NZ243453A - Normally closed heat sensor switch for fire alarm triggers electronic latch with visual indicator - Google Patents

Description

243453 NEW ZEALAND PATENTS ACT, 1953 No.: 243453 Date: 6 July 1992 COMPLETE SPECIFICATION IMPROVEMENTS IN AND/OR RELATING TO A SWITCH AND/OR A DETECTOR AND/OR A DETECTOR SYSTEM We, PERTRONIC INDUSTRIES LIMITED, a company duly incorporated under the laws of New Zealand, of 20 Eastern Hutt Road, Wingate, Wellington, New Zealand hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- ———— S 7 r - 6 SEP 1993 RECEIVED 243453 This invention relates to a heat detector circuit detector and/or a detector system and has been devised particularly though not necessarily solely for use as a heat activated fire alarm system.

It is an object of the present invention to provide a heat detector circuit and/or a detector system which will at least provide the public with a useful choice.

Accordingly in one aspect the invention consists in a heat detector circuit for a fire alarm system including: a heat sensitive mechanical switch of the normally closed type; an electronic latch adapted to receive a trigger on opening of the heat sensitive switch to change the latch to an on condition notwithstanding any subsequent state of the heat sensitive switch; and a visual indicating means to indicate that the latch is in the on condition.

In a further aspect, the invention consists in a detector system comprising a plurality of detectors according to the preceding paragraph sequentially connected.

Preferably, the heat sensitive mechanical switch includes a b: metallic device. In a preferred form of the invention the visual indicating means comprises a light emitting diode. In a most preferred form of the invention, the electronic latch comprises a silicon controlled rectifier, or in particular, a sensitive gate silicon controlled rectifier.

To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting.

The invention consists in the foregoing and also envisages constructions of . V\ I- „y v. which the following gives examples. ^ ! ' c ■-J , 1S3B -2a- One preferred form of the invention will now be described with reference to the accompanying drawings in which, Figure 1 is a circuit diagram of one form of switch and/or heat detector according to one preferred form of the invention.

Figure 2 is a circuit diagram as in Fig 2 of an alternative switch and/or heat detector.

Figure 3 is a diagram as in Fig 1 and 2 of a still further alternative form of switch and/or heat detector, Figure 4 is a diagram as in Figs 1, 2 or 3 of a still further alternative form of switch and/or heat detector, m 43453 (C\4 bidiM %C Figure 5 is a diagram as in Figs 1, 2,3 or 4 of a still further alternative form of switch or detector, and Figure 6 is a circuit diagram of a detector system according to one preferred form of the invention.

In the preferred form of the invention a switch and/or a detector and/or a detector system are provided as follows.

Referring to the drawings, the drawings indicate a 24 volt system but of course this is a matter of choice. Referring to Fig 1 the switch and detector has an input output connector 1 for example a four pin input output connector. Pins 1 and 3 are connected through a first switch element 2 which in the preferred embodiment is normally in the closed position. In the preferred embodiment the first switch element 2 changes state, for example, opens when a substantially predetermined change in physical condition occurs. For example a heat sensitive member, for example, a bimetallic device, such as a bimetallic strip or disc is provided so that the first switch element 2 will open when a substantially predetermined temperature is reached in the environment in which the first switch element 2 is positioned. As a further example the switch 2 could be a manual call point fire alarm switch.

A latch and an operating means for the latch are provided. The operating means may comprise a second switch element switching on when the first switch element 2 opens and the latch is arranged to remain in a conducting state once the second switch element has turned the latch on notwithstanding any subsequent change of state of the first switch element 2.

