GB2286735A - Monitoring system and unit with fault detection - Google Patents
Monitoring system and unit with fault detection Download PDFInfo
- Publication number
- GB2286735A GB2286735A GB9402232A GB9402232A GB2286735A GB 2286735 A GB2286735 A GB 2286735A GB 9402232 A GB9402232 A GB 9402232A GB 9402232 A GB9402232 A GB 9402232A GB 2286735 A GB2286735 A GB 2286735A
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- GB
- United Kingdom
- Prior art keywords
- conductors
- impedance
- manner
- monitor unit
- constructed
- 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.)
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Classifications
-
- G—PHYSICS
- G08—SIGNALLING
- G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
- G08B29/00—Checking or monitoring of signalling or alarm systems; Prevention or correction of operating errors, e.g. preventing unauthorised operation
- G08B29/02—Monitoring continuously signalling or alarm systems
- G08B29/04—Monitoring of the detection circuits
-
- G—PHYSICS
- G08—SIGNALLING
- G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
- G08B29/00—Checking or monitoring of signalling or alarm systems; Prevention or correction of operating errors, e.g. preventing unauthorised operation
- G08B29/02—Monitoring continuously signalling or alarm systems
- G08B29/06—Monitoring of the line circuits, e.g. signalling of line faults
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- Engineering & Computer Science (AREA)
- Computer Security & Cryptography (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Testing Of Short-Circuits, Discontinuities, Leakage, Or Incorrect Line Connections (AREA)
Abstract
A monitoring system comprises a controller 1 which includes a voltage supply 4 connected to an end-of-line impedance 5 via conductors 2, 3. Fire detectors 8 are connected in parallel across the conductors. The impedance 5 comprises a resistor 6 in series with a normally-closed switch 7. Each detector 8 has an impedance in the absence of a fire which is high compared with that of the resistor 6. When a detector 8 detects a fire, its impedance falls, and the resulting fall in the voltage across conductors 2, 3 is detected by a voltage window detector 10 in the controller 1. When a detector 8 develops a fault, it momentarily reduces the impedance it presents across the conductors 2, 3. The resulting momentary drop in the voltage across the conductors 2, 3 is detected by a control means 11 which responds by opening the switch 7. The resulting rise in the voltage across the conductors is detected by the voltage window detector 10. <IMAGE>
Description
MONITORING SYSTEM AND MONITOR UNIT THEREFOR
This invention relates to a monitoring system comprising a voltage supply, an electrical impedance, a pair of electrical conductors connecting the output of the supply to the impedance, and a plurality of monitor units connected in parallel across the conductors at respective positions thereon lying between the supply and the impedance, each monitor unit being constructed to signal on said conductors in a first manner upon the occurrence of a monitored event, and at least those monitor units other than the monitor unit which is positioned on the conductors closest to the impedance being constructed to signal on said conductors in a second manner upon the occurrence of a fault therein. The invention also relates to a monitor unit for use in such a system.
A known such system is disclosed in EP-A-0253709, and may be used, for example, as a fire alarm system. In the known system, when any monitor unit senses a monitored event, e.g.
the presence of a fire, a first oscillator included in the unit is activated. This oscillator is connected to the conductors of the pair, so that its output signal appears on these conductors, signalling the occurrence of the event.
Should a fault occur in any monitor unit a second oscillator included in the unit is activated. This oscillator is also connected to the conductors of the pair and its output frequency is different from the output frequency of the first oscillator. The presence of the fault is therefore signalled on the conductors to a central station in a manner which is distinguishable from the manner in which the occurrence of the event is signalled. As mentioned In EP-A-0253709, this known system overcomes certain disadvantages of other known systems of a type in which a fault occurring in any monitor unit is signalled by the relevant monitor unit open-circuiting one of the conductors at a point corresponding to its own location.
However, it does require that the central station is capable of recognising and appropriately responding to the output signals of the two oscillators, and this is not normally a feature of central stations currently installed. One of the aforesaid disadvantages is that, unless the faulty monitor unit is the one which is positioned on the conductors closest to the electrical impedance, any monitor unit positioned closer to the electrical impedance is liable to be prevented by the open circuit from itself signalling the occurrence of a monitored event if such should occur. It is an object of the present invention to provide an alternative way of overcoming this disadvantage which does not require modification of at least some central stations which are currently installed.
