JP3334358B2 - Gas detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas detector for detecting incomplete combustion provided in a water heater using city gas, LP gas or kerosene as fuel.

[0002]

2. Description of the Related Art When a water heater using city gas, LP gas or kerosene as a fuel burns incompletely, a toxic gas such as carbon monoxide gas is generated, which may cause a gas poisoning accident. In order to prevent such an accident, it is effective to mount a carbon monoxide gas sensor in the flue of the water heater and to quickly detect carbon monoxide gas.

When detecting carbon monoxide gas in the flue of a water heater, the concentration of carbon monoxide gas is about 3000 ppm.
As long as the gas can be detected, the detection sensitivity concentration is 50pp
Although a highly sensitive and expensive carbon monoxide gas sensor cannot be used, a contact combustion type gas sensor which is a flammable gas sensor for home use can be used. The temperature range targeted by the household contact combustion type gas sensor is −20 to 40 ° C., but the temperature range when applied to a water heater is 70 to 230.
It is as high as ℃ and it is a wide area. This temperature range exceeds the temperature compensation range of the pair of gas detection element and temperature compensation element incorporated in the catalytic combustion type gas sensor, and the temperature compensation is insufficient. In order to enable gas detection even in this temperature range, another temperature measuring element is added and the output of the temperature measuring element and the output of the bridge circuit are calculated to perform temperature correction. When the resistors constituting the gas sensing element and the temperature compensating element are platinum, a small platinum thin film resistor for general temperature measurement is used as a temperature measuring element having the same temperature coefficient.
The gas detecting element, the temperature compensating element and the temperature measuring element are installed close to each other in the flue of the water heater so that no temperature difference occurs between the elements.

FIG. 3 shows a diagram of such a conventional high-temperature gas detection circuit. The gas detecting element 1 and the temperature compensating element 2 together with the balancing resistors 11 and 12 form four branches of a bridge circuit. A power supply E is connected to the bridge circuit.
Both ends of the series connection of the temperature measuring element 3 and the balance resistor 13 are connected to a power source E of a bridge circuit. The gas detection signal output of the bridge circuit is connected to the first differential amplifier 24. The temperature signal generated at the connection point of the temperature measuring element 3 with the resistor 13 and the output of the first differential amplifier 24 are input to the second differential amplifier 25. The output of the second differential amplifier 25 is a gas detection signal. The differential amplifiers 24 and 25 may be buffer amplifiers.

The output of the first differential amplifier 24, ie, the first
Since the temperature compensation is not sufficient in the high temperature range , the gas detection signal subjected to the temperature compensation is compared with the temperature signal from the temperature measuring element which is further input to the second differential amplifier 25 and input simultaneously. Thus, the gas detection signal subjected to the second temperature compensation is output to the output terminal of the high-temperature gas detection circuit. Generally, an output of the bridge circuit or the gas detection circuit when the gas detection element is not in contact with the gas to be detected is referred to as a zero-point output. Normally, the resistances 11, 12, and 13 are adjusted so that the zero point output becomes 0 at 25 ° C. Actually, since the thermal emissivity of the gas detecting element and that of the temperature compensating element are different, the deviation of the zero point output from zero increases as the temperature increases.

The gas detection operation is started after the zero point output reaches 90% of the saturation value in order to avoid false alarms. Therefore,
It is desirable that the zero-point output quickly reach the saturation value and that the zero-point output always be small in the operating temperature range .

[0007]

According to the above-described temperature correction method, in a circuit in which a temperature measuring element is added to a conventional bridge circuit, the first temperature compensation performed by the bridge circuit does not occur.
A second temperature compensation is performed by calculating a temperature signal from a temperature measuring element having a different property with respect to the temperature. This means that temperature compensation is performed between curves having different properties with respect to temperature. As a result, there is a problem that the deviation of the zero-point output at a high temperature becomes large.

It is an object of the present invention to solve the above-mentioned problems and to provide a gas detecting device which has a sufficient temperature compensation and a small deviation at a high temperature of zero point output.

