiting device Lt in the signal input path from terminal A comes into effect, limiting the current flowing through this path and isolating the resistor R
in this path and the resistor RF in the feedback path leading to it from the virtual earth point 3 at the amplifier input.
This second mode of operation is that in which the circuit operates as a majority-voting circuit since, of three input ; voltages, it is giving an output which is the average for two closely similar input voltages whilst effectively declaring the third voltage redundant and discounting it, since the constant voltage contributed at the output by the deviant input signal is relatively small.
Figure 3 shows a practical majority-voting circuit as described in which the current limiting device in each input signal path comprises a diode bridge network operating between +15V and -15V supply rails. The circuit is capable of handling three input voltages in the range -+10 volts. When the input voltages lie within -1 volt of each other, an average voltage is produced. In the majority-voting mode, when one input voltage lies outside a band of ~1 volt to -1 volt occupied by the other two voltages in the range +lOV to -lOV, the voltage produced is the average of the two similar voltages - ~ volt.
The range!of voltage in which the averaging mode operates is dependent upon the value chosen for resistors RL in the limiting circuits comprising these resistors and diode bridges sA, Bs and BC.
The above figures are illustrated in the graph shown in Figure 4 which plots the output voltage of the circuit against the input voltage on terminal A when the input voltages B and C are maintained at zero volts.
The graph shows that for values of voltage on terminal A between -1 volt and +1 volt the output voltage always lies between - ~ volt, this being the averaging range of operation of the circuit. For voltages on terminal A greater in magnitude than -1 volt (which corresponds to the limiting current being reached as determined by the current limiter), ~he output voltage is held constant at - 1 volt. Thus the output voltage never differs from the value of the equal voltage at terminals s and C by greater than 1 volt.
The control system shown in Figure 5 is applied to a steam turbine having four electrically controlled primary governor valves designated GOV.l - GOV. 4, and four electrically controlled intercept valves designated INT.l - INT.4. The latter valves are located at the inlet to the intermediate pressure turbine downstream of a reheater in a three-stage turbine system comprising a high pressure, intermediate pressure and low pressure stage as described in our British Patents Nos.
1,241,415 and 1,185,630.
Three fundamental signals for governing the turbine are derived from three main probes Pl, P2, P3 spaced at 120~
intervals on a wheel rotating with the turbine shaft. These signals, operating by way of a speed detector system, form the basis of a three channel control system operating the eight ~073980 valves of the turbine. Various other parameters, as indicated on the block schematic of Figure 5, are also accommodated in the system.
Each valve of the turbine is controlled by way of a single majority-voting circuit of the type shown in Figure 4.
In addition, three sets of triple majority-voting circuits are shown in connection with transducers for steam inlet temperature, boiler pressure and condenser vacuum. Each triple circuit - shown as a single block in Figure 5 comprises three separate circuits of the type shown in Figure 4.
Statistical estimates of the frequency with which faults necessitating partial load reduction on the turbine would occur using the system shown in Figure 5 give a figure of one fault in six years. This figure compares with estimates of one fault per annum in previous systems employing four channels and more elaborate voting circuits, the total number of faults ~that is, including faults not requiring partial load reduction) per annum, however, being approximately four in each case.
~hilst Figure 5 shows majority-voting circuits according to the invention applied in a three channel control system it should be noted that they can equally well be employed in a four channel system.
Furthermore, whilst the logic circuit shown in Figure 4 makes use of diode bridges as current limiters the invention is not limited to the use of any particular form of current limiting arrangement or device.
It should also be noted that the majority-voting circuit application of the logic circuit according to the inyention is not the sole use of the circuit. An alternative form of the circuit, for example, may readily be used as a limited range trim control in servomechanisms employing position feedback transducers inorder tominimise deadband effects.
Control of the steam inlet valves of a large steam turbine in present-day electricity generating plant presents a complex design problem. A multi-stage turbine, for example, may have four inlet valves toa high pressure stage and a similar,-or greater, number of intercept valves for intermediate pressure stage admission all requiring to be separately driven, whilst multiple sources of control parameters are involved.