According to one aspect the invention provides a monitoring system comprising a voltage supply, an electrical impedance, a pair of electrical conductors connecting the output of the supply to the impedance, and a plurality of monitor units connected in parallel across the conductors at respective positions thereon lying between the supply and the impedance, each monitor unit being constructed to signal on said conductors in a first manner upon the occurrence of a monitored event and to signal on said conductors in a second manner upon the occurrence of a fault therein, characterized in that the system includes control means having an input coupled to said electrical conductors and an output coupled to said electrical impedance, said control means being constructed to change said electrical impedance from a first non-zero value to a second non-zero value in response to signalling on said conductors in said second manner.
According to another aspect the invention provides a monitor unit for use in such a system, the unit having first and second terminals for connection to respective said electrical conductors and being constructed to signal between said terminals in a first manner upon the occurrence of a monitored event and to signal between said terminals in a second manner upon the occurrence of a fault therein, the unit having a further terminal and including a controllable switch connected between said second terminal and said further terminal and control means having an input coupled to said first and second terminals and an output coupled to a control input of said switch, the control means being constructed to respond to a signal occurring in said second manner between said first and second terminals by opening said switch.
According to another aspect the invention provides a monitoring system comprising a voltage supply, an electrical impedance, a pair of electrical conductors connecting the output of the supply to the impedance, and a plurality of monitor units connected in parallel across the conductors at respective positions thereon lying between the supply and the impedance, each monitor unit being constructed to signal on said conductors in a first manner upon the occurrence of a monitored event, and at least those monitor units other than the monitor unit which is positioned on the conductors closest to the impedance being constructed to signal on said conductors in a second manner upon the occurrence of a fault therein, characterized in that the system includes control means having an input coupled to said electrical conductors and an output coupled to said electrical impedance, which control means is constructed to change said electrical impedance from a first non-zero value to a second non-zero value in response to signalling on said conductors in said second manner, and in that the monitor unit which is positioned on the conductors closest to the impedance has an output coupled to said electrical impedance and is constructed to change said electrical impedance from the first non-zero value to the second non-zero value in response to the occurrence of a fault in this monitor unit.
The inventor has recognised that, if the occurrence of a fault in a monitor unit is arranged to change the impedance of the loop comprising the conductors of the pair and the said electrical impedance by changing said electrical impedance from one non-zero value to another non-zero value (where the second non-zero value may correspond, for example, to an open circuit) rather than by inserting an open circuit in the loop at the location of the relevant monitor unit, the operation of all the other monitor units, in particular the signalling capabilities thereof, need not be affected.
Embodiments of the invention will be described, by way of example, with reference to the accompanying diagrammatic drawings in which
Fig. 1 shows a monitoring system and
Fig. 2 shows a possible construction for a monitor unit included in the system of Fig. 1 in more detail.
In Fig. 1 a monitoring system comprises a central station or controller 1 and a pair of conductors 2, 3 which connect the output of a d.c. voltage supply 4 included in the controller 1 to an end-of-line terminating impedance 5 in the form of a resistor 6 connected in series with a controllable normally-closed switch 7. The conductors 2, 3 pass through a monitored zone in which is located a plurality of monitor units 8A, 8B, 8C connected in parallel across the conductors 2, 3 at respective positions thereon. The voltage supply 4 has an internal resistance 9.
In normal quiescent operation each monitor unit 8, which is, in the present example, a fire detector unit, has a high impedance compared with that of the terminating impedance 5 (the switch 7 being closed). The current drawn from the source 4 by the units 8 collectively is therefore low compared with the current drawn by the terminating impedance 5, and the voltage across the conductors 2, 3 adopts a value V1. Upon the occurrence of a monitored event, in the present example a fire, one or more of the units 8 detects this and is constructed to respond by changing the impedance it presents to the conductors 2, 3 to a lower value. The current drawn from the supply 4 therefore increases and the voltage across the conductors 2, 3 adopts a new value V2 which is lower than V1.
The voltage across the conductors 2, 3 is monitored by a voltage monitoring arrangement 10 included in the controller 1. Arrangement 10, which may comprise a set of voltage comparators one input of each of which is fed with the voltage on the conductor 2 and the other input of each of which is fed with an appropriate reference voltage, is constructed to indicate whether the voltage between the conductors 2 and 3 (a) lies within a first range, (b) lies within a second range which adjoins but does not overlap the first range, (c) lies above both of these ranges, or (d) lies below both of these ranges respectively.The first range is chosen to include all the voltages, e.g. voltage V2, which can occur in fault-free operation in the event of detection of a fire by one or more of the units 8, but to exclude the voltages, e.g. voltage V1, which can occur in fault-free operation when the system is in the quiescent state (no fire detected) and also to exclude the voltages which can occur should a short-circuit occur between the conductors 2 and 3. The second range, which is higher than the first, is chosen to include all the voltages, e.g.
voltage V1, which can occur in fault-free operation when the system is in the quiescent state (no fire detected) but to exclude the voltages which can occur in the event of an open circuit occurring in the loop comprising the conductors 2 and 3 and the terminating impedance 5. Indications by arrangement 10 of the situations (a), (b), (c) and (d) are therefore indications of the presence of a fire, of fault-free operation and the absence of a fire, of a break in the loop 2, 5, 3, and of a short-circuit between the conductors 2 and 3, respectively.
