GB2319408A

GB2319408A - Switching isolator for power supply loop

Info

Publication number: GB2319408A
Application number: GB9723415A
Authority: GB
Inventors: Kenneth William King
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-11-08
Filing date: 1997-11-06
Publication date: 1998-05-20
Also published as: GB9623277D0; GB9723415D0

Abstract

A dual isolator device 4 (and Figure 2 (not shown)), for association in parallel with a critical device 3 in a power supply loop circuit 5, comprises a short circuit detector for connection to the loop 5 for detecting the voltage change associated with a short circuit in the loop. Switching means are provided in the isolator device on each side of the critical device 3, so as to isolate the device from the power supply loop circuit on detection of a short circuit only on the side of the critical device in which the short circuit lies, thereby allowing operation to continue. The critical device 3 may be an alarm sounder, smoke detector, or a combination smoke detector and alarm sounder, or an intruder detector device, or a passive infra red detector, or an active movement detector, or a trembler or vibration detector, or a sound or video communication or surveillance device, or any other device that it is desirable to protect from cable faults. Isolations and non-isolations are retained in power off conditions. This allows continuity and resistance testing to take place without bypassing of the isolators.

Description

Dual Isolator and Circuit Protection system This invention relates to a dual isolator for use in electrical circuits.

In critical electrical circuits such as fire alarms it is imperative that power to the active elements of the system is maintained even under faulty wiring conditions.

This has previously been tackled by wiring power to elements such as smoke detection and alarm sounders in a ring which provides continuity of supply in an open circuit condition.

Unfortunately this offers no protection against short circuit faults.

Advances in technology and the need for wiring economy can mean several hundred critical devices being wired on a single loop. Methods of segregating faulty sections of short circuit wiring have been severely limited because of the technology available.

Previous attempted solutions to this problem have employed traditional semiconductor devices with inherent impedance which has limited their suitability to ensure the integrity of devices powered by the loop. Because of the inherent resistance and the often large number of loop powered devices it has not been possible to protect every element as the resulting volts drop from the connection of multiple protection devices falls below the safe working levels of the system and the number of such devices is limited to typically 20. The limitation of this is that a loop of say 200 devices could result in ten critical devices being lost in a short circuit condition.

The present invention aims to mitigate or eliminate these disadvantages of prior solutions and to provide the following advantages: The present invention allows short circuits to be isolated from each side of the load of a critical device in a circuit ensuring that continuity of supply is maintained to each such device in the event of a short circuit. The present invention also provides extremely low resistance in a circuit in its quiescent state so that the presence of the circuit protection devices provides no limitation to the number of critical devices in The circuit. The present invention provides a continuous conduction path without power in the circuit to facilitate testing. The present invention memorises previously detected short circuits during power down conditions and immediately reinstates the fault free part of the loop on powering up. The invention provides an indication of the position of any detected fault in the circuit and is resistant to intermittent faults.

The practicably negligible resistance of the isolator of the invention offers no restriction to the number that can be used. It is therefore possible to fully protect all essential elements on a loop ensuring that none are lost in a wiring fault condition. Furthermore it is possible to protect both sides of a critical element with a single device.

According to the present invention there is provided a dual isolator device, for association in parallel with a critical device in a short circuit isolator and detection system in a power supply loop circuit, comprising detection means for connection to the power supply loop circuit for detecting the voltage change associated with a short circuit in the power supply loop circuit and switching means for association with the power supply loop circuit on each side of the critical device wherein the said switching means serves to isolate the device from the power supply loop circuit on detection of a short circuit in the power supply loop circuit only on the side of the critical device in which the short circuit lies.

The invention also provides a short circuit isolator and detection system comprising a critical device for connection in a power supply loop circuit combined with the dual isolator device of the invention.

The invention further provides a power supply circuit incorporating the short circuit isolator and detection system of the invention.

Preferably, the dual isolator device comprises activator means and the detector means causes activation of power means to said activator means which in turn causes said switching means to enter into an open circuit condition. Further the activator means may be a coil of an electromechanical relay and the switching means may be a contact operated by the electromechanical relay which may be a mechanical latching relay.

The electromagnetic relay may have a set operating coil and an unset operating coil and the set operating coil is energiseable by the said activation of the power means on detection of a short circuit and the unset operating coil is energiseable on detection of healthy wiring conditions. Indicator means in the form of one or more light emitting diodes may be provided which signals as to the condition of the said side of the isolator device on which the short circuit may lie.