The latter may comprise transducers for steam inlet temperature, boiler pressure and condenser vacuum in addition to speed detectors and controls derived from the electricity ge~erating portion of the plant.
The desirability of a control system which is substantially fail-safe for turbine control leads from primary considerations to a system having a high number of information carrying channels. A lesser number of control channels is adopted in practice, however, since the multiplicity of similar control channels in a complex system results in a eorrespondingly high number of faults within the control system itself which may lead to partial load operation of the turbine under control. This is made possible by the fact that during operation of a eontrol system incorporating a number of parallel ehannels eon~eying similar signal information, some channels are effeetively redundant and circuitry may be devised to reduee the number of ehannels required taking advantage of this redundaney.
'1073~80 ~he object of the present invention is to provide improved circuits in control systems of the tvpe described hereinabove for facilitating the adoption of redundancy techniques whilst incorporating a minimal number of circuit componen-ts of such a nature as to enhance the ability of the system to provide full continuous operation of the controlled elements whilst minimising the cost of the system.
The invention consists in an electrical logic circuit arrangement comprising a direct-coupled operational amplifier having an input and an output, at least two control signal circuit inputs each connected to the amplifier input by way of a signal current path including a resistor, the values o:F the resistors being substantially equal and at least one current path including a current limiting arrangement between the resistor in that path and the amplifier input, the circuit further comprising a number of feedback paths equal to the nu~ber of signal current paths each feedback path leading separately from the amplifier output.to an individual signal current path, there being one feedback path to each signal current path, each feedback path being connected to the respective input signal path at a point between the resistor of that path and the amplifier input, this point further being located intermediatethe resistor and the current limiting device of the signal input path for a path including such a device, and each feedback path including a resistor of substantially the same value as that of each signal input path resistor.
~he invention also consists in an automat;ic electrical control system incorporating at least one logic circuit arrange-ment as set forth in the preceding paragraph and comprising ~ ~073980 a plurality of input controlling parameters and at least one controlled output parameter, in which system at least two input - controlling parameters are applied to a logical circuit arrangement, which parameters are capable of two modes of variation with respect to each other in accordance with the presence or absence of a fault in the control system affecting a controlling parameter and the logic circuit arrangement accordingly being capable of operation in two modes corresponding to the modes of variation of the input parameters whereby control of the controlled output parameter is achieved in accordance with values of non-faulty input controlling parameters for both operational modes of any logical circult arrangement.
In the preferred form of the invention the control system according to the preceding paragraph has a logic circuit which operates in a first mode of an averaging circuit and in a second mode as a majority-voting circuit. In such a system the circuit may have a number of control signal inputs equal to the number of information channels in the system and each input signal current path includes a current limiting device. The general principle of operation of a majority-voting circuit and the particular form and application of such circuits according to the present - invention will be described hereinafter. A turbine control system requiring only three information channels whilst control-ling operation of a steam turbine with a figure for occurrence of faults requiring partial load reduction six times better than in previous systems using four information channels may be provided using majority-voting circuits according to the invention.
~073980 Accordingly, the invention further consists ir, an electrical control system for governing steam turbine operation employing at least one majority-voting circuit incorporating an electrical logic circuit as described hereinafter.
~ he invention will now be further described with reference to the accompanying drawings in whick :
Figure 1 shows a simplified circuit diagram of a conventional signal averaging circuit using a direct-coupled amplifier;
~ igure 2 shows a circuit diagram similar to ~igure 1 but incorporating a circuit modification according to the present . invention;
~igure 3 shows a circuit diagram of a majority-voting circuit accordi.ng to the present invention;
~igure 4 is a graph indicating the operating characteristics of the circuit shown - 20 in ~igure 3, : and 1~)739~30 Figure 5 is a block diagram showing a steam turbine governing electrical control system in which circuits as shown in Figure 3 are incorporated.
