GB2145229A

GB2145229A - Heat detecting arrangement

Info

Publication number: GB2145229A
Application number: GB08322397A
Authority: GB
Inventors: Eric Macdonald
Original assignee: EMI Ltd
Current assignee: EMI Ltd
Priority date: 1983-08-19
Filing date: 1983-08-19
Publication date: 1985-03-20
Also published as: GB2145229B; GB8322397D0

Abstract

The heat detector consists of a bridge circuit including two temperature dependent components 1 and 2, one of which is arranged to respond more quickly than the other to increase in the temperature of a region being monitored. The components 1 and 2 are thin/thick film resistors directly deposited or provided in chip form on the longitudinal extremities of a long, thin substrate 3 formed of alumina. The substrate 3 carries on its surface two resistors, 4 and 5, of fixed resistance, which are interconnected with elements 1 and 2 in known manner. In an alternative arrangement substrate 3 is a printed circuit board supporting discrete components and providing a thermal gradient there-along. Additional electrical components 6, active and/or passive in nature, are provided on the substrate 3 to respond to the output signals from the bridge circuit when a temperature and/or rate of temperature rise is exceeded to produce alarm and/or other activation signals. <IMAGE>

Description

SPECIFICATION Heat detecting arrangements This invention relates to a heat detecting arrangement, which may be sensitive to the rate of increase of temperature in a region monitored by the arrangement and/or to the temperature in the region exceeding a predetermined threshold value.

The invention is especially relevant to such arrangements incorporating bridge circuits in which one or more heat-sensitive electrical components are deployed so as to be exposed to the temperature in the region to be monitored and connected with other components of the bridge circuit to cause, usually, the generation of out-of-balance signals when the prescribed conditions of potential hazard occur. The bridge circuit may alternatively or additionally be constructed so as to generate a signal when balanced. These signals are then utilised to initiate an alarm sequence and/or to actuate the automatic release of extinguishant. An object of the invention is to provide a heat detector arrangement including a bridge circuit which is reliable and rugged in operation yet economic to produce.

According to the invention there is provided a heat detecting arrangement including electrical components interconnected to form a bridge circuit, said components being supported on an elongate substrate with temperature dependent components of said circuit disposed at, or adjacent, either end of said substrate and temperature insensitive components of said bridge circuit disposed at convenient locations on [adjacent the long edges] of said substrate to form an integral unit.

In order that the invention may be clearly understood and readily carried into effect, one embodiment thereof will now be described, by way of example only, with reference to the accompanying drawing, the single figure of which shows, in schematic form, part of a bridge circuit which may be included in a detector arrangement in accordance with the invention.

The bridge circuit includes two temperature dependent components 1 and 2, one of which is arranged to respond more quickly then the other to increase in the temperature of a region being monitored. The components 1 and 2 may be semiconductive, resistive or a combination of both, and they are directly bonded at or adjacent the longitudinal extremities of a long, thin substrate 3 formed, for example, of alumina. The substrate 3 has, in this example, dimensions of 1.3" x 0.3" (3.30 x 0.76 cm) and it also carries, at any convenient location on its surface, two resistors, 4 and 5, of fixed resistance, which are interconnected with elements 1 and 2 in known mannertoform a bridge circuit.

As indicated schematically by the dashed rectangle 6, additional electrical components, active and/or passive in nature, can be provided on the substrate 3 to respond to the output signals from the bridge circuit to produce alarm and/or activation signals constituting output information in a desired format for remote sensing or locally latching systems.

In the event that such components 6 are provided on the substrate 3, for example in the form of a dual in-line (DIL) integrated circuit package, it can be advantageous to dispose such components adjacent to that one of the elements 1 and 2 which is desired to respond the more slowly to increases in temperature of the monitored regions. This expedient provides, wholly or in part, the thermal lagging required to provide the desired thermal gradient along the substrate. If necessary, further thermal lagging can be achieved by coating the appropriate element with an epoxy material. Clearly coating or otherwise encapsulating the relevant element with other suitable materials would be possible without departing from the scope of this invention.

In one form of implementation, the elements 1 and 2 comprise thin/thick film resistors either directly deposited on to the substrate 3 or provided in "chip" form and bonded to the substrate 3. The fixed resistors 4, 5 are thick film resistors and these are preferably trimmed actively (i.e. with an operating voltage applied to the bridge circuit) to give either a balance or a desired degree of imbalance as required to suit the design of the heat detector arrangement as a whole. Components 1 and 2 may also be trimmed, either individually or actively, for matching purposes.

As stated hereinbefore, the arrangement may respond when the rate of rise of temperature in the monitored region exceeds a predetermined value, or when the temperature exceeds a predetermined value or when both criteria are satisfied.

In an alternative embodiment of the invention, the substrate 3 is constituted by a printed circuit board supporting discrete components and providing a suitable thermal gradient there-along.

1. A heat detecting arrangement including electrical components interconnected to form a bridge circuit, said components being supported on an elongate substrate with temperature dependent components of said circuit disposed at, or adjacent, either end of said substrate and temperature insensitive components of said bridge circuit disposed at convenient locations on said substrate, thereby to form an integral unit.

