JPH0140038Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor gas detection device, and more particularly to a device for detecting gas concentration in combustible gas based on an output signal output by a semiconductor gas detection element.

Conventional gas detection devices use electric pumps to directly draw in the sample gas for measurement, while others use semiconductor-type gas detection elements as seen in JP-A-52-63398 and eject compressed air from a nozzle. There are some types that use this ejection energy to suck the sample gas.

The present invention relates to an improvement of a gas detection device that employs the latter sampling method of sucking a sample gas using compressed air.

That is, the sampling method as seen in the above-mentioned Japanese Patent Application Laid-Open No. 52-63398 is effective in that it does not use a power source to suck the sample gas, but
When detecting gas concentration using a semiconductor gas detection element, it reacts sensitively even to low concentrations.
Normally, in places where gas atmospheres are likely to occur, there is a drawback that an alarm is issued even for values within the permissible range. Further, the semiconductor type gas detection element has a property of causing an output change depending on the humidity of the sample gas.

This invention is proposed in view of these points,
The first purpose is to dilute the sample gas with dilution air so that it will not react in the case of a low concentration sample gas. A second purpose is to adjust the humidity of the sample gas by using dehumidified dry air as the dilution air, thereby minimizing output changes due to changes in humidity.
In addition, the alarm set point can be stabilized by diluting the gas in the percent order, for which a large change in output cannot be obtained with a semiconductor sensor, and causing a larger change in output in the PPM order.

The configuration of the present invention will be described in detail below.The gist of the configuration is a measurement air line a that discharges measurement air from a dehumidifier via an ejector, a sample gas intake section, a filter, and a semiconductor via a flowmeter. a sample gas line b that reaches the formula gas detection section and is further connected to the negative pressure section in the measurement air line a;
and a dilution air line c that collects a portion of the measurement air discharged from the dehumidifier and mixes the collected measurement air with the sample gas entering the gas detection section via the flowmeter. , the accompanying drawings show examples.

In the figure, a indicates an air line for measurement, and a dehumidifier 1 and an ejector 2 for air drying (dehumidification) are inserted into this air line a, and the air for measurement is compressed. It reaches the ejector 2 and is then exhausted.

b is a sample gas line, and a sample gas suction part 3 is inserted at the tip of this line, a gas detection part 6 containing a filter 4, a flowmeter 5, and a semiconductor type gas detection element is inserted in the middle, and the end is the same as above. It is connected to the negative pressure section of the ejector 2.

c is a dilution air line, and this dilution air line c takes out a part of the dehumidified air flowing in the measurement air line a, and sends it to the sample gas line b via the flowmeter 7 to the gas detection unit 6. It is mixed into the sample gas entering the sample gas to dilute the sample gas, and the diluted concentration is monitored by flow meters 5 and 7, respectively.

The present invention has the above-mentioned configuration. Compressed air is supplied to the measurement air line a, and this compressed air is dehumidified in the dehumidifier 1 and exhausted through the ejector 2 via the line a. . This flow of compressed air causes a negative pressure effect on the negative pressure section within the ejector 2, and the sample gas is sucked from the suction section 3 of the sample gas line b connected thereto. The sucked sample gas passes through a filter 4, a flowmeter 5, and a gas detection section 6. Then, before reaching the gas detection unit 6, it is mixed with dehumidified diluted air sent through the diluted air line c.

Due to the above-described operation, the gas detection section 6 measures the concentration of the diluted sample gas, and according to the present invention, the following effects can be expected.

Since the concentration of the sample gas is diluted with the dehumidified dilution air, the reaction point can be arbitrarily set from the PPM to the LEL level depending on the dilution rate, and the reaction (alarm) can be stabilized.

Since the temperature and humidity of the sample gas can be adjusted and stabilized using the dehumidified dilution air, detection can be performed that is not significantly affected by the temperature and humidity of the sample gas.

[Brief explanation of the drawing]

The figure is a schematic system diagram of a gas detection device implementing the present invention. a...Measurement air line, b...Sample gas line, c...Dilution air line, 1...Dehumidifier, 2...Ejector, 3...Suction part, 4...Filter, 6...Gas detection Department.

Claims (1)

[Scope of Claim for Utility Model Registration] A measurement air line a that discharges measurement air from a dehumidifier via an ejector, and a semiconductor gas detection unit via a sample gas suction unit, filter, and flowmeter, Further, a sample gas line b connected to the negative pressure part in the measurement air line a and a part of the measurement air coming out of the dehumidifier are collected, and the collected measurement air is passed through a flowmeter. A semiconductor gas detection device comprising: a dilution air line c that mixes with the sample gas entering the gas detection section.