NZ585677A - An alarm detector indicator which provides an indication that an alarm sensor, when the terminals of the sensor are connected to a power supply, are conected with the correct polarity - Google Patents

Abstract

An alarm detector is disclosed, which comprises: a sensor switch responsive to an alarm condition, an indicator for providing a visible indication of an electrical connection between the alarm detector and an external supply, and at least three detector terminals for connection of the alarm detector to external circuitry. The sensor switch is connected between first and second detector terminals, and is normally closed but opens in response to the alarm condition. The indicator is in a polarity sensitive indicator circuit that is connected between the first detector terminal and a third detector terminal whereby the indicator provides the visible indication when the external supply is connected across the first and third detector terminals with one polarity but not with an opposite polarity.

Description

585677 1 Received at IPONZ 25/06/2010 NEW ZEALAND PATENTS ACT, 1953 No: Date: COMPLETE SPECIFICATION DETECTOR INDICATOR AND METHOD We, PERTRONIC INDUSTRIES LIMITED, a New Zealand company, of 17 Eastern Hutt Road, Wingate, New Zealand, do heteby 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: 2571858-1 585677 Received at IPONZ 25/06/2010 2 FIELD OF INVENTION The present invention relates to a detector with an indicator that provides an indication, for example a visible indication, of the supply voltage applied to the detector. The detector is 5 particularly useful when used with a plurality of like detectors, where each detector is connected to a common alarm condition monitoring station by a common line. Each detector may be sensitive to a fire hazard condition. In this application each detector is typically attached to a ceiling in a room, or other space, to be monitored for the fire hazard condition. Each detector may be sensitive to the presence of smoke particles or other 10 combustion or pre-combustion products, or may be a heat detector sensitive to radiant or convected heat energy.

BACKGROUND Fire hazard detectors are typically mounted to the ceiling of a room or other space to be monitored for a fire hazard.

In a typical domestic application, a unitary combination of a Hre detector and alarm is contained in a common housing mounted on a ceiling or other nearby surface. Typically, a 20 combined detector and alarm device is mounted in each of several rooms of a dwelling, apartment or other building to be monitored. These unitary detector and alarm devices can be powered by a battery located in the common housing to operate completely independently of other detectors or alarms in the building.

Alternatively, the detectors can be interconnected, for example to a common power source, or so that sensing of a fire hazard by any one detector in the common installation causes at least one, and preferably all, of die other interconnected devices to also provide a local alarm signal, thereby distributing the alarm signal throughout the building.

In relatively large installations, such as hospitals, educational institutions, residential apartments, and commercial or industrial buildings, interconnected detectors are mounted to ceilings or other surfaces throughout a building. Each detector monitors hazards in a respective zone. The zones typically overlap to provide comprehensive and substantially 25718584 585677 Received at IPONZ 25/06/2010 3 continuous monitoring throughout a building. Typically, groups of these detectors are connected to a common detector monitoring station which is connected to alarm signalling devices, for example bells or sirens. Each group of detectors is electrically connected to the monitoring station by a common line.

The monitoring station is typically located in the building and is optionally connected to one or more remote monitoring stations. If any one of the detectors detects a fire hazard condition, a local alarm signal is generated at the building and/or a remote off-site monitoring station is alerted. Typically, a monitoring station will also identify the particular 10 location of the detector or detectors that have detected the fire hazard condition. This location may be identified at the local monitoring station in the building, at a remote display device located at an exterior access point of the building, e.g. at a pre-arranged entry point for fire or other rescue services, and/or at the remote off-site monitoring station.

In large installations, it is difficult to ensure that all detectors are correctly connected to the monitoring station. Detectors may be incorrecdy connected, or not connected at all, to the common detector monitoring line on first installation, or may become disconnected from the common line after being initially correcdy connected.

Previous detectors have been provided with a normally reverse biased diode that causes an indication to be provided by the alarm monitoring station if a detector is incorrectly connected with reversed connections. The diode is reverse biased when the detector is correcdy connected to the normal monitoring voltage placed on the common detector line by the monitoring station.

If the detector connection to the line is reversed, the diode is forward biased by the normal alarm monitoring voltage and presents a relatively low resistance across the line. The alarm monitoring station recognises this low resistance as an alarm or fault condition and provides an appropriate indication of this status.

