GB2061583A - Self-priming interlock/warning system - Google Patents

Abstract

The output of an interlock/warning system can be inhibited so that an abnormal condition can be permitted to exist without an interlock/warning output being generated. Once a condition of normality has returned and remains in existence for a predetermined period of time (timer A) the "Inhibit" is removed automatically from the output so that any subsequent abnormal condition will give rise to an interlock/warning output. An abnormal condition can be rendered ineffective within (say) 7 seconds of its existence (timer B) by the application of a "cancel" signal. Failure to apply a "cancel" signal (within the 7 second period) once an abnormal condition occurs will result in an interlock/warning output being generated for a predetermined period (timer C). One application is that of a vehicle alarm - where the use of seat switches enables the abnormal (occupied) condition to exist without sounding a warning once a cancel signal has been applied. Once the vehicle is left unattended with doors/bonnet/boot closed (normal condition) for in excess of a predetermined time period, the inhibit is automatically removed from the output so that any subsequent abnormal condition (door opening, etc) will give rise to warning output (horn, ignition immobilise). <IMAGE>

Description

SPECIFICATION A self-priming interlock/warning system The invention relates to a timing/interlock device by which the presence of an input stimulus prevents an alarm" output being generated. The absence of an input stimulus for a period in excess of a predetermined time period causes the function of the input stimuli to be inverted so that the presence of an input stimuli will now initiate a cycle which will eventually generate an "alarm" output(s). A facility is provided to re-invert the function of the input stimuli during a particular phase in the forementioned cycle so that the stimulus which initiated the cycle (or any other stimuli) will again serve to prevent the "alarm" output being generated.This re-invertion is brought about by the application of a signal on a "cancel input", and a "cancel" output signal is generated indicating this particular phase in the cycle. A facility is provided so that momentary application of input stimuli will initiate the forementioned cycle. A facility is provided so that (in the absence of an input stimuli) the cycle will progress to a particular phase during which the "alarm" output will cease to be generated. Thus the cycle will have progressed through 360 and the circuit is ready to be retriggered by the appearance of an input stimuli and the cycle will repeat itself. A facility is provided to arrest the cycle in the "alarm" output phase by the presence, and for the duration of any input stimuli.In addition the cycle will remain in that particular phase for a predetermined period after the arresting input stimuli had been removed.

The terms "alarm" and "cancel" have been used only to aid description. These outputs/inputs can, of course, feed or be derived from any apparatus.

The invention has particular though not exclusive application in alarms, warnings, and security protection systems.

A particular application envisaged for the invention is in processing output signals from security detectors mounted in on or around a vehicle so as to make up a security system which becomes "active" when all detector outputs have been absent for a predetermined time period.

By feeding the alarm output to the horn or siren and by feeding other alarm outputs to the ignition contact breaker the horn could be arranged to sound and the ignition immobilised when a detector output is generated after the system had become active. An audible, visual, or sensual device connected to the cancel output would give an indication that the alarm cycle was in a phase that could cause the input function to be re-inverted by applying a signal to the cancel input. This signal from either a security key operated self-cancelling switch or by a concealed self-cancelling switch or push button would provide the owner or other authorised person with a means of entering the vehicle without the horn or siren sounding.

Some of the advantages of using the invention in the vehicle alarm configuration as outlined above are as follows: 1. The device is self priming and therefore does not have to be switched on. The presence of the driver causes the detectors to produce outputs which will prevent the alarm output being generated. Absence of the detector output signals indicate the driver has left the vehicle-and if these outputs are absent for longer than the preset time period the input function inverts.

2. A potential thief has only a limited time (which can be made to be very short) to locate the concealed cancel switch or to by-pass or otherwise overcome the security key lock before the horn sounds. Operating the cancel input after that phase of the alarm cycle has passed is ineffective.

3. The alarm will sound for the period that the detector output remains.

4. The alarm will reset by itself after a fixed time period has elapsed. Thus economising on battery current and causing less annoyance to neighbours.

5. The alarm resets into the active state so that subsequent attempted entry will be detected and the alarm sounded.

6. It causes a minimum inconvenience to the driver who must only operate the cancel input when the cancel output is active.

7. The driver can move around the outside of the vehicle always providing that the periods between each operation of the detectors is less than the predetermined time period, set for invertion of the inputs to take place.

