GB2173618A - Alarm monitoring installation - Google Patents

Abstract

The alarm monitoring network 1 consists of a central control unit 2 and alarm modules e.g. 3,4,5 and 6 linked together in parallel configuration by a transmission line 7 of two coaxial cables 8 and 9. To address the modules, central control unit 2 outputs a pulsed voltage signal to the transmission line 7 and notes the consequent current variations caused by the modules reacting in turn. Each module is addressed by two pulses, allowing measurement firstly of the line alone, and secondly of the line together with the sensing circuitry of the module. The pulsed signal may be used to give some modules commands additional to the addressing instructions, e.g. further interrogation of its condition or instructions on changing its mode of operation. <IMAGE>

Description

SPECIFICATION Alarm monitoring installation The present invention relates to an installation for monitoring the condition of a number of alarms, and to a method of operating such an installation.

The present invention provides an alarm monitoring installation comprising: a central control unit; a plurality of alarm modules connected to the central control unit along a common line; means to address each of the alarm modules in order to determine the condition of each alarm module; and means to effect measurement of the line characteristics during addressing of an alarm module.

In this way, the installation can take into account any variations in the line characteristics which might occur due to changes in ambient temperatures, or due to equipment deterioration.

Preferably, the measurement means effects, in use, measurement of the characteristics relating to the line alone, and measurement of the characteristics relating to the line and to the module together.

By effecting these measurements and thereafter subtracting the two resultant values to produce an indication of the characteristics for the module alone, the latter can be determined accurately even when it is only a small fraction of the line characteristic.

Preferably, the measurement means incorporates: means to produce a signal formed of a sequence of pulses incorporating a number of pulses for each module; and each module having means to detect the appropriate pulses and to switch in the sensing circuitry during the addressing operation of that module. Preferably the signal-production means provides two pulses for each module, and the module has means to switch in the sensing circuitry upon detection of the second pulse.

The present invention also provides a method for operating an alarm monitoring installation having a plurality of alarm modules connected to a central control unit via a common line, the method comprising: addressing each of the alarm modules in order to determine the condition of each module; and effecting measurement of the line characteristics during addressing of a module.

Preferably, the method comprises, in addressing a module, measuring the characteristics relating to the line alone and then measuring the characteristics relating to the line and to the module together.

Preferably, the method comprises: producing a signal formed of a sequence of pulses incorporating a number of pulses for each module; each module detecting the appropriate pulses and switching in the sensing circuitry during the addressing operation of that module. Advantageously, the method comprises: providing two pulses for each module; a module switching in the sensing circuitry upon detection of the second pulse.

According to another aspect, the present invention also provides an alarm monitoring installation comprising: a central control unit; a plurality of alarm modules connected to the central control unit along a common line, each alarm module being assigned a specific detection function; means to address each of the modules in order to determine the condition of the module concerning the specific detection function; and means to command a module, during the addressing function, to perform an additional function.

Preferably the system comprises: means, in the addressing means, to send a sequence of pulses along the common line; and means in a module, to detect the pulses appropriate to it and to determine any which command it to perform an additional function.

Preferably, the command means includes: means to produce pulses of different format to the standard pulses used in addressing the modules; and means, in the sensor(s), to distinguish the pulses of the command means from the standard addressing pulses. For example, the command pulses may be of a different amplitude to the standard pulses.

The additional function may incorporate additional sensing or it may incorporate interrogation of the module as to its mode of operation.

According to this aspect the present invention also provides a method for operating an alarm monitoring installation having a plurality of alarm modules having a specific detection function and connected to a central control unit via a common line, the method comprising: addressing each of the modules in order to determine the condition of the module concerning the specific detection function; and commanding a module, during the addressing step, to perform an additional function.

Preferably the method also comprises; in the addressing step, sending a sequence of pulses along the common line; and a module detecting the pulses appropriate to it and determining any pulses which command itto perform an additional function.

Preferably the method also comprises: in the command step, producing pulses of different format to the standard pulses used in addressing the modules; and at least one of the modules distinguishing the command pulses from the standard addressing pulses.

According to a further aspect, the present invention also provides an alarm monitoring installation comprising: a plurality of alarm modules connected to a central control unit along a common line; means to address each of the modules in order to determine the condition of the module; each of the modules having means to operate a relay to provide a line termination if a fault occurs in the common line between that module and the adjacent module downstream.

In this way, any line fault can be isolated in order that operation of the remaining sensors can be maintained until rectification of the fault can occur.

Preferably the system has means to achieve similar action on the other side of the fault.