But this indication does not identify which of the many detectors connected on the common line is incorrecdy connected. Some previously-known detectors have also been provided with electrical test points at which a technician can take an electrical measurement 2571858-1 585677 Received at IPONZ 25/06/2010 4 to verify the connection of the respective detector across the common line and whether it is of the correct polarity. This verification can be onerous because in typical installations the detectors are mounted on a ceiling and the technician must climb a ladder to individually access each detector.

Previous detectors have also been provided with an indicator light, e.g. a light emitting diode (LED), that illuminates when a detector has sensed a fire hazard condition.

Electrical circuitry latches to maintain the illumination after cessation of the hazard condition. This allows a technician called out to investigate an alarm to identify the 10 particular detector that caused the alarm. The latching function is particularly useful when investigating a false alarm caused by an intermittent detector fault.

SUMMARY OF INVENTION An object of at least one embodiment of the invention is to provide a fire hazard detector with an indicator, or a method for verifying a connection between an alarm detector and an alarm monitor, or at least to provide the public with a useful choice.

In a first aspect the invention may be broadly said to be an alarm detector comprising: 20 • a sensor switch that is responsive to an alarm condition, • an indicator for providing a visible indication of an electrical connection between the alarm detector and an external supply, and • at least three detector terminals for connection of the alarm detector to external circuitry; wherein: • the sensor switch is connected between a first detector terminal and a second detector terminal, and is normally closed but opens in response to the alarm condition, • the indicator is in a polarity sensitive indicator circuit that is connected between the 30 first detector terminal and a third detector terminal, and 2571858-1 585677 Received at IPONZ 25/06/2010 • the indicator provides the visible indication when the external supply is connected across the first and third detector terminals with one polarity but not with an opposite polarity.

The alarm condition may be a fire ha2ard condition or a temperature exceeding a predetermined threshold temperature.

The visible indication may be an illumination. The indicator may be a light emitting diode.

In a second aspect the invention may be broadly said to be a method of providing a verification of a connection between an alarm detector and an alarm monitor, the alarm detector comprising a normally closed sensor switch that opens in response to an alarm condition, the method comprising: • connecting the alarm detector to the alarm monitor by an alarm circuit, • the alarm monitor supplying a voltage of a one polarity to the alarm circuit to put the alarm monitor and the alarm circuit in an alarm monitoring mode, and • the detector then providing: (a) a first visible indication at the detector if the sensor switch is closed and the detector is connected to the alarm circuit with a first polarity, or 20 (b) providing a second visible indication at the detector if the detector is not connected to the alarm circuit or is connected to the alarm circuit with a second polarity that is opposite the first polarity; wherein the first visible indication is an illumination from a light source and the second visible indication is absence of the illumination from the light source.

In the method of the second aspect, the light source is preferably a light emitting diode.

Preferably, the connection of the detector to the alarm circuit with the first polarity is an incorrect connection and the connection of the detector to the alarm circuit with the 2613701 585677 Received at IPONZ 25/06/2010 6 second polarity is a correct connection. More preferably, the method further comprises reversing, and thereby correcting, the incorrect connection of the detector to the alarm circuit if the detector provided the first visible indication when the alarm monitor was put in the alarm monitoring mode.

Preferably, the method of the second aspect further comprises: • the alarm monitor supplying a voltage of a polarity that is opposite to said one polarity to the alarm circuit to put the alarm monitor and the alarm circuit in an alarm circuit verification mode, and 10 • the detector then providing the first visible indication at the detector if the detector is connected to the alarm circuit with the second polarity, or providing the second visible indication at the detector if the detector is not connected to the alarm circuit or is connected to the alarm circuit with the first polarity.

In the method of the second aspect, the alarm detector may be responsive to a fire hazard condition or a temperature exceeding a predetermined threshold temperature.

The invention may further be said to consist in any alternative combination of parts or features mentioned herein or shown in the accompanying drawings. Known equivalents of 20 these parts or features which are not expressly set out are nevertheless deemed to be included.