Referring first to Figure 1, the circuit shown is commonly used for obtaining at the output terminal O of a direct-coupled amplifier 1 a voltage equal to the average value of voltages applied to terminals A, B and C. Equal resistors of value R are included in each input line leading to a common input terminal 2 to the amplifier, as shown, whilst a resistor of value 3 is connected as a feedback path from the amplifier output terminal O to the amplifier input terminal 3.
Referring now to Figure 2, the circuit of Figure 1 is modified in accordance with the invention to enable it to give an output equal to the average of the input voltages to A, B and C for situations where the values of these voltages do not differ from each other to a marked extent (predetermined by circuit parameters), or an output signal voltage equal to the average of two of the voltages, say the voltages at B and C, plus or minus a predetermined voltage when the voltage on A
deviates to a substantial (predetermined) degree from the average of voltages B and C. The ~.agnitude of the predetermined voltage added to or subtracted from the average of voltages B and C in the latter condition is determined by the limiting value of current in the line from input terminal A to the amplifier imposed by a current limiting device Lt of which there is one in each input signal current path.
The operation of the circuit shown in Figure 2 for the averaging regime for all applied voltages to the three terminals A, B and C when these are close in value is readily explicable.
In this mode it is apparent that the current in the three input slgnal paths balance and as a result there is virtually zero current through the limiting devices Lt, which are effectively .. .
.()739~30 of low resistance. Feedback paths through resistors Rf thereforc terminate on the signal input paths at points of substantially the same potential, this being the zero potential input to the direct-coupled amplifier. Resistors RF, which are of substan-tially equal value to resistors R are therefore effectively in parallel, giving an effective feedback path resistance of RF R
If the signal voltage on terminal A deviates to any degree from those on terminals B and C, circulating currents are set up between the signal input paths from terminals A to B
and from A to C, through junction 3. When the deviation becomes sufficiently large the current limiting device Lt in the signal input path from terminal A comes into effect, limiting the current flowing through this path and isolating the resistor R
in this path and the resistor RF in the feedback path leading to it from the virtual earth point 3 at the amplifier input.
This second mode of operation is that in which the circuit operates as a majority-voting circuit since, of three input ; voltages, it is giving an output which is the average for two closely similar input voltages whilst effectively declaring the third voltage redundant and discounting it, since the constant voltage contributed at the output by the deviant input signal is relatively small.
Figure 3 shows a practical majority-voting circuit as described in which the current limiting device in each input signal path comprises a diode bridge network operating between +15V and -15V supply rails. The circuit is capable of handling three input voltages in the range -+10 volts. When the input voltages lie within -1 volt of each other, an average voltage is produced. In the majority-voting mode, when one input voltage lies outside a band of ~1 volt to -1 volt occupied by the other two voltages in the range +lOV to -lOV, the voltage produced is the average of the two similar voltages - ~ volt.
The range!of voltage in which the averaging mode operates is dependent upon the value chosen for resistors RL in the limiting circuits comprising these resistors and diode bridges sA, Bs and BC.
The above figures are illustrated in the graph shown in Figure 4 which plots the output voltage of the circuit against the input voltage on terminal A when the input voltages B and C are maintained at zero volts.
The graph shows that for values of voltage on terminal A between -1 volt and +1 volt the output voltage always lies between - ~ volt, this being the averaging range of operation of the circuit. For voltages on terminal A greater in magnitude than -1 volt (which corresponds to the limiting current being reached as determined by the current limiter), ~he output voltage is held constant at - 1 volt. Thus the output voltage never differs from the value of the equal voltage at terminals s and C by greater than 1 volt.
The control system shown in Figure 5 is applied to a steam turbine having four electrically controlled primary governor valves designated GOV.l - GOV. 4, and four electrically controlled intercept valves designated INT.l - INT.4. The latter valves are located at the inlet to the intermediate pressure turbine downstream of a reheater in a three-stage turbine system comprising a high pressure, intermediate pressure and low pressure stage as described in our British Patents Nos.
1,241,415 and 1,185,630.