As so far described the operation of the system of Fig.
1 is conventional (although the terminating impedances in conventional systems do not include switches such as switch 7). However, the system of Fig. 1 also includes control means 11 which has an input 12A, 12B connected to the conductors 2, 3 and an output 13 connected to a control input 14 of the terminating impedance 5. The input 14 in fact constitutes the control input of the controllable switch 7.
Should a fault occur in any of the monitoring units 8 the relevant unit is arranged to momentarily reduce the impedance it presents to the conductors 2, 3. The voltage across these conductors therefore momentarily decreases and control means 11 is constructed to detect this momentary decrease and respond by generating a signal at it output 13, this signal being such as to open switch 7. The terminating impedance 5 therefore increases to a very high value and the voltage across the conductors 2 and 3 therefore increases to a steady value V3 which is such as to be indicative of an open circuit in the loop 2, 5, 3. Arrangement 10 indicates the presence of this voltage and hence the presence of a fault in the system (either a fault in one of the units 8 or a break in one or both of the conductors 2, 3).It will be noted that, in the event of the fault being in one of the units 8, the remaining units 8 are still capable of signalling the presence of a fire to the arrangement 10, because each unit is still connected to the arrangement 10 and the supply 4 via the conductors 2 and 3.
Fig. 2 shows a possible construction for each of the units 8 of Fig. 1, this construction being such that each unit effectively includes control means similar to the control means 11 of Fig. 1 and a switch similar to switch 7 of Fig.
1 so that the control means and switch included in that unit which is positioned on the conductors 2, 3 closest to the terminating impedance 5 can actually be used as the control means 11 and switch 7.
The monitor unit shown in fig. 2 comprises a fire detector arrangement 15 terminals 16 and 17 of which are connected to the conductors 2 and 3 respectively. Detector arrangement 15 is constructed in known manner in such a way that the resistance it provides between the terminals 16 and 17 decreases in the presence of a fire. Detector arrangement 15 furthermore has an output 18 at which a logic level appears indicative of whether or not there is a fault in the arrangement 15. To this end the arrangement 15 may be arranged to periodically perform a self-test routine under microcomputer control, the result of this routine being signalled at the output 18. Output 18 is coupled both to the control input 19 of a switch 20 via a monostable multivibrator 21 and to one input of an OR-gate 22. Switch 20 is connected in series with a resistor 29 between the terminals 2 and 3.
Multivibrator 21 has an astable period of, for example, 20mS.
Should a fault occur in the arrangement 15 the resulting logic level, in the present example logic "1", on output 18 triggers the multivibrator 18 which, in turn, momentarily closes the switch 20 for the duration of its astable period. Thus the impedance presented by the monitor unit across the conductors 2 and 3 is reduced to the resistance of resistor 29 for, in the present example, 20mS, and the voltage across the conductors is reduced for the same period. Resistor 29 may have a resistance of a few hundred ohms.
The monitor unit of Fig. 2 also includes control means 25 which are constructed to operate in the same way as control means 11 of Fig. 1. Control means 25 has an input 26A, 26B connected to the conductors 2 and 3 and an output 27 and is constructed to respond to the occurrence of a reduction in voltage across the conductors 2 and 3 for a period of substantially 20mS by generating logic "1" at its output 27, which output is connected to the control input 23 of a switch 28. To this end control means 25 may be constituted by an appropriately programmed microcomputer, for example the same microcomputer which performs the self-test routine in the detector arrangement 15. Switch 28 is connected between the conductor 3 and an output 24 and is normally closed.
Should a fault occur in the detector arrangement 15, resulting in a logic "1" at its output 18, or should control means 25 detect the occurrence of a reduction in voltage across the conductors 2 and 3 for a period of substantially 20mS, resulting in a logic "1" on its output 27, the resulting logic "1" from the OR-gate 22 opens switch 28.
When the construction of Fig. 2 is used for the monitor units 8A and 8B of Fig. 1 the output 24 is not used. However, when the construction of Fig. 2 is used for the monitor unit 8C the output 24 is connected to the lower end of resistor 6; the switch 28 then constitutes the switch 7 of Fig. 1 and the control means 25 constitutes the control means 11 of Fig. 1.
