GB2110386A - Apparatus for monitoring the state of a multi-state device - Google Patents
Apparatus for monitoring the state of a multi-state device Download PDFInfo
- Publication number
- GB2110386A GB2110386A GB08135774A GB8135774A GB2110386A GB 2110386 A GB2110386 A GB 2110386A GB 08135774 A GB08135774 A GB 08135774A GB 8135774 A GB8135774 A GB 8135774A GB 2110386 A GB2110386 A GB 2110386A
- Authority
- GB
- United Kingdom
- Prior art keywords
- state
- switch
- signal
- monitoring
- processor
- 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.)
- Granted
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/28—Testing of electronic circuits, e.g. by signal tracer
- G01R31/2832—Specific tests of electronic circuits not provided for elsewhere
- G01R31/2836—Fault-finding or characterising
- G01R31/2837—Characterising or performance testing, e.g. of frequency response
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
- H03K17/18—Modifications for indicating state of switch
Landscapes
- Engineering & Computer Science (AREA)
- General Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Testing And Monitoring For Control Systems (AREA)
Abstract
An input channel of a process control system for monitoring a status-indicating switch is also connected to another circuit for selectively supplying signals representative of each state of the switch. Successive application of each signal enables the processor to check for a corresponding change in the signal supplied by the input channel, thereby confirming integrity of the channel irrespective of the current state of the switch. <IMAGE>
Description
SPECIFICATION
Apparatus for monitoring the state of a multistate device
This invention relates to apparatus for monitoring the state of a multi-state device such as a switching device.
Switching devices such as relay contacts are used extensively in, for example, industrial process control systems to provide remote indication of the status of such equipment as valves. It is important that the occurrence of a fault in the circuits used to monitor the states of such switching devices should not cause or permit damage to the plant being controlled by the system. One conventional way of ensuring this is to provide duplicate or redundant monitoring circuits, and compare the outputs of these circuits for any differences. However, this approach is costly in terms of components used, and, in the event of a circuit failure which leaves the output of the circuit stuck in its usual state, cannot detect the failure until the switching device being monitored changes in its own state.
According to one aspect of this invention there is provided apparatus for monitoring the state of a multi-state device, comprising sensing means arranged to sense the state of said device, first signal supply means arranged selectively to supply a first signal corresponding to a first state of said device, second signal supply means arranged selectively to supply a second signal corresponding to a second state of said device, and means for coupling signals from said first and second supply means to said sensing means irrespective of the state of said device, whereby the ability of said sensing means to detect both said states of said device can be tested.
Apparatus in accordance with this invention will now be described, by way of example, with reference to the accompanying drawing, in which: Figure 1 is a circuit diagram of one form of the apparatus; and
Figure 2 is a circuit diagram of another form of the apparatus.
The invention is for use in, for example, a process control system, in which a central processor (typically a computer) monitors various parameters indicative of the progress of an industrial process, and selectively operates equipment, such as valves, heaters and pumps, to regulate the process. In such circumstances, information about the position of, for example, a valve may be signalled to the processor by a switch associated with the valve. Typically, the valve may be operated by energisation of a relay having contacts which switch current to the value actuator, and the relay may have another set of contacts signalling the state of energisation of the relay to the processor. Alternatively, the movement of the valve may be arranged to operate directly a microswitch monitored by the processor.
Thus, referring to Figure 1, the processor (not shown) controls an actuator 10 which operates an item of equipment (not shown). The status of this equipment is indicated by the state of a switch 12 connected to a +V Volts supply and operated in conjunction with the equipment, and the state of this switch 12 is monitored in the processor via a filter 14 and an opto-coupler 16 which provides galvanic isolation.
If this monitoring arrangement develops a fault, the processor will of course no longer be able to sense the status of the equipment in question. Furthermore, the monitoring arrangement may fail such that the signal to the processor remains in the condition it normally assumes. Thus, for example, the switch 12 may normally be open, in which case the light-emitting diode in the opto-coupler 16 would normally be de-energised. Failure of the light-emitting diode would not then produce any change in the signal to the processor while the switch 12 remained open. Consequently the fault may not be discovered for some time, or, worse, only when the absence of the expected signal from the optocoupler caused malfunction of the industrial process.
Accordingly, and as shown in Figure 1, the processor can selectively energise two more opto-couplers 1 8 and 20. The first opto-coupler
18 is arranged to turn a transistor 22 on, thereby applying +V volts to the opto-coupler 16 via a diode 24 and simulating the signal from the switch 12 in its closed or on state. Conversely, the second opto-coupler 20 is arranged to turn a transistor 26 on, applying zero volts to the optocoupler 16 via a diode 28 and simulating the signal from the switch 12 in its open or off state.
The diodes 24 and 28 provide a wired-OR connection, allowing the simulated signals from the transistors 22 and 26 to be applied to the opto-coupler 1 6 irrespective of the current state of the switch 12.