The dual isolator device may incorporate components which allow regulation or adjustment of the operation of the unset operating coil to prevent its operation in the event of intermittent short circuit faults and may further incorporate components adapted to reduce the impedance or capacitive effects of the critical device by introducing electronic delay into the operation of the unset coil.

The dual isolator device may incorporate a test switch component which is adapted to operate the said set coil without short circuiting or removing power from the critical device or devices and may further incorporate a latching switch circuit which permanently latches the operation of the said set coil, thereafter requiring manual activation of the unset coil.

In the case of a short circuit on the wiring the dual isolator will isolate on the affected side of the critical device ensuring that the faulty section of wiring only is isolated and that the critical device is powered and able to communicate its status from the healthy side of the ring. The critical device protected in this way may be an alarm sounder, smoke detector, or a combination smoke detector and alarm sounder device, or an intruder detector device, or a passive infra red detection device, or an active movement detector device, or a trembler or vibration detector, or a sound or video communication or surveillance device, or any other device that it is desirable to protect from cable faults. Isolations and non-isolations are retained in power off conditions. This allows continuity and resistance testing to take place without bypassing of the isolators.

The invention will now be described with particular reference the figures of the attached drawings in which: Figure 1 shows an embodiment of the invention in a typical arrangement comprising a control unit (1) which provides power to the contained or integral units (2). Although two contained or integral units are shown for illustrative purposes, there would normally be a large number of such devices in a typical arrangement. Each contained or integral unit (2) illustrated by the dotted line enclosure encompasses a critical operating element (3)and a dual isolator device (4).The connecting wiring is depicted by the continuos line (5).

Details of the electronic circuit which comprises the dual isolator (4) of the contained unit (2) are shown in figure 2. Not shown is an optional Triac which provides a facility for the dual isolator to permanently latch after operation. This requires then a manual reset and is a protection against repeated operation from repeated short circuits.

As the dual isolator device is a simple electromechanical device it lends itself to simple interfacing with the master control in order that it can be operated on demand.

The basis of the dual isolator is a mechanically latching relay with independent set/unset operating coils (marked isolate and reset coils in Figure 2). Operation of these coils enables an isolate on short circuit and de-isolate in healthy wiring conditions.

In the reset condition D & E are closed. Capacitor C1 is connected to the negative supply via contacts A.C. and is charged to near high side voltage via D3 & light emitting diode LED 1 or D4 & LED 2 and RI.

In a short circuit condition the voltage at C1 + is divided across the isolate coil and constant current diode A2 which opens contacts D. E. protecting the healthy side from the faulted side. Once this is done the LED, 1 or 2, depending on the side, will cease to illuminate indicating the direction of the faulty wiring. Contacts B. C. are also connected thus reconnecting the negative side of C1 via D13. Contacts A. C. are opened prohibiting current feed into the short circuit and maintaining a high potential across C1 Via R1 and D4 & LED2orD3 & LEDl.

Resetting will only occur once the voltage is detected on both sides of contacts D. E. via opto A and opto B which allows a current to the reset coil via D3, LED 1, and constant current diode Al. The sensitivity and operation of these optos can be regulated by C3 & C4 providing resistance to intermittent short circuits. A sample voltage is applied to the faulted side via R3 when contacts D. E. are opened allowing sensing of this voltage by the optos A or B when no short circuit is present. Once reset TR1 conducts due to the voltage across C2 fed via R4 connecting the load S to zero volts via D4 & LED2 or D3 & LED1. A delay is introduced in this connection by TR2 to allow for the capacitive inductive or other effects of a wide range of loads that may otherwise affect the correct operation. TR2 operates only when the gate input voltage rises on operation of the relay which holds the gate voltage to zero via A. C. or B. C. This discharges C2 and the load S cannot be re-applied until C2 recharges.

Test switch SW1 provides a local test facility by allowing current from C1 to operate isolate coil as previously described but without short circuiting the supply rails and removing power from critical devices and affecting communications.