In the embodiment of Fig 1 the second switch element comprises an opto-couplerp^which is connected between pin 1 and the common pins 2 and 4 of connector 1. The opto-coupler includes a pair of parallel diodes 5 arranged oppositely so that the device is substantially independent of the direction of current flow through it. The opto-coupler 4 as shown in Fig 1 is an opto transistor coupler which is connected between the base and the collector of a transistor 3 forming part of the latch. Thus if first switch element 2 is opened current will flow through the input side of the opto-coupler 4 which is connected in parallel to the first switch element 2. This will cause current to flow through the output side of opto-coupler 4 243453 from pin 1 to 2 through the transistor 3. That is to say transistor 3 is switched on. The latch further includes a further opto-coupler 6 the input to which is provided in the collector circuitry of transistor 3. The output of opto-coupler 6 is provided between the base and collector of transistor 3. Therefore when current flows in transistor 3 opto-coupler 6 is switched on and current flows through its output circuit. Should the first switch element 2 be closed opto-coupler 4 will turn off and current will no longer flow through its output however, the base and collector of transistor 3 are still connected through the output of opto-coupler 6 which will remain on thereby maintaining transistor 3 in an on position. A visual indication device is desirably provided to indicate that the latch is on and thus may preferably comprise a light omitting diode 7 connected between pin 1 and the emitter of transistor 3.

Once the latch is turned on it can be reset or turned off by removing power from pin 1 of the connector 1. That is by way of switching the system off and then on. If however the polarity of the connections at connector 1 are reversed an alarm condition will be given as a short circuit will occur as current flow will be reversed through zener diode 8.

In the embodiment of Fig 2 the transistor 3 and opto-coupler 6 are replaced by SCR 10. Thus when the opto-coupler 4 switches on through the opening of the first switching element 2 the voltage increases at the gate 11 of the SCR 10 thereby switching the SCR 10 on. The SCR 10 will then of course remain on until the system is depowered whereupon it will switch off.

Turning now to the construction of Fig 3 here the transistor switch 3 and opto-couplers 4 and 6 are replaced by a pair of opto triacs 15 and 16 connected in parallel and in which the diodes 17 and 18 are of mutually reversed polarity with respect to current flow. Again if the first switching element 2 is opened current will flow through one of the opto triacs 15 or 16 depending on the polarity of the connection and current will flow through the light emitting diode 7. Of course the opto triac once turned on will remain on until power is removed from the switch. It is of course possible to replace the two opto triacs 15 and 16 with a single opto triac containing a pair of diodes of opposite polarity with respect to current flow.

It is also of course possible to replace the opto triacs with opto SCRs or with a single opto SCR containing a pair of diodes of opposite polarity with respect to current flow.

In the embodiment of Fig 4 the second switch element is provided by transistor 20 and the latch by SCR 21. When first switch element 2 is closed the transistor 20 is turned off. When the first switch element 2 opens transistor 20 turns on. This generates a voltage across resistor 22 and SCR 21 is turned on. The SCR 21 latches to hold the detector in the alarm condition even if first switch element 2 recloses.

In a particular non-limiting example based on Fig 4 the transistor 20 may be a BC 546B, resistor 35 may be 390kfl, capacitor 36 O.l^F, and resistor 37 lOkfl. Resistor R 22 may be 2.2kQ and capacitor 38 0.1/tF. The SCR 21 may be a P0102AB and the zener diode 8 may be 36v. The resistors 39 and 40 may each be 220Q.

Referring to Fig 5 the latch comprises an SCR 45 with a sensitive gate. The SCR 45 (a P0109AB for example) has a gate trigger current of l^A compared to the P0102AB of Fig 4 which has a gate trigger current of 200/^A. This means that the circuit can be simplified by eliminating the drive transistor 20 used to amplify the trigger current drive in the circuit of Fig 4. Thus the operating means is provided by the circuit through capacitor 36 and resistor 46 which may be about 4kQ. Normally switch 2 is closed preventing SCR 45 from triggering and latching. When switch 2 opens the current which previous flowed through switch 2 now flows through the gate of the SCR 45 thus causing SCR 45 to turn on. The SCR 45 latches to hold the detector in the alarm condition even if the first switch 2 recloses.

The switches according to the preceding embodiments may be used in a detector system for example by providing a series of detectors 30 and 31 connected through their connectors 1. <£43453 A control unit 32 is provided the output of which is fed for example to pins 1 and 2 of the connector 1. From pins 3 and 4 an output is taken to the input pins 1 and 2 of the next detector.