Thus the integrity of the arrangement for monitoring the switch 12 can be tested at any time by energising the opto-couplers 18 and 20 in turn, thereby temporarily changing the state of the drive to the opto-coupler 1 6. Failure of the signal from this opto-coupler 1 6 to the processor to change in response to either test signal
indicates that a fault has developed.
The same test signals from the transistors 22
and 26 can be applied to other opto-couplers like the device 1 6 in other switch monitoring
channels.
Figure 2 shows another way of implementing the invention. Referring to Figure 2, a relay coil
30, having associated contacts 32 for controlling
plant equipment, is selectively energised by the
central processor via an open-collector
buffer/inverter 34. The current state of the relay
30 is monitored by a comparator 36 receiving the
output of the buffer/inverter 34 on one input and
a reference signal on its other input. The reference
signal is normally OV from an electronic switch
38, but can selectively be made +V volts under the
control of the processor by tandem operation of the switch 38 and a second electronic switch 40 coupled to the +V volts supply.
In order to check the integrity of the comparator 36, to ensure for example that it has not failed to the state corresponding to the normal state of energisation of the relay 30, the electronic switches 38 and 40 are periodically operated momentarily, thereby changing the reference signal to the comparator 36. The processor simultaneously monitors the comparator output to check for a corresponding change in the signal there. Lack of any such change would indicate a malfunction.
It is also possible to monitor the integrity of the relay coil 30, by momentarily changing the input signal to the buffer/inverter 34. This should cause a corresponding change at the output of the buffer/inverter 34, which will be sensed by the comparator 36 (if the change is made appropriately brief, the inertia of the magnetic field in the relay 30 will prevent any corresponding change in the state of the contacts 32). However, should the relay coil 30 have become open-circuit, the open-collector output of the buffer/inverter 34 will not be able to change in voltage, since it then has no output load (equivalent to a pull-up resistor in logic circuit terms). Accordingly, the brief change in input signal will not be accompanied by any change in the signal from the comparator 36, indicating that a fault has occurred.
Claims (1)
- Claim1. Apparatus for monitoring the state of a multi-state device, comprising sensing means arranged to sense the state of said device, first signal supply means arranged selectively to supply a first signal corresponding to a first state of said device, second signal supply means arranged selectively to supply a second signal corresponding to a second state of said device, and means for coupling signals, from said first and second supply means to said sensing means irrespective of the state of said device, whereby the ability of said sensing means to detect both said states of said device can be tested.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB08135774A GB2110386B (en) | 1981-11-26 | 1981-11-26 | Apparatus for monitoring the state of a multi-state device |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB08135774A GB2110386B (en) | 1981-11-26 | 1981-11-26 | Apparatus for monitoring the state of a multi-state device |
Publications (2)
Publication Number | Publication Date |
---|---|
GB2110386A true GB2110386A (en) | 1983-06-15 |
GB2110386B GB2110386B (en) | 1985-09-25 |
Family
ID=10526183
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
GB08135774A Expired GB2110386B (en) | 1981-11-26 | 1981-11-26 | Apparatus for monitoring the state of a multi-state device |
Country Status (1)
Country | Link |
---|---|
GB (1) | GB2110386B (en) |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4631693A (en) * | 1983-02-15 | 1986-12-23 | G.D. Societa Per Azioni | System for monitoring the operation of output transducers of a central control and monitoring unit for machines and/or devices usable in production and/or product packaging lines |
FR2692677A1 (en) * | 1992-06-22 | 1993-12-24 | Moulinex Sa | Sensor detection system and method for implementing a device for verifying the operation of this detection system. |
DE10314261B4 (en) * | 2003-03-29 | 2007-01-11 | Aufzugswerke M. Schmitt & Sohn Gmbh & Co. | Bridge circuit to query a switch |
-
1981
- 1981-11-26 GB GB08135774A patent/GB2110386B/en not_active Expired
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4631693A (en) * | 1983-02-15 | 1986-12-23 | G.D. Societa Per Azioni | System for monitoring the operation of output transducers of a central control and monitoring unit for machines and/or devices usable in production and/or product packaging lines |
FR2692677A1 (en) * | 1992-06-22 | 1993-12-24 | Moulinex Sa | Sensor detection system and method for implementing a device for verifying the operation of this detection system. |
EP0575912A1 (en) * | 1992-06-22 | 1993-12-29 | Moulinex S.A. | Method and device for verifying functioning of a detection system with sensor |
US5450059A (en) * | 1992-06-22 | 1995-09-12 | Moulinex (Societe Anonyme) | Detection system and method for the verification of the functioning of the detection system by instantaneous comparison of the state of a node on a receptor and a node on a detector |
DE10314261B4 (en) * | 2003-03-29 | 2007-01-11 | Aufzugswerke M. Schmitt & Sohn Gmbh & Co. | Bridge circuit to query a switch |
Also Published As
Publication number | Publication date |
---|---|
GB2110386B (en) | 1985-09-25 |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
PCNP | Patent ceased through non-payment of renewal fee |