By way of example only the following is a description of a typical vehicle alarm system using the invention as a processing unit for the detector signals. A block diagram of this use is shown in Fig. 1. In this instance a seat switch is fitted under the driver's seat so as to provide an O-volt output when the driver is present. Other inputs are derived from the courtesy light switches mounted in each door, from switches mounted so as to give an O-volt output when either boot or bonnet are opened, and from inertia switches (via their own converter logic boxes) mounted in the door frame.

Once the driver has entered the vehicle and operated the cancel input, the seat switch (which provides a O-volt output when the seat is occupied) will maintain an input to the invention thus preventing the inverting function taking place for as long as the seat is occupied.

Alternatively any door or bonnet or boot being opened or any output from the inertia switches will (once the cancel input has been operated) reset the internal timer providing they occur within the preset timing period.

The use of a seat switch has the advantage that as soon as the driver gets out of the vehicle the preset time period begins to expire-then it is reset by the door output. Now once the door is closed the preset period again begins to expire and providing no further detector outputs are presented to the Invention inputs within the preset time period the invertion of the input function will take place. [The further advantage of the seat switch is that it prevents invertion taking place while the driver is seated in the vehicle thus eliminating the necessity to operate the cancel input as the driver leaves the vehicle (having supplied a detector output by opening the door).

A further advantage of the seat switch is that it will produce an output which when fed into the invention input will arrest the alarm cycle in the "alarm output generate phase.] An output subsequently generated by any of the detector circuits will initiate the alarm cycle which can only be reset by applying an O-volt signal to the cancel input within a predetermined time, (while the cycle is in a particular phase).

An audio and or visual device attached to the cancel output will serve to remind the driver to apply the cancel input (which may be done by means of a concealed spring loaded switch or a hidden internal security switch).

If the cancel input is not applied within the prescribed phase of the alarm cycle the alarm outputs will be generated causing the horn to blow and the ignition to be immobilised. The alarm cycle will be arrested in this phase until all detector outputs have been removed for a predetermined period. Then the alarm cycle progresses. Thus having cycled through 360" the alarm cycle will be again initiated by any subsequent detector outputs applied to the invention's inputs.

The above mentioned inputs have been stated as O-volts by way of illustration only. Simple electrical invertors connected prior to these inputs will cause the inputs to be operated by positive signals. Further the inputs can be made to operate on negative signals by using a suitable interface circuit prior to the inputs.

Features and advantages of the invention will become apparent from the following description, given with reference to the drawing (Fig. 2) which is a schematic circuit diagram of an embodiment of the invention.

The apparatus illustrated in the drawing includes an input isolator circuit (11) which prevents the input signal on any input line (12, 13, 14, 15, 16,) from feeding back out on any other input line. An input appearing on any input line (of which there may be any convenient number) will develop a signal on line 17. The signal on line 17 is fed to an "and function gating device" 18, and to "and function gating device" 24.

Sufficient time having elapsed from a previous operation, time delay device 25 produces a sustained enable signal on line 21. The signal on line 21 is inverted by invertor device 28 and fed by line 27 to "and function gating device" 1 8. The signal on line 27 inhibits the signal on line 17 from passing through "and function gating device" 1 8 and so the signal on line 17 is prevented from appearing on line 35.

The presence of signals on lines 21 and 17 causes "and function gating device" 24 to produce an output on line 26.

The output on line 26 is fed to time delay device 29, to memory device 19, and to time delay device 40. The signal on line 26 causes memory device 19 to produce an immediate sustained output on line 22. The signal -on line 26 has no effect on timer delay device 40 as that device has not been started at this stage of the circuit's operation. The signal on line 26 starts time delay device 29 to time out.

The output from memory device 1 9 is fed on line 22 to an "and function gating device" 23 and a output driver device 20. The signal on line 22 causes output driver device 20 to produce a convenient electrical output referred to as the cancel output. The signal on line 22 causes "and function gating device" 23 to pass any signal appearing on line 30 on to line 31.

A signal appearing on the cancel input line 30, during the period that "and function gating device" 23 is enabled by reason of the signal on line 22, is fed on line 31 to time delay device 25, to "or function gating device" 39, and to "or function gating device" 32. A signal on line 31 causes "or function gating device" 39 to produce a signal on line 38. A signal on line 38 resets time delay device 29 and thus no output is produced on line 34. A signal on line 31 causes "or function gating device" 32 to produce an output on line 33. A signal on line 31 restarts time delay device 25. While timing out, time delay device 25 causes a disable signal to appear on line 21; thus "and function gating device" 24 is inhibited, so that signals appearing on line 1 7 cannot be passed on to line 26.

