WO1996029592A1

WO1996029592A1 - Improvements relating to gas pollution detection equipment

Info

Publication number: WO1996029592A1
Application number: PCT/AU1996/000147
Authority: WO
Inventors: Alan Watts
Original assignee: Vision Systems Ltd.
Priority date: 1995-03-17
Filing date: 1996-03-15
Publication date: 1996-09-26
Also published as: AUPN179995A0

Abstract

A cross pipe pollution detector apparatus is disclosed for use as an aspirated smoke detector comprising a pair of air supplied pipes (5, 6) for receiving sample air aspirated therein from an area under pollution or smoke surveillance. The pipes (5, 6) being connected in an X formation junction with air flow to and from two of the arms through the junction (7), a light projector and a receiver positioned in respective other arms, whereby unscattered light from the projector is directed down one of the flow paths and not towards the receiver and is arranged across the path of the other flow path at the junction (7) formed in the pipes, the arrangement being such that the light in the junction will impinge upon particles appearing in the junction (7) to scatter the light thereby to be received by the detector.

Description

IMPROVEMENTS RELATING TO GAS POLLUTION DETECTION

EQUIPMENT

The present invention relates to a sampling chamber for a gas pollution detector particularly smoke detectors and sampling chambers therefor having a simplified construction.

Prior art pollution detectors comprise a sampling chamber of a specific construction comprising numerous components and parts and include means to absorb light. Great care has been taken in prior art sampling chambers to prevent the ingress of stray light on to the light detector, particularly light that has been reflected off internal walls of the sample chamber. Accordingly, it is necessary that the chamber is so constructed that only that light which is intended to impinge upon the detector surface is in fact received.

Prior art pollution detectors normally comprise a sampling chamber such as is described in Australian lapsed application 20510/76 by CSIRO and PMG; US patent no. 4607915, MT Cole; European patent application no. 92921559.8, MT Cole; and Australian patent application no. 642745 (Walter Kidde), to nominate some examples.

It is also known to provide optical point detectors utilising an LED display and a receiver cell located in relative position similar to the present arrangement although on a smaller scale. However, such known devices are relatively complex in as much as they employ labyrinths, insect screens and the like to absorb and isolate unwanted light and include an absorber opposite to the receiver. Furthermore, such known detectors are prone to dust build-up which leads to reduced sensitivity and, in some instances, false alarm. The present invention has a principal objective to provide a simple low- cost smoke detector/pollution detector in which the number of component parts are significantly reduced and yet relatively high sensitivity is achievable, particularly in relation to aspirated operation. In this regard it is preferred to have smoke samples drawn through the device rather than to depend upon unreliable ambient air currents to force smoke into the detector, as is commonly the case in the current art. The invention will be described in greater detail with reference to the accompanying drawings figures 1 and 2 which show two side elevations taken on two planes at 90° to one another of a smoke detector according to the present invention. Samples of air are pumped from throughout an area to be monitored via a pipe network which may be conventional and need not be enlarged upon here. Two lengths of the pipe network are fabricated into a cross configuration, as shown in Figure 1 of the sketches, to form a simple smoke detector. The bottom end of the pipe 5 is shown with a light projector mounted therein projecting directly along the pipe to what may be the gas inlet or outlet depending on the direction in which the air is being pumped. Thus, unscattered light produced by the light projector travels on down the pipe to be absorbed in the length of the pipe out of the vicinity of the light detector which is mounted in the top end of pipe 6, as shown. Associated with the detector is a focusing lens to focus scattered light that may be directed along the pipe 6 as a result of impingement of the light beam from the light projector on to particles in the gas that encroach into the crossover area of the two pipes 5 and 6, as shown in the dotted line 7. The bottom end of the pipe 6 may form the inlet or outlet for gas entering the zone.

The crossover configuration substantially shields the light receiver from direct projected light produced by the light projector so that only light scattered off airborne particles at the intersection of the pipes 7 is visible to the receiver. Projected light is subsequently dissipated down the pipe without requiring an absorber.

The angle of intersection of the pipes is preferably quite narrow and ideally in the range of 20° to 30°, preferably 25°, and is designed to emphasise detection of light at small angles to the axis of the projector beam to achieve optimum sensitivity.

An aspirator (not shown) is connected to one end of pipe 5 or 6. Optionally a dust filter (not shown) is provided upstream of the detector with the pipe network extending beyond the filter to minimise false alarms and reduce dust build up upstream of or ahead of the detector. With reference to Figure 1, the projector beam is confined by an orifice 10 formed by a knife-edge aperture formed by drilling the hole at an opposing angle to form the knife edge to minimise scattering of light projected through the orifice. There is also preferably provided a small D-shaped baffle 11 to assist in shading the projector orifice from the receiver. The receiver cell includes a preamplifier which may be contained in a module attaching to the end of the pipe.

It will be appreciated that air flow in the pipes 5 and 6 in the vicinity of the crossover is relatively unrestricted and quite direct causing the air to flow around the junction 7 that forms a relatively large radius bend causing only a slight change in direction of air flow. Accordingly, energy loss in the air flow system is minimal thereby increasing the aspiration efficiency of the system.

The open and unobstructed design of the system ensures that the light scattering volume 7 is quickly purged ensuring rapid dynamic response to changing smoke levels in the vicinity. Accordingly, the invention provides a construction which is simple, ensures good purging and, furthermore, does this with a minimum of parts and dispenses with the need for a light absorber, meaning that the effect of dust build-up is minimised and thereby increasing the periods between maintenance and overhaul. Furthermore, in view of the simplicity of the construction , cleaning is simplified.

It has been found that the sensitivity of the detector is equivalent to 1% per metre obscuration or better, which is appropriate for aspirated residential applications as well as a variety of commercial and industrial locations of moderate size. The high sensitivity of the device takes account of smoke dilution caused by sampling air from several locations, such as different rooms of a house, only one of which may contain any smoke or pollution. Furthermore, the unit is immune to air draughts and minimises dust build-up and, therefore, false alarms are minimised despite the relatively high sensitivity of the unit.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A pollution detector apparatus such as an aspirated smoke detector comprising at least a pair of air supply pipes for conducting sample air therein from an area under pollution or smoke surveillance wherein said pipes are interconnected in an X-formation junction with air flow to and from two of the arms through the junction, a light projector and receiver positioned in the respective other arms whereby unscattered light from the projector is directed down one of the flow paths and is arranged to cross the path of the other flow path at the junction formed in the pipes, the arrangement being such that light in the junction will impinge upon particles appearing in the junction to scatter the light and be received by the light receiver and detector.

2. Apparatus as claimed in claim 1 wherein the detector includes a focusing lens for focusing scattered light received onto the detector.

3. Apparatus as claimed in claim 1 or claim 2 wherein the projector beam is confined by an orifice in its flow path the periphery of the orifice being formed as a knife edge to minimise scattering of light projected through the orifice.

4. Apparatus as claimed in any preceding claim including a baffle member mounted adjacent to the junction and positioned and provided to shade light projected through the orifice from the detector.

5. Apparatus as claimed in any preceding claim wherein the detector includes a pre-amplifier circuit contain in module fitted into the end of the pipe