The central control unit may also have means to send pulses down both sections of a common line when a fault occurs.

According to this aspect, the present invention also provides a method of operating an alarm monitoring installation having a plurality of alarm modules connected to a central control unit with a common line, the method comprising: addressing each of the modules in order to determine the condition of the module; and operating a relay, which provides a line termination, at a module adjacent a fault occurring in the common line.

Preferably, the method comprises thereafter sending the pulses down both sections of the common line towards the fault.

In order that the invention may more readily be understood, a description is now given, by way of example only, reference being made to the accompanying drawings, in which: Figure lisa block diagram of an installation embodying the present invention; Figure 2 is a schematic diagram of a signal used in the installation of Figure 1; Figure 3 is a block diagram of an alarm module used in the installation of Figure 1; Figure 4 is a circuit diagram of an alarm module used in the installation of Figure 1.

Figure 5 is a block diagram of an alarm module used in another form of installation embodying the present invention; Figure 6 is a circuit diagram of the module of Figure 5; and Figure 7 is a schematic diagram of a signal used in the installation of Figures 5 and 6.

The alarm monitoring network 1 (shown in Figure 1) consists of a central control unit 2 and a thirty-two alarm modules (only four, designated 3,4,5 and 6, being shown) which are linked together by a transmission line 7 formed of two coaxial cables 8 and 9.

Each module is connected between the two coaxial cables, so thatthe modules are arranged in a parallel configuration.

In order to address the modules, the central control unit 2 outputs a pulsed voltage signal to the transmission line 7 and notes the consequent current variations caused by the modules reacting in turn. Each module has a counter which is incremented by each of the pulses, and each module compares its counter reading with its address identity; when the two values are the same, the module's condition is measured.

The signal output by unit 2 (see Figure 2) consists of a first synchronising section of 80 milliseconds duration followed by a sequence of 64 pulses each of 3 milliseconds duration and separated by intervals each of 7 milliseconds duration. Thus, during the first synchronising section the line voltage is maintained ata constant level in order to reset to zero all the counters in the modules and to ensure that all the modules are synchronised in preparation for the sequence of pulses.Each of the modules is addressed by a pair of the pulses in the sequence; thus the first module, referenced 3, has an address identity of "one" so that when its counter reading increments to "one" in response to the first pulse A of the sequence, module 3 is alerted but its sensing circuitry remains disabled until the next pulse, B, is received, whereupon the sensing circuitry of module 3 is switched into connection with the transmission line 7.In this way, the central control unit 2 utilizes the 7 millisecond time interval between pulses A and B to measure the current drawn by the transmission line 7 with module 3 alerted but its sensing circuitry disabled (all the other modules not being alerted or enabled); then unit 2 uses the 7 millisecond time interval immediately after pulse B to measure the current drawn by the transmission line with the sensing circuitry of module 3 enabled (all the other modules being in the same condition as before). The difference between these two values of current provides a measurement of the current drawn due to the sensing circuitry of module 3 and therefore an indication of its condition.

This procedure has two significant advantages: firstly it eliminates any discrepancies that might otherwise occur due to variations in the current drawn by the line itself (for example variations caused by temperature changes or equipment deterioration); secondly, it enables accurate measure ment of the sensing current drawn, which is a parameter small (of the order of 20 milliamps) in relation to the current drawn by the transmission line 7 itself (of the order of 300 milliamps).

Transmission down line 7 of the third pulse, C, results in all the modules counters further in crementing their readings by one (hence to "three"); only in module 4 will there be any consequent action, caused by its counter reading now corres ponding to its address identity of "three". Thus module 4 will be alerted and its sensing circuitry will be enabled once the next pulse, D, is detected by monitor 4. Measurement of the currents drawn by line 7 alone, and then line 7 and module 4 together, are achieved in the same manner as described in relation to module 3.

One distinction is that pulse D is of greater depth than the other pulses, this feature being used to give the module commands additional to the addressing instructions; such commands may involve interro gating the module on further aspects of its operating condition or its sensing condition, or instructing itto change its mode of operation, for example its sensitivity when sensing. Thus any pulse with increased depth of the form of pulse D can be used to achieve two functions, namely that of addressing the module for normal sensing condition measure ment and also that of sending additional commands to the module. Thus, in all the modules, the counters and the circuitry causing the alerting and enabling operations are sensitive to pulses of 10 volts or more depth, while some (or all) of the modules have additional circuitry concerned with the second func tion and sensitive only to pulses of depth significant ly greater than 10 volts (for example 15 volts or more). Not all the modules need have a second function, and those that do may have quite different and unrelated functions.