2. A heat detecting arrangement according to Claim 1, wherein one or more of the electrical components forming the bridge circuit is a thin/thick film device directly deposited onto the substrate.

3. A heat detecting arrangement according to Claim 1 or Claim 2, wherein one or more of the electrical components forming the bridge circuit is a discrete component bonded to the substrate.

4. A heat detecting arrangement according to any one of the preceding Claims wherein the substrate is constituted by a printed circuit board which provides a suitable thermal gradient therealong.

5. A heat detecting arrangement according to any one of the preceding Claims, wherein the bridge circuit includes two temperature dependent components, one of which is arranged to respond more quickly than the other to increase in the temperature

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Heat detecting arrangements This invention relates to a heat detecting arrangement, which may be sensitive to the rate of increase of temperature in a region monitored by the arrangement and/or to the temperature in the region exceeding a predetermined threshold value. The invention is especially relevant to such arrangements incorporating bridge circuits in which one or more heat-sensitive electrical components are deployed so as to be exposed to the temperature in the region to be monitored and connected with other components of the bridge circuit to cause, usually, the generation of out-of-balance signals when the prescribed conditions of potential hazard occur. The bridge circuit may alternatively or additionally be constructed so as to generate a signal when balanced. These signals are then utilised to initiate an alarm sequence and/or to actuate the automatic release of extinguishant. An object of the invention is to provide a heat detector arrangement including a bridge circuit which is reliable and rugged in operation yet economic to produce. According to the invention there is provided a heat detecting arrangement including electrical components interconnected to form a bridge circuit, said components being supported on an elongate substrate with temperature dependent components of said circuit disposed at, or adjacent, either end of said substrate and temperature insensitive components of said bridge circuit disposed at convenient locations on [adjacent the long edges] of said substrate to form an integral unit. In order that the invention may be clearly understood and readily carried into effect, one embodiment thereof will now be described, by way of example only, with reference to the accompanying drawing, the single figure of which shows, in schematic form, part of a bridge circuit which may be included in a detector arrangement in accordance with the invention. The bridge circuit includes two temperature dependent components 1 and 2, one of which is arranged to respond more quickly then the other to increase in the temperature of a region being monitored. The components 1 and 2 may be semiconductive, resistive or a combination of both, and they are directly bonded at or adjacent the longitudinal extremities of a long, thin substrate 3 formed, for example, of alumina. The substrate 3 has, in this example, dimensions of 1.3" x 0.3" (3.30 x 0.76 cm) and it also carries, at any convenient location on its surface, two resistors, 4 and 5, of fixed resistance, which are interconnected with elements 1 and 2 in known mannertoform a bridge circuit. As indicated schematically by the dashed rectangle 6, additional electrical components, active and/or passive in nature, can be provided on the substrate 3 to respond to the output signals from the bridge circuit to produce alarm and/or activation signals constituting output information in a desired format for remote sensing or locally latching systems. In the event that such components 6 are provided on the substrate 3, for example in the form of a dual in-line (DIL) integrated circuit package, it can be advantageous to dispose such components adjacent to that one of the elements 1 and 2 which is desired to respond the more slowly to increases in temperature of the monitored regions. This expedient provides, wholly or in part, the thermal lagging required to provide the desired thermal gradient along the substrate. If necessary, further thermal lagging can be achieved by coating the appropriate element with an epoxy material. Clearly coating or otherwise encapsulating the relevant element with other suitable materials would be possible without departing from the scope of this invention. In one form of implementation, the elements 1 and 2 comprise thin/thick film resistors either directly deposited on to the substrate 3 or provided in "chip" form and bonded to the substrate 3. The fixed resistors 4, 5 are thick film resistors and these are preferably trimmed actively (i.e. with an operating voltage applied to the bridge circuit) to give either a balance or a desired degree of imbalance as required to suit the design of the heat detector arrangement as a whole. Components 1 and 2 may also be trimmed, either individually or actively, for matching purposes. As stated hereinbefore, the arrangement may respond when the rate of rise of temperature in the monitored region exceeds a predetermined value, or when the temperature exceeds a predetermined value or when both criteria are satisfied. In an alternative embodiment of the invention, the substrate 3 is constituted by a printed circuit board supporting discrete components and providing a suitable thermal gradient there-along. CLAIMS

5. A heat detecting arrangement according to any one of the preceding Claims, wherein the bridge circuit includes two temperature dependent components, one of which is arranged to respond more quickly than the other to increase in the temperature of a region being monitored.

6. A heat detecting arrangement according to any one of the preceding Claims, wherein additional electrical components, active and/or passive in nature, are provided on the substrate to respond to the output signals from the bridge circuit to produce alarm and/or activation signals constituting output information in a desired format for remote sensing or locally latching systems.

7. A heat detecting arrangement according to Claims 5 and 6 in combination, wherein the additional electrical components 5 are located adjacent to that one of the two temperature dependent components which is desired to respond the more slowly to increases in temperature of the monitored regions.

8. A heat detecting arrangement according to Claim 6 or Claim 7, wherein the additional electrical components are provided on the substrate in the form of a dual in-line integrated circuit package.

9. A heat detecting arrangement substantially as hereinbefore described with reference to and as illustrated in the sole accompanying drawing.