GB2237425A

GB2237425A - Surveillance system

Info

Publication number: GB2237425A
Application number: GB8922391A
Authority: GB
Inventors: Donald Stanley Clark
Original assignee: ZERO OPTION ELECTRONICS Ltd
Current assignee: ZERO OPTION ELECTRONICS Ltd
Priority date: 1989-10-04
Filing date: 1989-10-04
Publication date: 1991-05-01
Also published as: GB8922391D0

Abstract

A signalling system comprises a master unit 1 and one or more slave units 20 which can be polled cyclically by recognising a digital count value designating that slave unit, in which the master and slave units are interconnected by:- a. a polling channel 32, the digital count value being generated locally at each of the slave units by counting 22, during a polling cycle, a sequence of clock pulses on the polling channel, the pulses being counted 2,14 concurrently at the master unit; b. a synchronisation channel 28 for signalling between the units the start of each polling cycle; c. a signalling channel 30; and in which, an individual slave unit recognising that the digital count value designates that unit can cause the polling cycle to be temporarily paused. The pausing of the polling cycle at a particular point indicates a) the identity of the relevant slave unit and b) that a relevant status condition (eg, an alarm state) has been sensed by it. <IMAGE>

Description

SIGNALLING SYSTEM This invention relates to an electronic signalling system having particular, but not exclusive, application to surveillance and other status-monitoring systems.

A typical surveillance or status monitoring system comprises a master unit, usually associated with a control/status display channel and a number of slave units distributed around the premises or plant being monitored and wired to the master unit. Each slave unit may have one or more sensors associated with it to monitor an appropriate status condition, eg, intruder, fire or smoke detectors and is operative to signal the current status (or a change in status) back to the master unit, causing an appropriate status display to be activated. The system may provide for command signals to be tranttedback to the slave units, for example to sound an alarm, activate fire sprinklers and so forth.

The present invention relates to a system of the above type and seeks to reduce the complexities of wiring and circuitry which can arise where there is a significant number of slave units.

According to a first aspect of the present invention, there is provided a signalling system comprising a master unit and one or more slave units which can be polled cyclically by recognising a digital count value designating that slave unit, in which the master and slave units are interconnected by: a. a polling channel, the digital count value being generated locally at each of the slave units by counting, during a polling cycle, a sequence of clock pulses on the polling channel, a count of the pulses being maintained concurrently at the master unit; b. a synchronisation channel for signalling between the units the start of each polling cycle; c. at least one signalling channel; and in which, any individual slave unit, recognising that the digital count value designates that unit, can cause the polling cycle to be temporarily paused.

The method by which individual slave units are polled and the fact that the polling cycle is paused temporarily when a slave unit recognises that it is being polled both significantly contribute to a simple implementation of the system. By having the master unit and slave units count in step a sequence of clock pulses (conveniently generated at the master unit) the system avoids the need to transmit the address of the currently polled slave unit, so enabling a single wire to be used as the polling channel. The pausing of the polling cycle provides a simple means of providing at the master unit a read-out of the identity of the slave unit which has paused the cycle, since the master unit can simply display the current count of its polling counter, or use the count to look up and display a corresponding text message identifying the slave (or its location).The fact that a particular slave unit has paused the polling cycle can in itself be taken as a status indication that the slave unit is reporting on a status condition (eg, that an alarm has been tripped). Where in the cycle the pause occurs identifies the slave unit to the master unit. The pausing of the polling cycle enables the master unit to read further data from the slave unit (for example to read the temperature from a temperature sensor at the slave) or to send commands to the slave unit, eg, to initiate some action such as activating an alarm or requesting read out of further data from the slave unit.

A second aspect of the invention provides a master unit for use in a system according to the first aspect of the invention wherein the master unit comprises: a clock pulse generator for generating the clock pulses used during the polling cycle;, a counter for maintaining a count of the clock pulses; means for transmitting a reset pulse and the clock pulses to the slave units; means for receiving a stop pulse transmitted from one of the slave units via a shared stop-pulse channel forming part of the signalling channel; a display for displaying the identity of the slave unit originating a stop pulse by reference to the contents of the counter; and means for resetting the master unit counter and transmitting the reset pulses to the slave units.