It will be evident that many modifications may be made to the embodiment described, within the scope of the invention as defined by the claims. For example, insofar as the construction of Fig. 2 is used for the monitor unit 8C of Fig.
1 the switch 20 and monostable multivibrator 21 may be omitted, the occurrence of a fault in the unit 8C being used directly to open the switch 28 rather than via signalling on the conductors 2 and 3. Similarly, insofar as the construction of Fig. 2 is used for the monitor units 8A and 8B of Fig. 1 the control means 25, OR-gate 22 and switch 28 may be omitted. However the construction of Fig. 2 offers the advantage of being applicable to each of the units 8A, 8B and 8C while making it unnecessary to provide a separate control means 11.
Although as described the signalling of a fault in one of the monitor units 8 is achieved by momentarily reducing the impedance presented across the conductors 2 and 3 it will be appreciated that other forms of signalling may be employed, for example the application to the conductors 2 and 3 of a signal of a specific frequency by means of an oscillator having its output connected to the conductors 2, 3 or by opening and closing the switch 20 at a specific rate. A similar comment applies to the signalling on the conductors of the presence of a fire, which may be achieved in many different ways.
The output of the voltage supply 4 may be a.c. rather than d.c., enabling the resistor 6 to be replaced, for example, by a capacitor. However, such a modification will in many cases necessitate the provision of a rectifier and smoothing unit in each unit 8, so is not preferred.
Although as described the occurrence of a fault in a monitoring unit results in a change in the line-terminating impedance 5 from a given non-zero value to substantially an open-circuit it will be appreciated that this is not essential; the change may, for example, be arranged to be to a higher but still finite value or even to a lower value.
The invention has been described in the context of a monitoring system for the presence of a fire. However, it will be evident that it is also applicable to monitoring systems for other kinds of event, for example temperature or pressure monitoring systems.
Claims (8)
1. A monitoring system comprising a voltage supply, an electrical impedance, a pair of electrical conductors connecting the output of the supply to the impedance, and a plurality of monitor units connected in parallel across the conductors at respective positions thereon lying between the supply and the impedance, each monitor unit being constructed to signal on said conductors in a first manner upon the occurrence of a monitored event and to signal on said conductors in a second manner upon the occurrence of a fault therein, characterized in that the system includes control means having an input coupled to said electrical conductors and an output coupled to said electrical impedance, said control means being constructed to change said electrical impedance from a first non-zero value to a second non-zero value in response to signalling on said conductors in said second manner.
2. A monitoring system comprising a voltage supply, an electrical impedance, a pair of electrical conductors connecting the output of the supply to the impedance, and a plurality of monitor units connected in parallel across the conductors at respective positions thereon lying between the supply and the impedance, each monitor unit being constructed to signal on said conductors in a first manner upon the occurrence of a monitored event, and at least those monitor units other than the monitor unit which is positioned on the conductors closest to the impedance being constructed to signal on said conductors in a second manner upon the occurrence of a fault therein, characterized in that the system includes control means having an input coupled to said electrical conductors and an output coupled to said electrical impedance, which control means is constructed to change said electrical impedance from a first non-zero value to a second non-zero value in response to signalling on said conductors in said second manner, and in that the monitor unit which is positioned on the conductors closest to the impedance has an output coupled to said electrical impedance and is constructed to change said electrical impedance from the first non-zero value to the second non-zero value in response to the occurrence of a fault in this monitor unit.
3. A system as claimed in Claim 1 or Claim 2, wherein the second non-zero value is higher than the first non-zero value.
4. A system as claimed in any preceding claim, wherein the signalling on the conductors in the second manner is achieved by the relevant monitor unit decreasing the impedance presented thereby to said conductors for a first period of time and the signalling on the conductors in the first manner is achieved by the relevant monitor unit decreasing this impedance for a longer period of time.
5. A monitoring system substantially as described herein with reference to Fig. 1 of the drawings or to Figs. 1 and 2 of the drawings.
6. A monitor unit for use in a system as claimed in Claim 1, the unit having first and second terminals for connection to respective said electrical conductors and being constructed to signal between said terminals in a first manner upon the occurrence of a monitored event and to signal between said terminals in a second manner upon the occurrence of a fault therein, the unit having a further terminal and including a controllable switch connected between said second terminal and said further terminal and control means having an input coupled to said first and second terminals and an output coupled to a control input of said switch, the control means being constructed to respond to a signal occurring in said second manner between said first and second terminals by opening said switch.
7. A monitor unit as claimed in Claim 6, wherein the firstmentioned signalling between said terminals in the second manner is achieved by the monitor unit decreasing the impedance between said terminals for a first period of time and the signalling between said terminals in the first manner is achieved by the monitor unit decreasing this impedance for a longer period of time.
