Electricity: measuring and testing – Determining nonelectric properties by measuring electric...
Patent
1985-11-22
1987-10-06
Eisenzopf, Reinhard J.
Electricity: measuring and testing
Determining nonelectric properties by measuring electric...
324464, 340628, G01N 2700
Patent
active
046985867
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an electric particle detector for monitoring the atmosphere in buildings for example, especially for the detection of fires.
The problem of fire detection by the detection of ions is well known. Usually, the air in a room is ionized by means of a radioactive source or a periodic electric spark and the monitoring is carried out by measuring an ionic current. When there is a fire, heavy particles of smoke for example, are carried in the building to the detection chamber where they disturb the movement of ions by intercepting or blocking them. The ionic current measured then drops and this drop is used to set off an alarm. It should be noted that humidity also reduces the ionic current. To prevent the humidity from triggering false alarms, it is customary to provide a reference chamber that is protected from humidity, or to provide electronic compensation of the sensitivity of the detector. In this case it becomes very difficult to detect a smouldering fire, for example. In fact with fires which do not have a great release of heat, the currents of convection are not strong enough to transport the heavy particles to the detector within a reasonable time. Consequently, the response time of the detectors in the case of a smouldering fire is very long, and this is a drawback as regards safety regulations.
One of the objects of the present invention is to provide a detector in which, unlike known detectors, the presence of particles emitted by the start of a fire, for example, increases the current passing through the detector.
Another aim of the invention is to provide a detector of charged particles that is remarkably simple and is capable of operating from different types of supply with an extremely low consumption.
The invention relates to an electric particle detector of the type comprising a sensor with two electrodes supplied with electricity, characterised in that the said sensor has its operating point at a current of between 10.sup.-13 and 10.sup.-9 A, and in that the collection of ions by the said sensor causes an increase in the current passing through it.
According to other features of the invention:
the electrodes are formed by wires bent in the shape of the Greek symbol alpha (.alpha.);
one of the electrodes of the sensor is connected to the point of supply via the intermediary of a resistor of very high value, while the other electrode is connected to the measurement point and, from there, to earth (ground) via the intermediary of a resistor;
when the sensor is in operation, the collection of ions causes an increase in current in the sensor;
the sensor is supplied via the intermediary of at least one diode which is arranged to operate at the start of its characteristic and behaves like a resistance;
the sensor is connected to the measurement point via the intermediary of a resistor of high value, each of the end terminals of this resistor being connected to earth (ground) by a capacitor of very low value;
the wires forming the alpha-shaped electrodes have barbs.
The following have been illustrated in the drawings by way of example:
FIG. 1: a simplified electrical diagram of one embodiment of a charged particle detector according to the invention;
FIGS. 2-11: various embodiments of the electrodes of the detector of FIG. 1;
FIG. 12: a variant of the electrical diagram of FIG. 1;
FIG. 13: an enlarged view of an alpha-shaped electrode according to FIG. 5.
Referring to the drawings, there is illustrated a sensor 1 for charged particles, which constitutes the sensitive portion of the detector. The housing of this sensor is not shown. This housing must be open to receive the gases liable to pass through it and preferably comprises a grille allowing the gases and charged particles emitted by the commencement of a fire to pass through. The electrodes 2 and 3 of the sensor 1 will be described hereinafter.
The sensor 1 is connected to earth (ground) by a resistor 4 the value of which is, for example, of the order of 10 megohms.
There is provided between the sensor 1 and the resistor 4
REFERENCES:
patent: 3439261 (1969-04-01), Loh et al.
patent: 3439263 (1969-04-01), Broyle, Jr.
patent: 3728615 (1973-04-01), Hill et al.
patent: 4121105 (1978-10-01), Solomon
patent: 4336455 (1982-06-01), Bryant
patent: 4538137 (1985-08-01), Kimura
Dutertre-Laduree Daniel
Goldman Alice
Goldman Max
Roos Andre
Eisenzopf Reinhard J.
Mueller Robert W.
PGEP Professional General Electric Corp.
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