A third aspect of the invention provides a slave unit for use in the system of the first aspect of the invention wherein the, or each, slave unit comprises: means for receiving the reset pulses and clock pulses, means defining an identification number for that slave unit; a counter for counting to the received clock pulse during a polling cycle; means for resetting the counter on receipt of a reset pulse; means for monitoring the contents of the counter to determine when the count indicates that that slave unit is being polled, and when that determination is in the affirmative to output a stop pulse via the signalling channel to the master unit if that slave unit requires to signal the master unit.

A number of the slave units may be daisy-chained together to connect them to the master unit using very simple wiring.

The present invention will be further described hereinafter with reference to the following description of an exemplary embodiment and the accompanying figure which shows a schematic diagram of an electronic surveillance system according to the present invention.

In figure 1, numeral 1 denotes the master unit generally and 20 denotes one of a number of slave units daisy-chained together by signal wires 28-34 and by two power supply wires (not shown).

The master unit 1 comprises a BCD (binary coded decimal) up counter 2 which increments by one unit each time a clock pulse is supplied, and which has its inputs 2a hard wired so that it returns to zero when reset. The outputs 2b of the up counter 2 are connected to the inputs 4a of a two digit display 4. Another output of the up counter is connected to the clock pulse generator and the reset pulse line 28 via an enable pulse shaper 8.

The display 4, when enabled by the display enable timer 12, displays the current value held in the up counter 2.

The display enable timer 12 is connected, via a buffer 41, to a stop pulse line 30, and, on detection of a stop pulse, enables the display 4 and an alarm 6 and sounder 7 for a short period of time whilst simultaneously pausing the clock pulse generator 10. The clock pulse generator 10 provides clock pulses to the up counter 2, the clock pulse line 32 and a BCD down counter 14.

The reset input of the down counter 14 is connected to the reset pulse line 28. The inputs of the alarm counter 14 are connected to an array of switches 16 on which a slave identification number is set in binary. The output of the down counter 14 is provided to the slave enable pulse line 34.

The system may include up to 99 slave units 20 connected in parallel to the reset pulse line 28, stop pulse line 30, clock pulse line 32 and slave enable pulse line 34.

Each slave unit 20 has a BCD down counter 22 the inputs of which are connected to an array of switches 24 on which a two-digit BCD number identifying the slave is set.

When the down counter 22 reaches zero its output goes high opening AND gates 25 and 27. AND gate 27 then takes on the state of R-S flip-flop 26 and a pulse is put onto the stop pulse line 30 if the flip-flop 26 is in an alarm condition.

When the AND gate 27 is opened this allows a pulse, if there is one, from the slave enable line through to a device attached to the slave unit. The reset input of the down counter 22 is connected to the reset pulse line 28.

The functioning of the system will now be explained.

On starting a cycle the master unit issues a reset pulse setting the up counter 2 to zero and the down counters 22 in the slave units to their respective identifying numbers.

The clock pulse generator is then enabled and generates a clock pulse. This clock pulse causes the up counter 2 to increment so that it now holds the value 1, and all the down counters 22 to decrement so that the down counter in the nth slave unit holds the value n-l. The down counter in the first slave unit (n=l) will now be holding the value zero so its output will go high opening gate 25.

The status of the monitoring device attached to the slave unit is stored in the flip-flop 26. If this is high, ie, in an alarm condition, then when gate 25 is opened by the output of the down counter 22 the stop pulse line 30 will also go high. When the stop pulse line 28 goes high the display enable timer 12 disables the clock pulse generator 10 and enables the display 4 which displays the contents of the up counter 2. This will be "l" thus clearly indicating to the user that slave unit no. 1 is in an alarm condition.

The display enable timer 12 also triggers the alarm 6 connected to the sounder 7. After a predetermined period of time, eg, a few seconds, the display enable timer disables the display 4 and enables the clock pulse generator 10.

This then generates another clock pulse which increments the up counter 2 and decrements all the down counters 22. After 99 counts the system resets and starts again from zero.

After k clock pulses the up counter 2 will have the value k while the down counter in the kth slave unit will be at zero. Thus if the kth slave unit is in an alarm condition the count is paused and the display shows the number k indicating where the alarm is. If the kth slave unit is still in an alarm condition when the count recycles to k again this is again indicated.

The zero count outputs of the down counters 22 are also connected to their respective enable inputs. When a down counter reaches zero the high output disables the down counter until it is reset when the up count reaches 99.