Thus the modules on line 7 are addressed in turn, ending with module 6 and pulses X and Y. After the 7 millisecond interval following pulse Y, the voltage returns to zero briefly before the synchronising period for the next sequence starts and the measuring procedure for the modules is repeated.

The central control unit 2 initiates action only after it has noted, in two successive scans of the modules in line 7, an alarm condition existing in one or more of the modules; in this way, the incidence of false alarms can be significantly reduced.

The alarm modules in network 1 may be of any appropriate type and they may relate to any form of sensing as required: for example they may sense for flames or smoke, or for intruders, or they may sense for operational characteristics (e.g. voltage or current) of equipment to enable energy management of plant machinery. The alarm modules may be designed to provide a drawn current of any value between zero and approximately 20 mA, the size of current being an indication of the alarm condition of the module.Thus taking a smoke detector as an example: a drawn current of less than 4 mA could be ignored; and drawn current between 4 and 8 mA is recorded by the unit 2 in order that an engineer can be alerted to check the operation of the module, which might need some repairs or adjustment; a drawn current between 8 and 10 mA is recorded by the unit 2 as the detection of small quantities of smoke, of the order of that produced by a lit cigarette; a drawn current between 10 and 13 mA is recorded by the unit 2 as the detection of substantial quantities of smoke indicating the existence of a fire; and a drawn current above 13 mA is recorded by the unit 2 as the detection of dense smoke produced by an extensive fire.

The operation of central control unit 2 may be designed such that the second function of a given module is not utilized in every scan. Thus for example the unit 2 may only produce a pulse of 20 volts depth for module 4 in every third scan of line 7; alternatively or additionally the unit may produce a deepened pulse for module 4 when a specified event occurs in relation to one or more of the other modules.

In the network 1, the coaxial lines 8 and 9 forming transmission line 7 are used to provide the modules with power from central control unit 2.

The central control unit 2 may be operated such as to monitor a number of closed loops, each of the form as described above.

Figure 3 illustrates, in block diagram form, the primary features of an alarm module 30 for use in the network 1; Figure 4 illustrates the electrical circuitry which may be used in one such module.

The module 30 has a limited analogue capability in that, when addressed, the current drawn from the loop is directly proportional to the voltage at its input point W.

As described before, control unit 2 produces a sequence of pulses which are transmitted along the loop. Capacitors 31 and 32 in the module 30 maintain the voltages across the detector 33 and the module circuit, respectively, within acceptable limits while the line voltage is zero. The clock input of counter 34 is connected to the cathode of diode 35 via a resistor 36 such that the count advances every time the line voltage drops to zero. The outputs of counter 34 feed, both directly and via invertor 37, the AND gate 38. Selective use of invertors 37, resistors 39, and appropriate linking allows up to 32 distinct combinations of address identity to be set up. When the output of counter 34 corresponds to the address identity, AND gate 38 goes high enabling transistors 40, 41 and 42.The circuit arrangement is such that the current through the transistors is directly proportional to the voltage at the input which is itself connected to the sensing circuitry. Each module requires two pulses, of which the first clocks the counter forward but the module remains disabled allowing unit 2 to check the loop for changes before the second pulse checks the sensor.

Module 30 may also have a relay which is automatically operated to provide a line disconnection when a fault occurs in the line (e.g. a shortcircuit) between module 30 and the adjacent module. in this way the section of the line incorporating the fault is isolated but the remainder of the line can continue to operate. Preferably, in these circumstances the control unit 2 sends the pulse sequence down the line 7 in both directions.

Thus for example, each relay may be energised via the line 7, such that any line fault will cause an interruption in the power supply to an appropriate relay resulting in it becoming de-energised and disconnecting part of the line. Additionally or alternatively a relay may be operated by regular command signals from the central control unit.

Figures 5 to 7 relate to another form of installation embodying the present invention and distinguished from installation 1 primarily by incorporating a different module-addressing system. In this system, each module is assigned an unique 7-bit address code such that any module can be specifically addressed by the central control unit of the installation transmitting a signal incorporating the appropriate address code. Figure 7 shows schematically a suitable signal which has seven bits for an address code, two control bits, a parity bit, then a calibration section, a module-type identification section, and finally a module-condition section.The module-type identification section consists of a window which allows the module to transmit an analogue signal consisting of one of eight levels representing the type of module; the module-condition section consists of a window which allows the module to transmit an analogue signal whose value represents the condition of the module. After the central control unit has transmitted along the installation a signal as shown in Figure 7, the line voltage is increased for a short period to charge the capacitors in the modules.