The disable signal on line 21 is inverted by invertor device 28 to produce an enable signal on line 27. The enable signal appearing on line 27 is fed to "and function gating device" 18, which in turn allows the signal appearing on line 1 7 to be passes on to line 35. A signal appearing on line 35 is fed to time delay device 25; and has the effect of overriding the lapsed time circuit and restarting the timing period again, (thus providing a means of extending the timing period of time delay device 25 indefinately).

A signal appearing on line 33 erases memory device 19, thus no signal appears on line 22.

This in turn causes "and function gating device" 23 to be disabled and also causes cancel output driver 20 to cease producing an output.

The circuit remains in this state with "and function gating device" 24 disabled and with "and function gating device" 1 8 enabled until time delay device 25 times out. As time delay device 25 is continually restarted by the presence of signals on input lines 12, 13, 14, 15, and 16, (which are fed via input isolator 17, and via "and function gating device" 18,) time delay device 25 will only begin to time out when all input signals on the above input lines are removed. The reappearance of any signal on input lines 12, 13, 14, 15, or 16, will immediately restart the time delay device 25 providing that it occurs before time delay device 25 has timed out completely.

When time delay device 25 has timed out completely it produces a sustained enable signal on line 21, which enables "and function gating device" 24, and (By reason of invertor device 28), produces a disable signal on line 27, thus disabling "and function gating device" 18.

Subsequent inputs fed to produce signals on line 1 7 are passed via "and function gating device" 24 to line 26, thereby causing memory device 1 9 to produce an immediate sustained output on line 22 and causing time delay device 29 to start to time out, as described earlier in this document.

If time delay device 29 is allowed to time out (that is, if no cancel input is applied while the time delay device is in the process of timing out), it produces a sustained signal on line 34 at the end of the time period. The signal on line 34 is applied to "or function gating device" 32, to time delay device 40, and to alarm output driver device 35. The signal on line 34 causes time delay device 40 to start to time out. The signal on line 34 causes alarm output driver device 35 to produce convenient electrical signals on alarm output lines 37. The signal on line 34 will cause "or function gating device" 22 to produce a signal on line 33. As already described the signal on line 33 erases memory device 1 9 thus removing the signal on line 22.

As a result of the enable signal on line 21, described earlier, any signal appearing on lines 12, 13, 14, 15, or 16, is fed to line 26 during this phase of the invention's operation. A signal appearing on line 26 overrides the lapsed time circuitry of time delay device 40, thus returning the timer to start. In this way the time delay device 40 can produce an indefinately extended time.

At the end of the timing period, time delay device 40 produces a pulse signal on line 36. Line 36 feeds alarm output driver device 35, and "or function gating device" 39. The signal on line 36 causes alarm output driver device 35 to cease producing an output signal on lines 37. The signal on line 36 causes "or function gating device" 39 to produce a signal on line 38. The signal on line 38 resets time delay device 29 thus removing the sustained signal present on line 34.

The invention has now completed its cycle referred to as the alarm cycle. A further input presented to any of the input lines 12, 13, 14, 15, or 16, will be fed to line 26 and reinitate the alarm cycle.

Time delay devices 25, 29 and 40 may be a single timer with its inputs and outputs gated to perform the three timing functions.

The time delay devices may be arranged to time for any convenient period. Convenient time delays for vehicle security purposes may be as follows: Time delay device 25 1 minute Time delay device 29 7 seconds Time delay device 30 40 seconds In the case where the invention forms part of a vehicle security system a further output could be taken from line 31 and fed by way of a suitable driver device stage to produce a convenient electrical output to operate a electromechanical device for locking the bonnet of the vehicle closed, thereby preventing ready access to the vehicle electrics, horn and the invention itself.

By way of example only the following is a description of a convenient electronic circuit shown in Fig. 3 which may be used to process data in a vehicle security system.

Detector inputs shown, pins 5, 6, 7, 8, are those which respond to O-volt input signals.

Diodes D1, D2, D3, and D4, provide signal isolation to prevent an O-volt signal presented to one input appearing in the form of an output on any other input line.

To aid explanation of the circuit's operation, assume that sufficient time has elapsed to allow relay RL1 to re-energise.

An O-volt input appearing on any input (pin 5, 6, 7, or 8,) is fed via an input diode, and RLl /1 to the emitter to T2 causing transistor T2 to be biased into conducting by current fed through resistors R6 and R7. Current through the collector of T2 causes relay RL2 to energise.