[0010]

In order to achieve the above object, resistors are connected in series to the gas detecting element, the temperature compensating element and the temperature measuring element, respectively, and these serially connected bodies are connected in parallel to a common power supply. , a signal generated at a connection point between the resistor of each of the temperature sensing element measuring the gas sensing element calculated by the first differential amplifier, a signal generated at a connection point between the resistor of each of the temperature measuring element and the temperature compensating element first 2, and the outputs of the first and second differential amplifiers are calculated by the third differential amplifier, and the output is used as the gas detection signal output.

[0012]

In the gas detection device, if the gas detection circuit described above is used, a temperature curve of a differential amplifier output having a signal from the gas detection element and a signal from the temperature measurement element as inputs, and a temperature compensation element Since the temperature curve of the output of the differential amplifier having the signal from the temperature sensor and the signal from the temperature measuring element as input is close to a similar shape, the difference between them is further reduced by calculating with a differential amplifier. It is easy to make corrections.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A description will be given of an embodiment of a high-temperature gas detection circuit in which the temperature fluctuation of the zero point output is improved. FIG. 1 shows a high-temperature gas detection circuit diagram of the present invention. In this circuit, a resistance 11, a resistance 11, a temperature compensating element 2, and a
12 and 13 are connected in series, these series-connected bodies are connected in parallel to a common power supply, and a signal generated at each terminal of the gas detecting element 1 and the temperature measuring element 3 is operated by the first differential amplifier 21 to obtain a temperature. A signal generated at each of the other terminals of the compensating element 2 and the temperature measuring element 3 is operated by a second differential amplifier 22, and outputs of the first and second differential amplifiers 21 and 22 are output to a third differential amplifier. 23, the output is used as a gas detection signal output, and the output terminal 31
Output to This circuit was assembled with a gas sensor using a conventional platinum temperature measuring resistor as a temperature measuring element, and the respective resistance values were adjusted so that the zero point output became 0 at 25 ° C. The gas sensor was placed in a thermostatic chamber set at the measurement temperature, and the saturation value of the zero-point output was measured.

FIG. 2 is a graph showing the temperature dependence of the resulting zero-point output.
Shown in The horizontal axis is the ambient temperature (scale on ° C.), and the vertical axis is mV at zero point output. Curve c shows the case of the temperature measuring element of the present invention and the conventional platinum thin film resistor temperature measuring element, and curve d shows the case of the conventional high-temperature gas detection circuit. From this figure, it can be seen that, for example, at an ambient temperature of 250 ° C., the zero-point output is 8 mV in the conventional high-temperature gas detection circuit, whereas the zero-point output is reduced to 2 mV in the case of the present invention, which is an improvement.

[0019]

【The invention's effect】

With the gas detection circuit described above, the differential amplifier output of the signal from the gas detection element and the signal from the temperature measurement element, the signal from the temperature compensation element and the signal from the temperature measurement element Since the differential amplifier calculates the similarity curve with respect to the temperature of the differential amplifier output from the differential amplifier output from the differential amplifier output, a gas detection device having a zero-point output and a small deviation at high temperature can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram of a high-temperature gas detection circuit according to the present invention.

FIG. 2 is a temperature dependence diagram of a zero-point output.

FIG. 3 is a diagram of a conventional high-temperature gas detection circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gas detection element 2 Temperature compensation element 3 Temperature measuring element 11 Resistance 12 Resistance 13 Resistance 21 First differential amplifier 22 Second differential amplifier 23 Third differential amplifier 14 Resistance 15 Resistance 16 Resistance 24 First difference Dynamic amplifier 25 Second differential amplifier 31 Output terminal E Power supply a 0-point output of temperature measuring element of the present invention b 0-point output of conventional temperature measuring element c 0-point output of high-temperature gas detection circuit of the present invention d 0-point output of conventional high-temperature gas detection circuit e 0-point output of temperature sensor of the present invention f 0-point output of conventional temperature sensor

Claims (1)

(57) [Claims] A resistor is connected in series to each of a gas detecting element, a temperature compensating element, and a temperature measuring element. of the signal generated at the connection point calculated by the first differential amplifier, it calculates the <br/> generated signal to the connection point of the resistance of each of the temperature measuring element and the temperature compensating element in the second differential amplifier, A gas detection device wherein the outputs of the first and second differential amplifiers are operated by a third differential amplifier, and the output is used as a gas detection signal output.