This second form of installation has a number of features in common with installation 1, for example the use of the signal conductor to convey power to the module, the monitoring ofthe quiescent current in the conductor before the response is transmitted, and the transmission of the detector response is analogue form.

In this second form of installation, the addressing system is capable of operating on either a 2-wire circuit, (e.g. a common negative line and a signal line) from which the operating power for the modules and analogue sensors are derived, or a 4-wire circuit where two separate pair of wires are usef for carrying the signal and the power to the modules and high current devices such as active intruder detectors.

The system operates satisfactorily with open ended or spur wiring, optionally the main wiring spur (branch) being looped back to the control unit so that, in the event of a single line open circuitfault, all addressable points (i.e. these locations at which modules are positioned) are still monitored by the control unit.

Monitoring and protection against line short circuit can be achieved using strategically positioned isolation devices. Each addressing circuit is capable of accepting at least ten such devices. Removal from operation of a device connected to any addressable point does not disable the circuit beyond but must result in a fault being transmitted to the control equipment.

An alarm module can initiate an interrupt signal which is recognisable by the central unit at any time during the scan. This will enable the central control unit to produce a different and faster response under specific conditions, e.g. operation of manual emergency call modules of the "Break-Glass" variety.

A signal, as shown in Figure 7, consists of: (i) a reset period, not exceeding 10ms which is used to refresh energy storage capacitor(s) within the a sensorand/orthe associated addressable module; (ii) a digitally encoded signal, not exceeding 4ms, which contains a 7 bit address field and a 2 bit command field (iii)a wait period, not exceeding 2ms, which may be used by the receiving unit to monitor the residual condition on the line, i.e. quiescent current; (iv) a response period, not exceeding 4ms, which is used for transmitting two separate amplitude modulated signals being the respresentation of: a) the module type (at least 8 levels); b) the module condition (continuously variable).

In the case of a 2-wire addressing circuit, the line voltage is raised to a level greater than 22V but not exceeding 30V during the reset period. This voltage is derived from a source having an impedence of no more than 10 ohm, and is required to keep reservoir capacitors in the address units in a charged state.

Transmission of the address and command signals uses the self-clocking bi-phase encoded technique. There is no need to synchronise timing functions at the receiving and transmitting units.

Transmission of analogue signals is via amplitude modulation of the line current'voltage and covers the range 4to 20mA. The accuracy of the transmission is at least +0.5% of full range. This Figure includes the error introduced by any analogue to digital conversion carried out at the central control unit, but it also takes into account any corrections for continuous parasitic conditions inherent to the system such as quiescent currents.

The communication circuit in the central control unit and modules are designed to operate satisfactorily in the supply voltage range of 10 to 30V DC.

This is in order to enable applications in both intruder and fire systems which operate at 1 2V and 24V nominal respectively. In 12V systems the 4-wire circuit with separate signal and power supply lines are used.

Each module is designed so that, on decoding a valid address, it enables the sensor to respond by drawing current directly from the signal line corresponding to its type and then condition.

Each manual emergency-call module is designed so that, on decoding a valid address code, the status of a switch contact can be transmitted to the receiving unit as a fixed current level. A reference level corresponding to 1 out of 2 type of manual emergency-call module is also transmitted. The module is designed so that it shall be possible to connect several such manual emergency-call modules. In such a case it is possible to monitor the interconnection wiring for both open circuit and short circuit This may be achieved by using an E.O.L. resistor and transmitting, via the address unit, the corresponding current level to the receiving unit.

Provision can be made for a manual emergency call module to interrupt the addressing sequence causing an immediate response at the receiving unit.

This is via an optional link which enables the address unit to give a response for any address code received.

A line isolation unit continuously monitors the line voltage, and when detecting a short circuit it is capable of isolating the affected section whilst allowing the rest of the addressing circuit to function normally. In order to enable its use in a looped circuit the unit is capable of passing current in both directions. This line isolation unit detects the presence of a short circuit when it senses that the line voltage drops below 1V or the current rises above 1 00mA. The line isolation unit has a response time of at least 250ms, but not exceeding Is. The line isolation unit does not introduce a resistance in series with the line greater than 2 ohms, and does not draw more than 1 00uA from the signal line.

Claims (26)

1. An alarm monitoring installation comprising: a central control unit; a plurality of alarm modules connected to the central control unit along a common line; means to address each of the alarm modules in order to determine the condition of each alarm module; and means to effect measurement of the line characteristics during addressing of an alarm module.

2. An installation according to Claim 1, wherein the measurement means has means to effect measurement of the characteristics relating to the line alone, and measurement of the characteristics relating to the line and to the module together.