This continued until the final detector in the sequence 33 is reached where the pins 3 and 4 of the connector 1 in the detector 33 are connected through an end of line resistor 34 the value of which is selected to suit the control equipment type.

When the first switch element 2 opens the detector operates and an alarm condition is sensed by the circuitry in control unit 32.

It is also possible to use the switch of the invention in respect of detectors which operate in a different mode. For example a smoke detector operates by providing in effect a short circuit between the in and out pins such as pins 1 and 3 of the connector 1 described above.

By suitably connecting the switch of the invention into the circuit again a short circuit condition in the smoke detector can be caused to turn the visual indicator such as light emitting diode 7 on and to latch the circuit so that the visual indicator remains on not withstanding that the short circuit condition ceases to exist.

In use the invention is utilised as follows.

In a detector system such as shown in Fig 5 the detector units including the switches are positioned for example in substantially the known manner. Thus for example in a heat operated fire alarm system the detectors can be positioned in the ceiling of selected rooms.

Should the room heat beyond a predetermined limit the switch element 2 will open turning on the second switching element causing the light emitting diode of the detector to switch on. That light, emitting diode will be latched on until power is removed from the circuit.

Thus it can be seen that at least in a preferred form of the invention a switch and/or a detector and/or a detector system are provided which has the advantage that in a system where the detector switching element is to be maintained in a normally closed position a visual indication can be given if the alarm situation occurs. It is ai oarticular advantage of the invention that the visual indication of an alarm condition will remain not withstanding that the events which caused the cr 4 3 4 5 3 alarm condition to occur have ceased. Thus the detector which caused the alarm signal to be given can be identified, and if required steps taken to remedy the factors which caused the alarm condition to occur. This is advantageous. 243453 8

Claims (15)

WHAT WE CLAIM IS:

1. A heat detector circuit for a fire alarm system including: a heat sensitive mechanical switch of the normally closed iype; an electronic latch adapted to receive a trigger on opening of the heat sensitive switch to change the latch to an on condition notwithstanding any subsequent state of the heat sensitive switch; and a visual indicating means to indicate that the latch is in the on condition.

2. The heat detector circuit as claimed in Claim 1 wherein the heat sensitive mechanical switch includes a bi-metallic device.

3. The heat detector circuit as claimed in Claim 1 or Claim 2, wherein the visual indicating means comprises a light indicating means.

4. The heat detector circuit as claimed in Claim 3 wherein the visual indicating means comprises a light emitting diode.

5. The heat detector circuit as claimed in any one of Claims 1-4 further including a second switch adapted to change state on opening of the heat sensitive switch to provide the trigger.

6. The heat detector circuit as claimed in Claim 5, wherein the second switch comprises an opto-coupler. 2.43 453

7. The heat detector circuit as claimed in Claim 5, wherein the second switch comprises an opto-triac.

8. The heat detector circuit as claimed in any one of the preceding claims, wherein the electronic latch comprises a silicon controlled rectifier.

9. The heat detector circuit as claimed in any one of Claims 1 - 4, wherein the electronic latch comprises a sensitive gate silicon controlled rectifier.

10. The heat detector circuit as claimed in Claim 5 or Claim 6, wherein the latch comprises a transistor and an opto-coupler, the output of said second switch being connected between the base and the collector of said transistor.

11. The heat detector circuit as claimed in Claim 7, wherein the latch comprises a second opto-triac, the diodes of both opto-triacs being of opposite polarity with respect to current flow.

12. A detector system including a plurality of heat detector circuits as c} ^ any one of the preceding claims, the heat detector circuits being sequentially ^ connected. r 1 .p o,

13. A detector system as claimed in Claim 12 further including a contf^ ^ to provide an alarm when an alarm condition is sensed by any of the heat detector circuits.

14. A heat detector circuit for a fire alarm system substantially as hereinbefore ^ described in connection with any one of Figures 1-5.

15. A detector system substantially as hereinbefore described in connection Figure 6 and any one of Figures 1-5. DATEDTHISo^Pd W»OF\^eCL PARK & SON L:\LIBRARY\WDH\SPECS\308210.TJH 1CANTS