Relay RL2 energising causes contacts RL2/1, RL2/2, RL2/3, and RL2/4 to change over. Thus a latching circuit is provided via contact RL2/1 to the emitter of T2. Contacts RL2/3 and RL2/4 provide switching between output pins 1 8 and 13, and between output pins 1 9 and 17, so any convenient electrical signal fed on to pin 1 3 will appear on pin 18, so either pin 1 8 or 1 9 can be used as "cancel" outputs. Similarly any convenient electrical signal fed on to pin 1 7 will appear on pin 1 9. Contact RL2/2 changing over causes capacitor C1 to charge via D6, R3, and R4.

An O-volt cancel input applied to pin 3 at this stage in the operational cycle removes the drive current to the base of T2 by providing a short circuit path to O-volts via relay contacts RL1 /2.

As the result of having the drive current removed transistor T2 ceases to conduct thereby causing RL2 to de-energise. Relay RL2 de-energising causes contacts RL2/1, RL2/2, RL2/3, and RL2/4 to return to the rest condition.

When contacts RL2/3 and RL2/4 return to the rest condition, they remove the electrical path between output pins 13 and 18, and between output pins 17 and 19. Thus providing a means of removing the cancel output once the cancel input has been operated.

When contacts RL2/2 returns to the rest condition it provides an electrical path from pin 3 (which is still at O-volts due to the presence of the cancel input) to R2. Thus C1 rapidly charges via D6, R2, RL2/2, and RLl /2. As the voltage across capacitor C1 increases so too does the voltage across the coil of RL1, (by emitter follower action of transistor T1).

As relay RL1 begins to energise the contacts RL1 /2 begin to open circuit. This removes the O-volt charging path to C1, but due to the charge held in C1, and due to the relay pole pieces coming closer together, the relay changes over. Any O-volt input present on any detector input (pins 5, 6, 7, 8) now holds relay RL1 energised via its own contact RL1/1, and charges capacitor C1 by way of diode D5 and R5.

Note: The circuit is arranged so that it operates in the above described sequence when the cancel input is operated (i.e. RL2 de-energises then RL1 energises). In this way the alarm state (i.e. RL1 and RL2 energised at the same time) is avoided. If the circuit operated differently then the horn would sound briefly each time the cancel output demand was acknowledged by the cancel input being operated.

The invention remains in this state for a preset period of time after all detector inputs are removed. This time period is determined broadly by the value of C1, the dropout voltage of RL1, the leakage of current via T2, C1, D6, D5, and R1, and the gain of T1.

An input occurring on pins 5, 6, 7, or 8 before RL1 has de-energised "tops-up" the charge in capacitor C1 (via D5 and R5) and thus effectively restarts the time period of the circuit.

If sufficient time is allowed to elapse so that RL1 has de-energised, and an input is subsequently applied to pins 5, 6, 7, or 8 it causes RL2 to energise as already described. Thus the alarm cycle is initiated.

When RL2 energises C1 begins to charge via D6, R2, R3, and R4 as already described. If the cancel input pin 3 is not operated during this phase of the alarm cycle, then the voltage across C1 will increase thereby energising RL1 as already described.

Relay RL1 energising causes contacts RLl /1, RL1 /2, RLl /3, and RL1 /4, to change over.

The circuit is now in the alarm state, (i.e. Both relays are energised simultaneously). Contacts RLl /3, together with contacts RL2/3 provide an electrical path between output pins 10 and 13. Thus a convenient electrical signal applied to pin 1 3 appears on pin 10 during this part of the alarm cycle. Similarly a signal applied to pin 1 7 appears on pin 14 via contacts RL1 /4 and RL2A4.

Any input present on the pins 5, 6, 7, or 8, holds relay RL1 energised and "tops-up" the charge in C1 as already described. Thus the alarm cycle is arrested in the alarm phase.

Contact RLl /2 changing over disconnects the cancel input and provides an electrical path for current flowing from the positive supply rail via R6 to R4. This current flowing through R4 to 0volts develops a voltage across R4 of approximately 11 volts, (depending on the values of R6 and R4 and the DC supply voltage).

If no inputs are present on pins 5, 6, 7, or 8, then the capacitor C1 begins to discharge when contact RLl /2, make, as the positive voltage developed across R4 prevents C1 charging further to the O-volt line. The diode D6 is back biased at this point so that C1 can not discharge via R2.