8. A monitor unit substantially as described herein with reference to Fig 2 of the drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9402232A GB2286735B (en) | 1994-02-05 | 1994-02-05 | A monitoring system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9402232A GB2286735B (en) | 1994-02-05 | 1994-02-05 | A monitoring system |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB9402232D0 GB9402232D0 (en) | 1994-03-30 |
| GB2286735A true GB2286735A (en) | 1995-08-23 |
| GB2286735B GB2286735B (en) | 1998-03-04 |
Family
ID=10749932
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9402232A Expired - Fee Related GB2286735B (en) | 1994-02-05 | 1994-02-05 | A monitoring system |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2286735B (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2897968A1 (en) * | 2006-02-24 | 2007-08-31 | Airbus France Sas | Concerned area`s fire detection system for aircraft, has two detectors connected to terminals of fire detection unit and providing respective values of electrical magnitude in their determined state, where two values differ from each other |
| WO2009132717A1 (en) | 2008-04-28 | 2009-11-05 | Robert Bosch Gmbh | Monitoring device for functionally monitoring a reporting system reporting system and method for monitoring |
| FR2932917A1 (en) * | 2008-06-23 | 2009-12-25 | Legrand France | Safety installation, has central monitoring station connected to end of double-wire line, and time delay circuit for placing, after triggered, terminal connection formed of two parallel branches, in impedance state during monitoring phase |
| EP2169645A1 (en) * | 2008-09-25 | 2010-03-31 | Novar GmbH | Test of reporting lines on a danger reporting assembly |
| FR3023376A1 (en) * | 2014-07-07 | 2016-01-08 | Snecma | METHOD FOR DETECTING A FAILURE OF AT LEAST ONE SENSOR |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0253709A1 (en) * | 1986-07-11 | 1988-01-20 | FERCO INTERNATIONAL Usine de Ferrures de BÀ¢timent Société à responsabilité limitée | Monitoring installation with detectors in the form of a loop |
-
1994
- 1994-02-05 GB GB9402232A patent/GB2286735B/en not_active Expired - Fee Related
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0253709A1 (en) * | 1986-07-11 | 1988-01-20 | FERCO INTERNATIONAL Usine de Ferrures de BÀ¢timent Société à responsabilité limitée | Monitoring installation with detectors in the form of a loop |
Cited By (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2897968A1 (en) * | 2006-02-24 | 2007-08-31 | Airbus France Sas | Concerned area`s fire detection system for aircraft, has two detectors connected to terminals of fire detection unit and providing respective values of electrical magnitude in their determined state, where two values differ from each other |
| WO2007096523A3 (en) * | 2006-02-24 | 2007-10-11 | Airbus France | Fire detection system and aircraft equipped with such a system |
| US8094030B2 (en) | 2006-02-24 | 2012-01-10 | Airbus Operations Sas | Fire detection system and aircraft equipped with such a system |
| WO2009132717A1 (en) | 2008-04-28 | 2009-11-05 | Robert Bosch Gmbh | Monitoring device for functionally monitoring a reporting system reporting system and method for monitoring |
| US20110050440A1 (en) * | 2008-04-28 | 2011-03-03 | Stefan Kriz | Monitoring device for functionally monitoring reporting system, reporting system, and method for monitoring |
| CN102016946A (en) * | 2008-04-28 | 2011-04-13 | 罗伯特·博世有限公司 | Monitoring device for functionally monitoring a reporting system reporting system and method for monitoring |
| US8456315B2 (en) | 2008-04-28 | 2013-06-04 | Robert Bosch Gmbh | Monitoring device for functionally monitoring reporting system, reporting system, and method for monitoring |
| CN102016946B (en) * | 2008-04-28 | 2014-12-17 | 罗伯特·博世有限公司 | Monitoring device for functionally monitoring a reporting system, reporting system and method for monitoring |
| FR2932917A1 (en) * | 2008-06-23 | 2009-12-25 | Legrand France | Safety installation, has central monitoring station connected to end of double-wire line, and time delay circuit for placing, after triggered, terminal connection formed of two parallel branches, in impedance state during monitoring phase |
| EP2169645A1 (en) * | 2008-09-25 | 2010-03-31 | Novar GmbH | Test of reporting lines on a danger reporting assembly |
| FR3023376A1 (en) * | 2014-07-07 | 2016-01-08 | Snecma | METHOD FOR DETECTING A FAILURE OF AT LEAST ONE SENSOR |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2286735B (en) | 1998-03-04 |
| GB9402232D0 (en) | 1994-03-30 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20090205 |