Since each slave unit is given a unique number only one down counter will reach zero at any one time hence it is possible to use only one signalling channel or line while still being able to identify which unit is signalling.

If several slave units are in an alarm condition their numbers will be displayed cyclically until the alarm conditions are cleared.

When an alarm condition is cleared the flip-flop in the slave unit may be reset locally by a push button or all the flip-flops may be reset at once by depriving the units of power or via a separate reset line.

If no alarms are detected the polling cycle takes about a second. This can be varied according to the response speed of the various components in the master and slave units.

In this embodiment the master control unit is also provided with a BCD down counter 14 and a set of switches or keypad 16 on which a BCD slave identification number can be set. This down counter is provided with clock pulses and counts down as the down counters 22 in the slave unit. If the switches 16 are set to a number n then the down counter 14 will reach zero at the same time as the down counter 22 in the nth slave unit. Down counter 14 will then put a slave enable pulse onto the slave enable number line 34.

Since only the gate 27 in the lth slave unit 20 will be open at this time the slave enable will be passed to only a device attached to the nth slave unit. Thus by setting the appropriate number on the switches 16 a user can send an enabling pulse to a particular one of the remote devices attached to a slave unit. This might be a test pulse or reset pulse or might trigger the device to send data back in return. In the latter case the device trigger might, for example, set an alarm condition on the flip-flop 26 so that the display enable timer 12 halts the count and then put data onto the stop pulse line by-passing the flip-flop 26 and AND gate 25. This data can then be intercepted from the stop pulse line in advance of the display enable timer by the data decoder 18.Information can be passed selectively to the remote devices in a similar manner along the slave enable pulse line 34, eg, to reset the slave unit or to initiate some other command such as to trigger an alarm local to the slave unit.

Since the clock, reset and stop pulses are available at all points on the cabling extra pseudo "master", ie, display units may be provided at any point.

An extra display unit would comprise an up counter with its inputs hard wired to zero and its outputs connected to a display. The clock input up counter is provided with clock pulses from the clock pulse line 32 while the reset pulse line 28 is connected to the reset input. The stop pulse line is connected to the display enable input on the display so that the display shows the contents of the up counter when the stop pulse line goes high. Since the extra display unit uses the lock pulses provided by the master unit it is synchronised to the master and will always display the same number.

One possible application for the system is as a lift indicator. A master unit is provided at one floor, for example the ground floor, and a slave unit and extra display unit at each other floor. Each slave unit is triggered into an alarm condition by the presence of the lift at its floor and are arranged so as to reset when the lift has left the floor. The slave units could be triggered by reed or micro switches and arranged to reset by an R-C circuit with an appropriate time constant . Since the likely number of floors, and therefore slave units, is small, the polling cycle will be much faster then the lift and the master and extra display units will display the floor number as the lift passes each slave unit. If the lift is stationary at a floor then the automatic reset will be disabled and the floor number will flash or blink as the alarm condition is repeatedly detected.A display unit could also be provided in the lift via a track or coiling conductor. This system has the advantage that the failure of any of the slave or display units affects only that unit and the remainder of the system will continue to function normally.

Power may be provided to the slave units on a conductor or may be provided locally, eg, by batteries.

Other communications methods such as: filter optics, radio, infra-red, ultra-violet, etc, may be used with appropriate transducers.

The described embodiment is usable with up to 99 slave units because of the provision of only a two digit display and two digit BCD counters. Obviously, a greater or smaller number of slave units could be catered for by varying the number of BCD digits.

The use of simple switches, DIP switches being particularly suitable, to set the identification number of the slave units allows these units to be interchangeable and cheap to produce; however any suitable method may be used.

The system does not require any reprogramming or adjustment if the number of slave units connected, within the maximum, is varied. This also makes installation, and later modifications, of the system easy.

In the above described embodiment, four separate wires 28-34 are used for the three sending and one receive channels from the master to the slave unit. It will be appreciated that these four wires could be replaced by a two-wire pair, with the various signals being time-division multiplexed together, at the expense of requiring somewhat more complex circuitry at the master and slave units to handle the multiplexing and demultiplexing of the signals.

