Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
1999-05-14
2001-11-20
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S338100, C250S339070, C250S324000, C250S559400
Reexamination Certificate
active
06320190
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
THIS INVENTION relates to an air shield for a particle detection system.
The invention is particularly suitable for, but not limited to, an air shield for a smoke detection system.
2. Prior Art
FIG. 1
discloses the operating principle of a known smoke detection system
The transmitter (
101
) in the detector (
100
) emits an invisible Infra-red (IR) pulse through the transmitter lens. The IR pulse traverses the measuring section and reaches the reflector (
102
) (eg., a prism) located opposite the detector (
100
). The reflector deflects the IR pulse back to the detector (
100
) where a receiver lens (
103
) directs the reflected IR pulse to a silicon photodiode (
104
). The resulting electrical signal is evaluated by the electronics.
If smoke (
110
) penetrates the measuring section, part of the IR pulse is absorbed by the smoke particles, while another part is scattered by the smoke particles. The remaining light reaches the reflector (
102
) and is then reflected and once again passes through the measuring section and is further attenuated. As only a small portion of the beam reaches the receiver (
103
), the signal becomes smaller.
The detection system disclosed in
FIG. 1
has the advantage over earlier systems, which had a transmitter at one end of the measuring section and a receiver at the other end of the measuring section, that a power supply and monitoring electronics need only be connected to the detector (
100
) at one end of the system. This is a significant saving where the measuring section, eg., in a large warehouse, may extend over 200 meters.
The problem with both known systems is that dust, smoke or other particles can cover the “windows” of the detectors and reflectors, degrading the performance of the detection systems and, in extreme cases, causing failure.
One suggestion has been to blow or direct a curtain of air across the beam windows, but this has proved unsuccessful as it has been found that the curtain of air actually draws dust or other particles from the surrounding air into the curtain, and these particles are deposited on the beam windows, merely delaying the period in which the build-up of dust or other particles on the beam windows becomes unacceptable.
SUMMARY OF THE PRESENT INVENTION
It is an object of the present invention to provide an air shield for a particle detection system component where a column of air is generated to prevent (or at least minimise) the contact of particles with the beam windows.
It is a preferred object of the present invention to provide an air shield where the air can be provided by the reticulated air supply found in most buildings.
It is a further preferred object to provide an air shield which is relatively inexpensive to manufacture, easy to install and requires minimal, if any, maintenance.
Other preferred objects of the present invention will become apparent from the following description.
In one aspect, the present invention resides in a method for shielding a component of a particle detection system from the particles, including the steps of:
mounting an air shield on the component, the air shield having a tubular body divided into first and second compartments by an intermediate wall, having a hole therethrough, the end of the body adjacent the first compartment being engageable with the component; and
applying pressurised air to the first compartment to pass through the hole and into the second component in a substantially stable column flow to prevent the ingress of particles into the tubular body.
In a second aspect, the present invention resides in an air shield for a component of a particle detection system including:
a tubular body, open at both ends, divided into first and second compartments by an Intermediate wall having a hole therethrough, the end of the body adjacent the first compartment being engageable with (or mountable on) the component; and
air diffuser means In the first compartment, connectable to a source of pressurised air; so arranged that:
a column of substantially stable air flows from the first compartment through the hole in the Intermediate wall, and through the second compartment and is expelled from the other end of the body to protect the component from the particles.
The shield is preferably formed from transparent plastics material, eg., perspex or polycarbonate, or from stainless steel. The body may be square, rectangular, circular, or other shape in end view and is preferably formed for releasable mounting on the component which it is designed to protect.
Preferably, the intermediate wall is spaced a distance of not less than 50 mm, more preferably 80 mm, from the other end of the tubular body in the second compartment. Preferably, the intermediate wall is spaced not less than 50 mm, more preferably at least 60 mm, from the beam window.
Preferably, at least one air diffuser unit is provided in the first compartment. More preferably, a plurality of the air diffuser units are arranged at substantially equal spacings within the first compartment.
Preferably, each air diffuser unit is of the type where air is diffused through a porous body to minimise any eddies or vortices within the first compartment.
Preferably, the air diffuser units are connected to a manifold which, in turn, is connected to a reticulated air supply (or a compressor).
Preferably, a filter/dryer unit is provided between the air supply source and the air diffuser units.
Preferably, the shape of the hole in the intermediate wall substantially conforms to the shape of the beam window on the component to which the air shield is to be mounted. Preferably, the hole is at least slightly larger than the beam window.
The air shield may be sealed to the component by a silicone sealant or other suitable sealing material.
Preferably, the placement of the air diffuser units, and the volume of air transmitted by the units, generates a stable column of air which passes through the hole in the intermediate wall and the second compartment to be expelled from the tubular body so as to prevent the ingress of any particles, eg., smoke or dust, into the air shield, and thereby preclude contact between the particles and the beam windows.
REFERENCES:
patent: 4340326 (1982-07-01), Buonauro et al.
patent: 5493117 (1996-02-01), Tamaki et al.
patent: 5517314 (1996-05-01), Wallin
Eilberg William H.
Hannaher Constantine
Israel Andrew
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