When the voltage across C1 has dropped to a particular level, RL1 will de-energise. The voltage across R4 will fall from (say) 11 volts 0 volts. This voltage drop is fed via C2 so as to produce a negative voltage pulse of (say) - 10.5 at the base of T2. Transistor T2 is this switched off causing RL2 to de-energise and remain de-energised through opening the latching contact RL2/1. The alarm cycle has passed through 360 and is now ready to be initated again by any appearance of a detector pulse fed to pins 5, 6, 7, or 8.

Note: If for any reason the negative pulse fed to the base of T2 fails to turn off T2 then the charge/discharge cycle of C1 repeats itself and thus another negative pulse is generated to turn T2 off.

C3 prevents instability. D7 and D8 are diodes used to clip the reverse EMF generated by relays RL1 and RL2 de-energising.

The circuit has the following distinctive states of operation: Relay 1 Relay 2 1 0 Input stimulus present. Cancel input operated.

0 O "Armed" state 0 1 Cancel phase 1 1 Alarm phase 1 = Energised O = De-energised This type of circuit has many advantages, some of which are listed below: 1. From the above table it can be seen that when the circuit is "armed" (i.e. sufficient time has elapsed since the last detector stimulus to allow relay RL1 to de-energise), very little current is needed to maintain it in this state of readiness. The only current being leakage through C2 and T1.

2. A similar circuit may be constructed for use with a negative supply by transposing the transistors (i.e. making T1 a PNP type and T2 a NPN type) and changing the polarity of the diodes and C1.

3. The inputs are low impedance level triggered, thus: (i) are not susceptable to false triggering by electrical interference.

(ii) give reliable operation even when stimulated by input signals with very low speed rising edges which may occur on corroded switch contacts.

4. All inputs which serve to drive the circuit into an alarm cycle, can also be used (by operating the cancel input) to prevent the circuit becoming "armed".

5. The circuit ceases to generate an alarm output a fixed period of time after the last detector input stimulus has been removed, and returns to the armed state, ready to detect any subsequent attempts at entry.

6. The cancel input must be operated within a fixed period (i.e. the cancel phase of the alarm cycle) otherwise it is disconnected.

7. All inputs are tripped by O-volts thus additional sensors can be provided by the electrical circuits already fitted to the vehicle (i.e. brake lamp circuit, or windscreen wiper circuit).

Similarly the cancel input can be connected so as to be operated by already existing electrical switching in the vehicle. This makes discovery of the cancel switch even more difficult for an intruder to locate. A circuit by way of example is shown below in Fig. 4.

More than one cancel switch may be wired in series to make the cancel input more difficult for an intruder to locate by chance. A circuit by way of example is shown below in Fig. 5.

8. A simple interface circuit placed before any input can invert or alter the character, of that input so that it is triggered by a positive voltage or a negative voltage or by a fast rising edge or a falling edge or by any other type of electrical stimulus.

9. Upon installation (or after temporary removal of the power supply,) the circuit enters the armed mode immediately the power is restored.

10. Momentary input signals initiate the alarm cycle if the circuit is in the armed mode.

11. Very little current is drawn by the circuit while in the armed state.

1 2. The cancel input functions regardless of the presence or absence of stimuli on the detector inputs.

1 3. Output alarm circuit contacts are of the self-cleaning type. All electromechanical devices are operated each time the alarm cycle is initiated. Thus reducing the possibility of alarm failure due to corroded contacts or seized electromechanical devices.

1 4. The input stimulus may be from seat switches under vehicle driver and passenger seats; so that the presence of a person in either seat prevents the circuit going into the armed state.

1 5. The inputs can be fed from door switches, inertia switches, pressure pads, pendulum switches, mercury switches, ultrasonic detectors, radar detectors, sonar detectors and other types of detectors.

16. The cancel output may be fed to a device which locks the bonnet of the vehicle closed when a cancel output is present. Suitable gating can be introduced so that the bonnet can only be unlocked by operation of the cancel button during the cancel phase of the alarm cycle. Thus preventing access to the alarm circuitry wiring of the vehicle.

1 7. The circuit may be used to process electrical signals generated from sources other than personnel detectors; for example, the circuit may be used to provide a temporary override of an alarm signal without running the risk of the possible human error of forgetting to remove the override device.

18. The circuit may be used for automatic pump priming, and other industrial uses.

1 9. The device may be used in the military field as weapons control and safety devices.