The term 'comprising' as used in this specification and claims means 'consisting at least in part of, that is to say when interpreting statements in this specification and claims which 25 include that term, each feature prefaced by that term in each statement, needs to be present but other features can also be present. Related terms such as 'comprise' and 'comprises' are to be interpreted in the same manner.

The term 'fire hazard condition' as used in this specification and claims is to be understood 30 as referring to any products or radiation or other conditions related to flame, fire or combustion, or related to smoking, charring, smouldering or other pre-combustion that may precede onset of a flame. Similar or related terms are also to be interpreted in the same manner. 2571858-1 585677 Received at IPONZ 25/06/2010 7 BRIEF DESCRIPTION OF THE DRAWINGS Referring to the accompanying figure it will be appreciated that the invention may be 5 implemented in various forms and modes. Preferred embodiments of apparatus and methods according to the invention will be further described, with reference to the figure, by way of example only and without intending to be limiting, wherein; Figure 1 shows a schematic alarm circuit incorporating an alarm monitor connected to alarm detectors by an alarm circuit.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Figure 1 shows a schematic alarm circuit incorporating an alarm monitor connected to alarm detectors by an alarm circuit.

An alarm detector 10 comprises a sensor switch 12. The sensor switch is normally closed but opens in response to an abnormal alarm condition such as a temperature that exceeds a predetermined threshold temperature, or any other fire hazard condition.

The alarm detector has at least three terminals for connection to of internal detector components to circuitry external to the detector. The sensor switch 12 is connected between a first detector terminal 14 and a second detector terminal 16.

The alarm detector also comprises an indicator 18, which in the preferred embodiment 25 shown in Figure 1 is a light emitting diode (LED). The indicator is in a polarity sensitive indicator circuit which, in the preferred embodiment shown in Figure 1, comprises the indicator 18, a semiconductor diode 20 and a current limiting resistor 22, connected in series. The indicator circuit is connected between the first detector terminal 14 and a third detector terminal 24.

The LED 18 illuminates to provide a first visible indication at the alarm detector 10 when a voltage of one polarity is applied across the first and third terminals 14 and 24 of the detector, but provides a visibly distinct second indication by not illuminating when a 2571858-1 585677 Received at IPONZ 25/06/2010 8 voltage of an opposite polarity is applied across the first and third terminals of the detector. The two visibly distinct indications may be provided by distinct illuminations, for example, steady and intermittent illumination, illuminations of distinct colour.

The polarity sensitive indicator circuit is arranged so that the LED 18 provides an indication of a reversed polarity. The reverse polarity indicator LED 18 does not illuminate when a normal alarm monitoring voltage is applied to the alarm detector, but does illuminate if the polarity of the voltage applied to the detector is reversed.

The reverse breakdown voltage of the semiconductor diode 20 is greater than the typically very low reverse breakdown voltage of the reverse polarity indicator LED 18 and is connected in the series indicator circuit to increase the overall reverse breakdown voltage of die indicator circuit above the maximum expected applied voltage for which the alarm detector is rated.

The resistor 22 is connected in the series indicator circuit to limit current flow in the series indicator circuit to less than a predetermined value when a predetermined voltage is applied across the first and third terminals 14 and 24 of the alarm detector 10.

In the preferred embodiment shown in Figure 1, the alarm detector 10 also comprises internal circuitry 30 that is connected to the first detector terminal 14, second detector terminal 16 and third detector terminal 24. Various forms of diis circuitry are known and details of this circuitry do not form part of the current invention. Typically, when the alarm detector is connected to an external voltage supply, the internal circuitry 30 monitors 25 die status of the normally closed sensor switch 12. If the switch opens, a latching circuit (not shown) is triggered, activating a sensor indicator LED (not shown) which illuminates to indicate the opening of the sensor switch. Once activated, the sensor indicator LED remains illuminated, regardless of the subsequent status of the sensor switch, until the latching circuit is unlatched and reset by temporary removal of the supply voltage.

While the sensor switch is closed, the internal circuitry 30 presents a high resistance path between the first detector terminal 14 and the third detector terminal 24, and between the second detector terminal 16 and the third detector terminal 24. An opening of the sensor 257!858-1 585677 Received at IPONZ 25/06/2010 9 switch triggers the latching circuit and activates and illuminates the sensor indicator LED, putting a low resistance path between the first detector terminal 14 and the third detector terminal 24, and between the second detector terminal 16 and die third detector terminal 24.