Claims

1. A signalling system comprising a master unit and one or more slave units which can be polled cyclically by recognising a digital count value designating that slave unit, in which the master and slave units are interconnected by: a. a polling channel, the digital count value being generated locally at each of the slave units by counting, during a polling cycle, a sequence of clock pulses on the polling channel, a count of the pulses being maintained concurrently at the master unit; b. a synchronisation channel for signalling between the units at the start of each polling cycle; c. at least one signalling channel; and in which, any individual slave unit, recognising that the digital count value designates that unit, can cause the polling cycle to be temporarily paused.

2. A system according to claim 1 wherein the master unit is operative, while the polling cycle is paused, to indicate the identity of the slave unit for which the cycle is paused.

3. A system according to claim 1 or 2 in which the master unit effects the clocking of the polling channel and the pausing of polling in response.

4. A system according to claim 1, 2 or 3 in which whether or not the polling cycle is paused, following recognition by a slave unit that the poll count designates that unit, depends on a status signal associated with the slave unit.

5. A system according to any one of claims 1 to 4 wherein, while the polling cycle is paused, status data is transmitted from the slave unit which caused the pause to the master unit and/or command data is transmitted to that slave unit from the master unit.

6. A system according to any one of the preceding claims, wherein the master unit comprises: a clock pulse generator for generating the clock pulses used during the polling cycle;, a counter responsible for counting the clock pulses; means for transmitting a reset pulse and the clock pulses to the slave units; means for receiving a stop pulse transmitted from one of the slave units via a shared stop-pulse channel forming part of the signalling channel; a display for displaying the identity of the slave unit originating a stop pulse by reference to the contents of the counter; and means for resetting the master unit counter and transmitting the reset pulses to the slave units.

7. A system according to any one of the preceding claims, wherein the, or each, slave unit comprises: means for receiving the reset pulses and clock pulses, means defining an identification number for that slave unit; a counter for counting to the received clock pulse during a polling cycle; means for resetting the counter on receipt of a reset pulse; means for monitoring the contents of the counter to determine when the count indicates that that slave unit is being polled, and when that determination is in the affirmative to output a stop pulse via the signalling channel to the master unit if that slave unit requires to signal the master unit.

8. A system according to claim 6 wherein the display means includes display timer means adapted to pause the clock pulse generator for a predetermined period upon receipt of a stop pulse during which period the display means displays said contents of the counter.

9. A system according to claim 6 or 7 wherein said display means further includes alarm means for signalling an alarm condition on receipt of a stop pulse.

10. A system according to claim 6, 7 or 8 wherein said master unit further comprises slave unit enabling means comprising a second counter which clocked by the clock pulses, slave number setting means for setting the number of a slave unit to be enabled, wherein said second counter is set to the number designating a slave unit to be enabled and generates a slave unit enable pulse to the slave units when the second counter contents corresponds to the number of the designated slave unit.

11. A system according to claim 7 or claim 8 or 9 when appendant thereto wherein said slave unit further comprises an enable gate which opens when the contents of the slave unit counter indicates that that slave unit is being polled to allow a slave enable pulse to be provided to said slave unit and/or a device attached thereto.

12. A system according to any one of claims 1 to 10 wherein the master and one or more slave units are interconnected by a reset pulse line, a stop pulse line and a clock line, the reset pulse line and stop pulse line constituting the signalling channel.

13. For use in a system according to any one of claims 1-12, a master unit comprising a clock pulse generator for generating the clock pulses used during the polling cycle;, a counter for maintaining a count of the clock pulses; means for transmitting a reset pulse and the clock pulses to the slave units; means for receiving a stop pulse transmitted from one of the slave units via a shared stop-pulse channel; a display for displaying the identity of the slave unit originating a stop pulse by reference to the contents of the counter; and means for resetting the master unit counter and transmitting the reset pulses to the slave units.

14. For use in a system according to any one of claims 1 to 12, a slave unit comprising means for receiving the reset pulses and clock pulses, means defining an identification number for that slave unit; a counter for counting to the received clock pulse during a polling cycle; means for resetting the counter on receipt of a reset pulse; means for monitoring the contents of the counter to determine when the count indicates that that slave unit is being polled, and when that determination is in the affirmative to output a stop pulse to the master unit if that slave unit requires to signal the master unit.

15. An electronic surveillance system constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

16. A master control unit for use in an electronic surveillance system, constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

17. A slave unit for use in an electronic surveillance system constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.