JPS6242364Y2 - - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to a gas detection device.

BACKGROUND ART There are various types of gas alarm devices that quantitatively detect the occurrence of city gas leaks, refrigerant gas leaks from air conditioners, and other gases, which are already commercially available. These gas alarm devices issue an alarm when the gas concentration reaches a predetermined level, but because gas is measured regularly, minute amounts of gas that do not reach the predetermined level are ignored as being outside the measurement range. Currently, it is treated as something that cannot be measured.

However, there is often a need to detect whether or not there is a gas leak from a joint valve of a gas pipe, even if it is a minute amount of gas on the order of several PPM to several tens of PPM. In such cases, if you try to measure gas quantitatively, it will be affected by the atmosphere at the measurement location, and the display may give the impression that gas is being detected when there is actually no gas leak, or vice versa. A situation may occur in which a small amount of gas cannot be detected even though it is present.

This invention was developed to solve these problems, and it detects the presence of minute amounts of gas by floating the zero level, which is the reference point for gas detection, according to the atmospheric conditions at the gas detection location. The present invention provides a gas detection device that schematically displays gas concentration.

An embodiment of the present invention shown in the drawings will be described below.

FIG. 1 shows a block diagram of an embodiment of the gas detection device according to the present invention. The gas detection device includes a gas sensor 10 such as a semiconductor gas sensor, and the gas sensor is connected to a power source battery 12 through a constant voltage circuit 11.
More power is supplied.

When gas sensor 10 is contacted by a gas, as is well known and discussed in connection with FIG. 2, the sensor resistance decreases and its output voltage increases. Therefore, the output voltage of the gas sensor is a function of the gas concentration, and the increased voltage is given to the differentiating circuit 13.
The differentiating circuit 13 detects the amount of change in the rising voltage and supplies this as an output signal to the voltage amplifier 14 for voltage amplification. The amplified output signal is applied to voltage comparator 15.

The voltage comparator 15 is supplied with a constant voltage from the constant voltage circuit 11, generates a reference voltage from this constant voltage, and compares the reference voltage with the voltage signal input from the voltage amplifier 14. And if the voltage signal is equal to or exceeds the reference voltage, then
An output is generated from the voltage comparator 15 and displayed on the display 1.
6.

Indicator 16 responds to the signal from voltage comparator 15 to indicate that the gas sensor has detected gas. Display 16 may be any type of display device. In the embodiment, the display device is configured with a plurality of LED elements to provide a visual display.
This will be explained in connection with FIG.

According to the present invention, as described above, the gas sensor 10
When gas is detected, an output voltage is generated, and the output voltage is differentiated with respect to time by a differentiating circuit 13.
Therefore, the output signal does not include a DC voltage component, and a response from the DC voltage zero level is always obtained. Therefore, even if the atmosphere at the gas detection position changes over time, the gas can be detected in accordance with the atmospheric conditions, and when the detection device is brought close to the location where a gas leak is occurring, even a small amount of change in gas concentration will be detected. The value increases rapidly and can be clearly distinguished from the zero level, allowing gas detection.

FIG. 2 shows a partial circuit of the embodiment of the device of the present invention shown in FIG. Components in FIG. 2 that are the same as those in FIG. 1 are designated using the same reference numerals.

As described with reference to FIG. 1, a constant voltage is supplied from the power supply battery 12 to the gas sensor 10 through the constant voltage circuit 11. A well-known circuit can be used as the constant voltage circuit 11, and a constant voltage is applied to both terminals of the gas sensor 10.

The gas sensor 10 is illustrated as an oxide semiconductor gas sensor, and includes a semiconductor element S whose resistance changes as gas is adsorbed and desorbed, and a heater H that heats the semiconductor element.
A constant voltage is applied to the heater H from a constant voltage circuit 11, so that the heater H is heated at a constant rate. Further, a bias voltage is applied to the semiconductor element S from a constant voltage circuit 11.

Now, when gas comes into contact with the semiconductor element S of the gas sensor 10, its resistance decreases and the voltage of the load resistor R _L connected to the semiconductor element increases. This increased voltage is differentiated with respect to time by the differentiating circuit 13 as described with respect to FIG.

The differentiating circuit 13 consists of a capacitor C _T and a resistor R _T , to which backflow blocking diodes D ₁ and D ₂ are coupled. In such a differentiating circuit, the load resistance R _L
By differentiating the increased voltage, the amount of change in the increased voltage is detected. This differential output is applied to an operational amplifier _A1 constituting a voltage follower.