The alarm detector 10 is connected to an alarm monitor 40 by a two wire alarm circuit comprising first alarm circuit wire 42 and second alarm circuit wire 44. In a typical alarm installation, multiple alarm detectors, for example alarm detector 10, second alarm detector 46, and further alarm detectors (not shown), are connected across the two wire alarm 10 circuit. The second and further alarm detectors may be substantially identical to the alarm detector 10 described above. The first alarm circuit wire 42 connects the normally closed sensor switches of each alarm detector together in series. The second alarm circuit wire 44 provides a common return connection back to the alarm monitor 40 from each alarm detector.

An end-of-line resistor 48 is connected between the first and second alarm circuit wires at the distal end of the alarm circuit at the last of the further alarm detectors.

The alarm circuit, with the multiple alarm detectors and the end-of-line resistor 48 connected as described above, presents a resistance approximately equal to that of the end-of-line resistor to the alarm monitor 40 when the alarm detectors are correcdy connected, each sensor switch is closed and each latching circuit is un-latched. This is the normal alarm condition monitoring state.

If either alarm circuit wire is broken, i.e. by an open circuit, the alarm circuit presents a resistance substantially higher than that of the end-of-line resistor to the alarm monitor 40. The alarm monitor recognises this as a fault condition and provides an appropriate indication or signal.

Alternatively, if any one of the detector sensor switches has opened and triggered its associated latching circuit, the alarm circuit presents a resistance substantially lower than that of the end-of-line resistor to the alarm monitor 40. The alarm monitor recognises this as an alarm condition and provides an appropriate indication or signal. 2571858-1 585677 Received at IPONZ 25/06/2010 As noted above, the polarity sensitive indicator circuit is arranged so that the reverse polarity indicator LED 18 does not illuminate when a normal alarm monitoring voltage is applied to the alarm detector, but may illuminate if the polarity of the voltage applied to the 5 detector is reversed. After initial installation of an alarm system, a reverse polarity detector connection test is conducted by setting the alarm monitor in the normal alarm monitoring mode.

In the alarm monitoring mode of the embodiment described above and shown in Figure 1, 10 the voltage on the alarm circuit wire 42 is made positive with respect to alarm circuit wire 44. If the alarm detector 10 is incorrecdy connected with the alarm circuit connections transposed, (for example with the first alarm circuit wire 42 connected to the third detector terminal 24 and the second alarm circuit wire 44 connected to the first detector terminal 14 or to the second detector terminal 16), the reverse polarity indicator LED 18 and 15 semiconductor diode 20 will be forward biased, illuminating the LED 18 and effectively putting resistor 22 across the alarm circuit. The resistance of the forward biased indicator circuit is approximately the same as that of indicator circuit resistor 22 which is substantially less than that of the end-of-line resistor 48. The alarm monitor will recognise this lower resistance as a fault or alarm condition and provide an appropriate signal, 20 preferably without raising a general alarm given that this test is merely to confirm that the initial installation is correct.

However, while the alarm monitor can recognise the faulty connection, and may be able to identify which of several alarm circuits has the incorrecdy connected detector, the alarm 25 monitor does not identify which of the multiple alarm detectors connected on a common two wire alarm circuit is incorrecdy connected.

By virtue of the reverse polarity indicator of the present invention, a technician can walk along the path of the two wire alarm circuit and visually check which alarm detector or 30 detectors present an illuminated reverse polarity indicator LED, indicating incorrect, transposed connections. The illuminated reverse polarity indicator LEDs are placed on the detectors to be readily visible by the technician standing at floor level, thus avoiding the 2571S58-1 585677 Received at IPONZ 25/06/2010 11 onerous task of ascending a ladder at each of many ceiling-mounted detectors before locating a faulty connection.

While the illumination of the reverse polarity LED 18 in this test indicates an incorrect 5 connection, it is to be understood that the lack of illumination of a reverse polarity indicator LED in this test does not indicate that the connection is necessarily correct. The lack of illumination of a reverse polarity indicator LED in this test could also indicate that the alarm detector is not connected at all.