3. An installation according to Claim 1 or Claim 2, wherein the measurement means incorporates means to produce a signal formed of a sequence of pulses incorporating a number of pulses for each module, and each module has means to detect the appropriate pulses and to switch in sensing circuitry during the addressing operation of that module.

4. An installation according to Claim 3, wherein the signal-production means provides two pulses for each module, and the module has means to switch in the sensing circuitry upon detection of the second pulse.

5. An alarm module for use in an alarm monitoring installation according to any one of Claims 1 to 4, wherein the module has means to detect the appropriate pulses and means to switch in sensing circuitry during the addressing operation of that module.

6. An alarm module according to Claim 1,wherein the module has means to switch in the sensing circuitry upon detection of a second pulse.

7. A method for operating an alarm monitoring installation having a plurality of alarm modules connected to a central control unit via a common line, the method comprising: addressing each of the alarm modules in order to determine the condition of each module; and effecting measurement of the line characteristics during addressing of a module.

8. A method according to Claim 7, comprising: in addressing a module, measuring the characteristics relating to the line alone and then measuring the characteristics relating to the line and to the module together.

9. A method according to Claim 7 or Claim 8, comprising: producing a signal formed of a sequence of pulses incorporating a number of pulses for each module; each module detecting the appropri ate pulses and switching in the sensing circuitry during the addressing operation of that module.

10. A method according to Claim 9, comprising: providing two pulses for each module; a module switching in the sensing circuitry upon detection of the second pulse.

11. An alarm monitoring installation comprising: a central control unit; a plurality of alarm modules connected to the central control unit along a common line, each alarm module being assigned a specific detection function; means to address each of the modules in order to determine the condition of the module concerning the specific detection function; and means to command a module, during the addressing function, to perform an additional function.

12. An installation according to Claim 11, com prising: means, in the addressing means, to send a sequence of pulses along the common line; and means in a module, to detect the pulses appropriate to it and to determine any which command it to perform an additional function.

13. An installation according to Claim 11 or Claim 12, wherein the command means includes: means to produce pulses of different format to be standard pulses used in addressing the modules; and means, in the module(s), to distinguish the pulses of the command means from the standard addressing pulses.

14. An alarm module for use in an alarm monitoring installation according to any one of Claims 11 to 13, the module having means to effect, in normal operation, a specific detection function, and means to perform an additional function when so com manded.

15. An alarm module according to Claim 14, comprising means to detect the pulses appropriate to it and to determine any which command it to perform an additional function.

16. A method for operating an alarm monitoring installation having a plurality of alarm modules each having a specific detection function and connected to a central control unit via a common line, the method comprising: addressing each of the modules in order to determine the condition of the module concerning the specific detection function; and commanding a module, during the addressing step, to perform an additional function.

17. A method according to Claim 16, comprising, in the addressing step, sending a sequence of pulses along the common line; and a module detecting the pulses appropriate to it and determining any pulses which command itto perform an additional function.

18. A method according to Claim 16 or Claim 17, comprising, in the command step, producing pulses of different format to the standard pulses used in addressing the modules; and at least one of the modules distinguishing the command pulses from the standard addressing pulses.

19. An alarm monitoring installation comprising: a plurality of alarm modules connected to a central control unit along a common line; means to address each of the modules in order to determine the condition of the module; each of the modules having means to operate a relay to provide a line termination if a fault occurs in the common line between that module and the adjacent module downstream.

20. An installation according to Claim 19, comprising means to operate a relay in likewise manner on the other side of the fault.

21. An installation according to Claim 19 or Claim 20, wherein the central control unit also has means to send pulses down both sections of a common line when a fault occurs.

22. An alarm module for use in an alarm monitoring installation according to any one of Claims 19 to 21, the module having means to operate a relay to provide a line termination if a fault occurs in the common line adjacent to the module.

23. A method of operating an alarm monitoring installation having a plurality of alarm modules connected to a central control unit with a common line, the method comprising: addressing each of the modules in order to determine the condition of the module; and operating a relay, which provides a line termination, at a module adjacent a fault occurring in the common line.

24. A method according to Claim 23, comprising thereafter sending the pulses down both sections of the common line towards the fault.

25. An alarm monitoring installation substantially as hereinbefore described with reference to and as illustrated in Figures 1 to 4 or in Figures 5 to 7 of the accompanying drawings.

26. A method for operating an alarm monitoring installation substantially as hereinbefore described with reference to and as illustrated in the Figure 1 to 4 or Figures 5 of 7 of the accompanying drawings.