The output of operational amplifier _A1 is applied to a voltage amplifier (14 in Figure 1). This voltage amplifier contains an operational amplifier A ₂ with an input resistor R ₅ at its non-inverting input terminal.
The output signal of the differentiating circuit 13 is applied through the differential circuit 13.
On the other hand, the voltage supplied from the constant voltage circuit 11 is divided by the zero voltage adjustment variable resistor VR ₁ , and the voltage supplied from the constant voltage circuit 11 is divided by the variable resistor VR ₁ for zero voltage adjustment.
The zero compensation voltage obtained by the resistance ratio of _R2 is supplied to the inverting input terminal of the operational amplifier _A2 . This configuration compensates for the voltage drop across resistor R _T due to the offset voltage and bias current of operational amplifier _A1 .

In addition, the output voltage of the operational amplifier _A2 is divided by the span adjustment variable resistor _VR2 and the resistor _R6 , and the resulting voltage is negatively fed back to the inverting input terminal via the resistor _R4 . In this way, even if the span is adjusted by the variable resistor _VR2 , the output voltage can always be compensated for zero using only the offset voltage of the operational amplifier _A2 , and therefore only the differential signal voltage can be amplified by the voltage amplifier.

The output voltage signal of the voltage amplifier 14 is sent to the voltage comparator 1.
5 is input. On the other hand, a voltage stabilized by the constant voltage circuit 11 is applied to the voltage comparator 15 through resistors R ₇ and R ₈ . A voltage comparator 15 converts this voltage into several steps, in the illustrated example 10
It generates 10 reference voltages in steps. Each of these stepped reference voltages,
The voltage signal input from the voltage amplifier 14 is compared, and if the input voltage signal is higher than each reference voltage,
Output terminal 1 corresponding to the level of those reference voltages
Produces an output signal at ~10. Then, those output signals are sent to the corresponding input terminals 1 to 10 of the display 16.
is applied to

Although not shown in the drawings, the display device 16 has 10 light emitting diodes (LEDs) arranged in tandem in this embodiment, and each LED is connected to input terminals 1 to 10, respectively, in the form of an LED level meter. . For example, output terminals 1 to 6 of the voltage comparator 15
When an output signal is generated at input terminal 1 of display 16,
6 LEDs connected to ~6 will light up to indicate that the corresponding gas has been detected. Of course, when the gas sensor 10 detects a gas with a high concentration, all the LEDs of the display 16 will emit light, so in that case, the gas concentration cannot be known accurately, but the device of the present invention can quantitatively measure the gas. Rather, its purpose is to detect the presence of minute gas leaks, so its purpose can be easily achieved.

As described above, according to the present invention, the detection output of the gas sensor is differentiated with respect to time by the differential circuit, so that the zero level, which serves as the detection reference point, is set in accordance with the atmospheric conditions at the gas detection location. This eliminates unstable elements in gas detection, and even if the atmospheric conditions change, a response from zero level can always be obtained. Therefore, it is suitable for detecting the presence of minute amounts of gas.

Furthermore, the device of the present invention can be manufactured in a small size for convenient portability, and the presence of gas can be easily detected by carrying it to a desired location and bringing it close to a detection target.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the gas detection device of the present invention, and FIG. 2 is a circuit diagram of a main part embodying the embodiment of FIG. Explanation of symbols of main parts, 10...Gas sensor,
13...Differential circuit, 15...Voltage comparator, 16...
…display.

Claims (1)

[Claims for Utility Model Registration] 1. A semiconductor gas sensor whose resistance changes when gas comes into contact with it, a differentiation circuit that differentiates the voltage generated by the change in resistance of the semiconductor gas sensor, and a voltage amplifier that amplifies the differential output of the differentiation circuit. , a voltage comparator that compares the output voltage of the voltage amplifier with a reference voltage; and an indicator that indicates that gas has been detected based on the output signal of the voltage comparator. Detection device. 2. In the device according to claim 1 of the utility model registration claim, the voltage comparator compares the output voltage of the voltage amplifier with a plurality of reference voltages obtained by stepping the output voltage of the voltage amplifier into predetermined voltage steps, and compares the output voltage of the voltage amplifier with a plurality of reference voltages to determine whether the output voltage of the voltage amplifier is equal to or higher than the reference voltage. A gas detection device characterized in that it generates an output signal at an output terminal associated with each reference voltage. 3. In the device according to claim 2 of the utility model registration, the display device is formed by arranging a plurality of light emitting elements in a line, and the level of the corresponding light emitting element is adjusted according to the output signal generated at the output terminal of the voltage comparator. A gas detection device characterized by emitting light in a meter format. 4 Utility Model Registration In the device according to claim 1, the voltage amplifier includes a first operational amplifier as a voltage follower that inputs the differentiated output from the differentiating circuit, and amplifies the signal from the first operational amplifier. and a second operational amplifier that allows adjustment of the zero floating level of the output of the first operational amplifier and adjustment of the span of the differential signal.