A second verification test mode of the current invention can be used for confirming correct connection of all detectors. This test mode can be performed to verify the initial installation, but is particularly useful when periodically re-testing the alarm installation. In this alarm circuit verification test, the polarity of the voltage normally applied to the alarm circuit by the alarm monitor is reversed. In the alarm circuit verification test of the 15 embodiment described above and shown in Figure 1, the voltage on the alarm circuit wire 42 is then negative with respect to alarm circuit wire 44. At every alarm detector 10 that is correcdy connected back to the alarm monitor by the two wire circuit, the reverse polarity indicator LED 18 will be forward biased and will illuminate.

As in the first reverse polarity test, a technician can walk along the path of the two wire alarm circuit to visually check that the reverse polarity indicator LED of each alarm detector is illuminated, indicating the integrity of a correct connection, at least as far as the detector showing an illuminated reverse polarity indicator LED. As in the first reverse polarity test, the technician can avoid the onerous task of ascending a ladder, e.g. to 25 measure voltages on test points, at many ceiling-mounted detectors before locating a faulty connection.

It is to be understood that the lack of illumination of a reverse polarity indicator in the alarm circuit verification test indicates either that the connection back to the alarm monitor 30 is broken, or that the polarity of the connection of the detector to the two wire alarm circuit is reversed. If the first detector terminal 14 is connected via alarm circuit wire 42 to the alarm monitor 40, as shown in Figure 1, the lack of illumination of the reverse polarity indicator LED 18 in the alarm circuit verification test could also indicate that the sensor 2571858-1 585677 Received at IPONZ 25/06/2010 12 switch 12 is open and therefore faulty (assuming that the verification test is done when the sensor temperature is less than the predetermined alarm threshold temperature.

Table 1 shows the illumination status of the reverse polarity indicator LED 18 in the 5 preferred embodiment shown in Figure 1. The illumination status is shown for normal and reversed polarities of the alarm monitor voltage applied to the alarm circuit, and for the detector connected to the alarm circuit with correct and incorrect polarity, or disconnected.

Table 1 Status of reverse polarity indicator (LED 18 in Figure 1) Detector connection to alarm circuit Connected with correct polarity Disconnected (or sensor switch open) Connected with incorrect polarity Alarm monitor voltage normal polarity (Alarm monitoring mode and reverse polarity connection test) Not illuminated Illuminated Alarm monitor voltage reversed, polarity (Alarm circuit verification test) Illuminated Not illuminated In an alternative detector circuit arrangement (not shown), the connection of the alarm circuit to the first and second detector terminals is transposed with the first detector terminal 14 being connected via alarm circuit wire 42 to the alarm monitor 40. In this arrangement, the lack of illumination of a reverse polarity indicator in the alarm circuit verification test indicates either that the connection back to the alarm monitor is broken, or 15 that the polarity of the connection of the detector to the two wire alarm circuit is reversed. In this arrangement, the illumination status of the reverse polarity indicator LED 18 is not dependent on whether the sensor switch 12 is open or closed.

The reverse polarity indicator circuit could be made symmetrical by adding another 20 semiconductor diode (not shown in Figure 1) so that the detector could be wired with 2571B58-1 585677 Received at IPONZ 25/06/2010 13 either the first detector terminal 14 or the second detector terminal 16 connected by alarm circuit wire 42 to the alarm monitor 40, in which case the other of the first and second detector terminals would be connected, direcdy or through one or more other detectors, to the end of line resistor 48. In this symmetrical circuit arrangement, the anode of the 5 additional semiconductor diode would be connected to the anode of the semiconductor diode 20, and the cathode of the additional semiconductor diode would be connected to the second detector terminal 16. In this symmetrical arrangement, the illumination of the reverse polarity LED 18 is independent of the status of the sensor switch and independent of transposition of alarm circuit connections to the first and second detector terminals 14 10 and 16.

The alarm detector 10 may have more than three terminals for connection to external circuitry. For example, a remote indicator LED 50 may be connected between the third detector terminal 24, or the common return alarm circuit wire 44, and a fourth detector 15 terminal 52. The remote indicator LED 50 is an optional feature that is useful in situations where the detector may not be directly or readily visible, e.g. where the detector is mounted in a false ceiling space or in a duct. In these situations the remote indicator can be used to provide a remote indication in a more suitable location, e.g. an adjacent room. One or more such remote indicators can be used. For example, remote indicators such as LED 50 20 can be used to mimic the reverse polarity indicator LED 18 and/or and the sensor indicator LED described above.