Three fundamental signals for governing the turbine are derived from three main probes Pl, P2, P3 spaced at 120~
intervals on a wheel rotating with the turbine shaft. These signals, operating by way of a speed detector system, form the basis of a three channel control system operating the eight ~073980 valves of the turbine. Various other parameters, as indicated on the block schematic of Figure 5, are also accommodated in the system.
Each valve of the turbine is controlled by way of a single majority-voting circuit of the type shown in Figure 4.
In addition, three sets of triple majority-voting circuits are shown in connection with transducers for steam inlet temperature, boiler pressure and condenser vacuum. Each triple circuit - shown as a single block in Figure 5 comprises three separate circuits of the type shown in Figure 4.
Statistical estimates of the frequency with which faults necessitating partial load reduction on the turbine would occur using the system shown in Figure 5 give a figure of one fault in six years. This figure compares with estimates of one fault per annum in previous systems employing four channels and more elaborate voting circuits, the total number of faults ~that is, including faults not requiring partial load reduction) per annum, however, being approximately four in each case.
~hilst Figure 5 shows majority-voting circuits according to the invention applied in a three channel control system it should be noted that they can equally well be employed in a four channel system.
Furthermore, whilst the logic circuit shown in Figure 4 makes use of diode bridges as current limiters the invention is not limited to the use of any particular form of current limiting arrangement or device.
It should also be noted that the majority-voting circuit application of the logic circuit according to the inyention is not the sole use of the circuit. An alternative form of the circuit, for example, may readily be used as a limited range trim control in servomechanisms employing position feedback transducers inorder tominimise deadband effects.
Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An electrical logic circuit arrangement comprising a direct-coupled operational amplifier having an input and an output, at least two control signal circuit inputs each connected to the amplifier input by way of a signal current path including a resistor, the values of the resistors being substantially equal and at least one current path including a current limiting arrangement between the resistor in that path and the amplifier input, the circuit further comprising a number of feedback paths equal to the number of signal current paths each feedback path leading separately from the amplifier output to an individual signal current path, there being one feedback path to each signal current path, each feedback path being connected to the respective input signal path at a point between the resistor of that path and the amplifier input, this point further being located intermediate the resistor and the current limiting device of the signal input path for a path including such a device, and each feedback path including a resistor of substantially the same value as that of each signal input path resistor.
2. An automatic electrical control system incorporating at least one logical circuit arrangement according to Claim 1 and comprising a plurality of input controlling parameters and at least one controlled output parameter, in which system at least two input controlling parameters are applied to a logical circuit arrangement, which parameters are capable of two modes of variation with respect to each other in accordance with the presence or absence of a fault in the control system affecting a controlling parameter and the logic circuit arrangement accordingly being capable of operation in two modes corresponding to the modes of variation of the input parameters whereby control of the controlled output parameter is achieved in accordance with values of non-faulty input controlling parameters for both operational modes of any logical circuit arrangement.
3. An automatic electrical control system as claimed in Claim 2 in which a logical circuit operates in a first mode as an averaging circuit and in a second mode as a majority-voting circuit.
4, An automatic electrical control system as claimed in claim 3, wherein the circuit has a number of control signal inputs equal to the number of information channels in the system and each input signal current path includes a current limiting device.
5. An automatic electrical control system as claimed in Claim 2 in which the output parameters are arranged to control governor valves of a steam turbine.
6. An automatic electrical control system as claimed in Claim 5 in which conyrol of intercept valves of the turbine is additionally provided.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB2317175A GB1555123A (en) | 1975-05-27 | 1975-05-27 | Logic circuits and control systems incorporating such circuits |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1073980A true CA1073980A (en) | 1980-03-18 |
Family
ID=10191318
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA253,339A Expired CA1073980A (en) | 1975-05-27 | 1976-05-26 | Logic circuits and control systems incorporating such circuits |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1073980A (en) |
| GB (1) | GB1555123A (en) |
-
1975
- 1975-05-27 GB GB2317175A patent/GB1555123A/en not_active Expired
-
1976
- 1976-05-26 CA CA253,339A patent/CA1073980A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| GB1555123A (en) | 1979-11-07 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |