JPS6213621B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a smoke or gas concentration detection device, and in particular to a smoke or gas concentration detection device that can make the concentration versus detection output characteristic close to a straight line.

Generally, so-called metal oxide semiconductor detection elements are known as devices that detect reducing gases such as smoke or gas by combining ZnO or other metal oxides and a heater.

Conventionally, in a smoke or gas concentration detection device using the metal oxide semiconductor detection element described above, as shown in FIG. , one in which the voltage across the load resistor 3 is measured is known. Note that 4 is a power supply for the heater of the detection element. Such a detection device has the disadvantage that it is not suitable for measuring high concentrations because the smoke or gas concentration vs. measurement voltage is saturated at high concentrations, as shown in FIG. 3a.

In the above-mentioned detection device, a correction circuit is required to make the relationship between smoke or gas concentration and measured voltage close to a straight line, which makes the circuit complicated, and the correction circuit is necessary to compensate for uneven characteristics of individual detection elements. Adjustment is required to match.

The present invention eliminates the above-mentioned drawbacks,
The relationship between the smoke or gas concentration and the measured value can be made close to a straight line without using the above-described correction circuit, and is particularly suitable for measuring high concentrations.

An embodiment of the present invention will now be described in detail with reference to FIG.

In FIG. 2, reference numeral 5 denotes the above-mentioned detection element, to which a DC power source 6 and resistors 7 and 8 are connected in series. 9 is a transistor, the collector of which is connected to the connection point between the resistors 7 and 8, the emitter connected to the connection point between the detection element 5 and the DC power supply 6, and the base fixed to both ends of the detection element. Variable resistor 10 with terminals connected
is connected to the movable terminal of the Reference numeral 11 denotes a power source for the heater of the detection element 5.

In the above device, when the internal resistance of the detection element 5 changes due to smoke or gas, the voltage between the fixed terminals of the variable resistor 10 changes, and the base current of the transistor 9 changes due to this change. Constant voltage means is configured to control the voltage applied to the detection element by the transistor 9 at a constant level so that the conductivity of the transistor 9 is changed and the voltage across the detection element 5 is held constant. . That is, when the variable resistor 10 is adjusted so that the transistor 9 is slightly conductive when the smoke or gas concentration is at the higher limit of the range to be measured and the internal resistance of the detection element 5 is low, the concentration As the internal resistance becomes lower and the internal resistance becomes higher, the terminal voltage of the detection element 5 increases, the degree of conductivity of the transistor 9 increases, the voltage drop across the resistor 7 increases, and the terminal voltage of the detection element 5 becomes approximately held constant. By keeping the terminal voltage of the detection element 5 constant in this way, the linearity of the current flowing through the detection element 5 in response to smoke or gas concentration, that is, the voltage measured across the resistor 8, is improved as shown in FIG. 3b. It becomes what is given.

Adsorption occurs on the surface of the metal oxide semiconductor element 5 in proportion to the surrounding gas concentration, and free electrons are generated within the crystal in proportion to the amount of adsorption, thereby changing the electrical conductivity. Therefore, by measuring the value of the flowing current while keeping the terminal voltage of the detection element 5 constant, it is thought that a characteristic close to a straight line that is approximately proportional to the gas concentration will be exhibited.

In the above embodiment, a parallel type constant voltage circuit in which the detection element 5 is considered as a load is exemplified. It can also be held constant.

As described above, the present invention can make the smoke or gas concentration vs. measured value characteristic nearly linear without using a correction circuit, and is particularly suitable for high concentration measurements because it does not saturate even at high concentrations. A smoke or gas concentration detection device can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a conventional example, Fig. 2 is a circuit diagram showing an embodiment of the present invention, and Fig. 3 is a comparison of smoke or gas concentration versus measured voltage between the conventional one and the present invention. This shows the characteristic curve. 5...Detection element, 6...DC power supply, 7, 8, 1
0...Resistor, 9...Transistor.

Claims (1)

[Claims] 1. A smoke or gas concentration detection device using a reducing gas detection element made of a metal oxide semiconductor, comprising: a DC power source that applies voltage to the detection element; a constant voltage means that controls the voltage across the detection element to a constant voltage;
A detection device comprising: means for measuring a current value flowing through the detection element whose both ends voltage is controlled to be constant, and smoke or gas concentration is detected based on the measured current value.