The foregoing describes the invention with reference to one or more preferred embodiments. Alterations and modifications as will be obvious to those skilled in the art 25 are intended to be incorporated within the scope of the invention as defined in the accompanying claims. 2571858-1 585677 Received at IPONZ 25/06/2010 14

Claims (14)

WHAT WE CLAIM IS:

1. An alarm detector comprising: • a sensor switch that is responsive to an alarm condition, • an indicator for providing a visible indication of an electrical connection between the alarm detector and an external supply, and • at least three detector terminals for connection of the alarm detector to external circuitry; wherein: • the sensor switch is connected between a first detector terminal and a second detector terminal, and is normally closed but opens in response to the alarm condition, • the indicator is in a polarity sensitive indicator circuit that is connected between the first detector terminal and a third detector terminal, and • the indicator provides the visible indication when the external supply is connected across the first and third detector terminals with one polarity but not with an opposite polarity.

2. An alarm detector as claimed in claim 1, wherein the alarm condition is a fire hazard condition.

3. An alarm detector as claimed in claim 1 or claim 2, wherein the alarm condition is a temperature exceeding a predetermined threshold temperature.

4. An alarm detector as claimed in any one of the preceding claims, wherein the visible indication is an illumination.

5. An alarm detector as claimed in any one of the preceding claims, wherein the indicator is a light emitting diode. 2571*58-1 585677 Received at IPONZ 25/06/2010 15

6. A method of providing a verification of a connection between an alarm detector and an alarm monitor, the alarm detector comprising a normally closed sensor switch that opens in response to an alarm condition, the method comprising: 5 • connecting the alarm detector to the alarm monitor by an alarm circuit, • the alarm monitor supplying a voltage of a one polarity to the alarm circuit to put the alarm monitor and the alarm circuit in an alarm monitoring mode, and • the detector then providing: (c) a first visible indication at the detector if the sensor switch is closed and 10 the detector is connected to the alarm circuit with a first polarity, or (d) providing a second visible indication at the detector if the detector is not connected to the alarm circuit or is connected to the alarm circuit with a second polarity that is opposite the first polarity; wherein the first visible indication is an illumination from a light source and the second 15 visible indication is absence of the illumination from the light source.

7. A method as claimed in claim 6, wherein the light source is a light emitting diode.

8. A method as claimed in claim 6 or 7, wherein the connection of the detector to the 20 alarm circuit with the first polarity is an incorrect connection and the connection of the detector to the alarm circuit with the second polarity is a correct connection.

9. A method as claimed in claim 7, further comprising reversing, and thereby correcting, the incorrect connection of the detector to the alarm circuit if the detector 25 provided the first visible indication when the alarm monitor was put in the alarm monitoring mode.

10. A method as claimed in any one of claims 6 to 9, the method further comprising: • die alarm monitor supplying a voltage of a polarity that is opposite to said one 30 polarity to the alarm circuit to put the alarm monitor and the alarm circuit in an alarm circuit verification mode, and • the detector then providing the first visible indication at the detector if the detector is connected to the alarm circuit with the second polarity, or providing the 2613701 585677 Received at IPONZ 25/06/2010 16 second visible indication at the detector if the detector is not connected to the alarm circuit or is connected to the alarm circuit with the first polarity.

11. A method as claimed in any one of claims 6 to 10, wherein the alarm detector is 5 responsive to a fire hazard condition.

12. A method as claimed in any one of claims 6 to 11, wherein the alarm detector is responsive a temperature exceeding a predetermined threshold temperature. 10

13. An alarm detector substantially as hereinbefore described with reference to, and/or as illustrated in, the accompanying drawing.

14. A method of verifying a connection between an alarm detector and an alarm monitor, substantially as hereinbefore described with reference to, and/or as illustrated in, 15 the accompanying drawing. PERTRONIC INDUSTRIES LIMITED By the authorised agents AJ PARK 20 Per: 2613701