Claims

1. A dual isolator device, for association in parallel with a critical device in a short circuit isolator and detection system in a power supply loop circuit, comprising detection means for connection to the power supply loop circuit for detecting the voltage change associated with a short circuit in the power supply loop circuit and switching means for association with the power supply loop circuit on each side of the critical device wherein the said switching means serves to isolate the device from the power supply loop circuit on detection of a short circuit in the power supply loop circuit only on the side of the critical device in which the short circuit lies.

2. A dual isolator device as claimed in claim 1 comprising activator means and wherein the detector means causes activation of power means to said activator means which in turn causes said switching means to enter into an open circuit condition.

3. A dual isolator device as claimed in claim 2 wherein the activator means is an electromagnetic means.

4. A dual isolator device as claimed in claim 3 wherein the activator means is a coil of an electromechanical relay.

5. A dual isolator device as claimed in claim 4 wherein the switching means is a contact operated by said electromechanical relay.

6. A dual isolator device as claimed in any of claims 1 to 5 constructed and adapted such that the said switching means is able to maintain power supply to the critical device via the power supply loop circuit on the side of the critical device opposite the detected short circuit on and during the open circuit condition of the said switching means.

7. A dual isolator device as claimed in claim 5, or claim 6 when dependent from claim 5, wherein the electromechanical relay is a mechanical latching relay.

8. A dual isolator device as claimed in claim 7 wherein the electromagnetic relay has a set operating coil and an unset operating coil and the set operating coil is energiseable by the said activation of the power means on detection of a short circuit and the unset operating coil is energiseable on detection of healthy wiring conditions.

9. A dual isolator device as claimed in any preceding claim wherein the dual isolator device incorporates indicator means which signals as to the condition of the said side on which the short circuit may lie.

10. A dual isolator device as claimed in claim 9 wherein the indicator means is one or more light emitting diodes.

11. A dual isolator device as claimed in any preceding claim when dependent from claim 8 wherein the dual isolator device incorporates components which allow regulation or adjustment of the operation of the unset operating coil to prevent its operation in the event of intermittent short circuit faults.

12. A dual isolator device as claimed in any preceding claim when dependent from claim 8 wherein the dual isolator device incorporates further components adapted to reduce the impedance or capacitive effects of the critical device.

13. A dual isolator device as claimed in claim 12 wherein the further components include components for introducing electronic delay into the operation of the unset coil.

14. A dual isolator device as claimed in any preceding claim wherein the dual isolator device incorporates a test switch component which is adapted to operate the said set coil without short circuiting or removing power from the critical device or devices.

15. A dual isolator device as claimed in any preceding claim wherein the dual isolator device further incorporates a latching switch circuit which permanently latches the operation of the said set coil thereafter requiring manual activation of the unset coil.

16. A short circuit isolator and detection system comprising a critical device for connection in a power supply loop circuit and a dual isolator device, as claimed in any preceding claim, associated with the critical device.

17. A short circuit isolator and detection system as claimed in claim 16 wherein the dual isolator device and the critical device are incorporated in the same housing and provide an integral device for connection into a power supply loop circuit.

18. A short circuit isolator and detection system as claimed in claim 17 wherein the connections and/or the terminals connecting the critical device in the said integral device are protected and laid out so as to prevent short circuit conditions arising in the critical device or its connections.

19. A short circuit isolator and detection system as claimed in any of claims 16 to 18 wherein the housing incorporates means for the display of indicator devices indicating the direction of a short circuit fault in a power supply loop circuit to which the integral device may be fitted.

20. A short circuit isolator and detection system as claimed in any of claims 16 to 19 wherein the or each critical device is a smoke detector device, or an alarm sounder device, or a combination smoke detector and alarm sounder device, or an intruder detector device, or a passive infra red detection device, or an active movement detector device, or a trembler or vibration detector, or a sound or video communication or surveillance device.

21. A power supply circuit incorporating a short circuit isolator and detection system as claimed in any of claims 16 to 20.

22. A power supply circuit incorporating a dual isolator device as claimed in any of claims 1 to 15.

23. A dual isolator device as claimed in claim 1 and substantially as hereinbefore described with reference to and as illustrated in Figures 1 and 2 of the accompanying drawings.

24. A short circuit isolator and detection system substantially as hereinbefore described with reference to and as illustrated in Figures 1 and 2 of the accompanying drawings.

25. A power supply circuit substantially as hereinbefore described with reference to and as illustrated in Figures 1 and 2 of the accompanying drawings.