20. The device may be used in security systems for buildings or structures constructed on above or below the surface of the earth. Examples of such uses are dwellings, museums, art galleries, factories, safe deposits or vaults.

The device may be constructed so as perfrom the functions already described, by various means other than those given by way of example, e.g. the invention may be constructed so as to carry out the function by means of hydraulics, mechanics, electrics, fluidics, pneumatics, chemical action or other means.

The device may be constructed to perform the function described above by use of integrated circuits, single chip devices, field effect transistor devices, thermionic valves or other electric/ electronic components.

PRIOR ART Hitherto separate bypass, override, or on/off switches have been relied upon to suspend survillance so as to prevent an interlock or alarm output being generated by one or more of the monitored parameters exceeding its predetermined limit it was necessary to reset such bypass, override or on/off switch (or rely on a timer or some other device to do so) when surveillance of the above parameters was to be resumed.

The invention uses a momentary application of a "suspend" or "cancel" signal together with all or some of the monitored parameters to inhibit the alarm/interlock outputs so that surveillance is suspended until all of the parameters selected have ceased to exceed their predetermined limits for a fixed time period, then surveillance is automatically resumed.

Thus outputs due to abnormal conditions which are deliberately inhibited by an application of a "suspend" or "cancel" signal will remain so inhibited until a condition of normality exists for a predetermined time limit-then the inhibit is automatically removed.

Claims (6)

1. A self-priming interlock/warning device which has one or more inputs of a group which for convenience are referred to as "cancel" inputs and one or more inputs of a group which for convenience are referred to as "sense" inputs and one or more outputs of a group which for convenience are referred to as "warning" outputs and one or more outputs of a group which for convenience are referred to as "cancel" outputs.

The device has four separate modes of operation which for convenience are referred to as Phase 1, Phase 2, Phase 3, and Phase 4 respectively.

The device operates by transferring between the different modes of operation, dependant upon the stimuli presented to the inputs. The sequence in which such stimuli are applied and lapsed time between different stimuli. In this way the device processes stimuli which are presented to the input groups and generates a signal on the outputs in certain cases as described below.

Description of Modes Phase 1. In this phase, stimuli on one or more of the sense inputs prevent a signal being generated on the warning outputs.

Phase 2. In this phase no input stimuli are being processed and no signals are being generated on the warning outputs.

Phase 3. (Applicable to Claims 2, 3, 4, 5, and 6 only.) In this phase the presence for any length of time of a stimulus on one or more of the cancel inputs causes the device to transfer to phase 1 operating mode.

Phase 4. In this phase a signal is generated on the warning outputs.

A stimulus presented to one or more of the sense inputs during phase 2 mode of operation causes the device to transfer to Phase 4. mode of operation.

A stimulus presented to one or more of the cancel inputs during phase 2 mode causes the device to transfer to Phase 1 mode of operation.

A stimulus presented to one or more of the sense inputs during Phase 1 mode of operation serves to maintain the device operating in that mode.

Absence of stimuli from all sense inputs during Phase 1 mode of operation causes the device to transfer to Phase 2 mode of operation.

A stimulus presented to one or more of the sense inputs during Phase 4. mode of operation serves to maintain the device operating in that mode.

Absence of stimuli from all sense inputs during Phase 4 mode of operation causes the device to transfer to Phase 2 mode of operation.

A stimulus presented to one or more of the cancel inputs during Phaze 4 mode of operation causes no change in mode or output signals being generated.

2. A self-priming interlock/warning device according to claim 1 with the additional feature that a stimulus presented to one or more of the sense inputs during Phase 2 mode of operation causes the device to transfer to Phase 3 and remain in that phase for a pre-determined time period (during which a signal is generated on the cancel output) before advancing to Phase 4.

3. A self-priming interlock/warning device according to claim 1 or 2 with the additional features that the device remains in Phase 1 for a predetermined time period after the stimulus maintaining that mode of operation had been removed, and that the device remains in Phase 4 for a predetermined time period after the stimulus maintaining that mode of operation had been removed.

4. A self priming interlock/warning device according to claim 1, 2 or 3, with the features as arranged and substantially here in described with reference to the specification text.

5. A self-priming interlock/warning device according to claim 1, 2, 3 or 4, with the features as arranged and substantially here-in described with reference to the accompanying drawings.

6. A self priming interlock/warning device according to claims 1, 2, 3, 4, or 5 with the additional feature that a stimulus presented to one or more of the cancel inputs during Phase 4 causes the device to transfer to Phase 1 mode of operation.