JPH0241741Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention is a gas leak alarm device that has a protection circuit that protects a catalytic combustion type gas sensor from high-temperature heat generation caused by contact with high-concentration gas, and a deterioration display circuit that indicates deterioration of the gas sensor. Regarding.

In conventional gas leak alarms, in the case of catalytic combustion type gas sensors, the gas detection part consists of a Wheatstone bridge circuit that includes the gas sensor, and a constant voltage circuit is connected to the bridge circuit to keep the gas sensor at an appropriate temperature. I'm trying to heat it up.
A comparator is connected to the balanced output of the bridge circuit, and is configured to sound an alarm such as a buzzer when the gas sensor comes into contact with a predetermined concentration of gas.

In such conventional gas leak alarms,
When a catalytic combustion gas sensor comes into contact with flammable gas, combustion occurs on the sensor surface, and this combustion heat increases the electrical resistance of the platinum heater wire inside, and the change in resistance is extracted as an unbalanced voltage in the bridge circuit. ing. Therefore, when a highly concentrated combustible gas comes into contact with such a sensor, combustion heat proportional to the concentration is generated, and the sensor generates heat at a high temperature. If this state continues for a long time, it may be difficult to restore the initial characteristics when the flammable gas disappears, and in severe cases, the sensor may burn out. As a result,
The zero point of the bridge circuit drifts, significantly reducing the functionality of the detection circuit, and this drift never recovers.

Furthermore, if a gas sensor is used for a long period of time under adverse conditions of high temperature and humidity, it may deteriorate and the zero point of the bridge circuit may drift. This phenomenon also reduces the performance of the alarm as a security device.

As mentioned above, in conventional gas leak alarms, catalytic combustion gas sensors are susceptible to high-temperature heat generated by high-concentration gases, and there is nothing that provides an appropriate indication of sensor deterioration after long-term use under adverse conditions. .

The present invention was developed in view of the above circumstances, and provides a gas leak alarm that protects the gas sensor from high concentration gas and also has the function of notifying the performance of the gas leak alarm due to deterioration of the gas sensor. The purpose is to provide.

Hereinafter, preferred embodiments of the present invention will be described in detail as illustrated in the accompanying drawings.

In the drawing, the bridge circuit has a catalytic combustion gas sensor 1 and a compensation element 2, the common point of which is connected to one input of three comparators 3, 4, 5. The other inputs of the comparators 3, 4, and 5 are connected to variable resistors 6, 7, and 8 of the bridge circuit, respectively. The bridge circuit also includes a transistor 9 and a resistor 10 connected in series. The base of transistor 9 is connected to the output of operational amplifier 11, and the emitter is connected to one of its inputs. The other input of the operational amplifier 11 is connected to a two-stage variable reference voltage source 12. This switching of the reference voltage source 12 is effected by a transistor 13 connected to the output of the comparator 3. The output of the comparator 4 is connected to a buzzer oscillation circuit 14 and an external output circuit 17. The output of the buzzer oscillation circuit 14 is connected to drive a buzzer 15 intermittently. Buzzer 15
and external output circuit 17 is connected to transistor 16 which is activated by the output of comparator 5. External output circuit 17 includes two Zener diodes 1
8, 19 and a control transistor 20, the output of which is connected to an external central monitoring board such as a supervisor's room.

A conventional gas leak alarm basically consists of a bridge circuit, a comparator 4, and a buzzer 15, and a variable resistor 7 for setting an alarm point causes the buzzer 15 to sound when the concentration of the gas to be detected is 0.3%, for example. adjusted to This embodiment includes a buzzer oscillation circuit 14 and an external output circuit 17, which are controlled by a comparator 4.
That is, when the gas concentration exceeds the alarm concentration and the comparator 4 switches, the buzzer oscillation circuit 14 is triggered to oscillate, causing the buzzer 15 to sound intermittently. At the same time, the external output circuit 17 outputs the voltage specified by the two Zener diodes 18 and 19 as a monitoring signal under the control of the transistor 20 when monitoring a gas leak. The voltage specified only by the voltage is output as an alarm signal.

The variable resistor 6 is used to adjust the comparator 3 to operate when the bridge circuit detects a high gas concentration, for example, 21% or more. The operational amplifier 11 acts to make the emitter voltage of the transistor 9 equal to the voltage of the reference voltage source 12, so that a constant current flows through the bridge circuit. For example, during normal gas leak standby, the sensor current is
It is set to 300mA. When a high concentration gas is detected, the comparator 3 operates, the transistor 13 becomes conductive, and the reference voltage of the reference voltage source 12 is lowered. The current flowing through the bridge circuit is therefore reduced, e.g. the sensor current is limited to 100mA,
Since the self-heating of the sensor is reduced, overheating of the sensor due to combustion heat is prevented.

The variable resistor 8 is used to set the allowable drift width of the zero point in the direction of sensitivity of the bridge circuit due to deterioration of the sensor 1. When the bridge circuit exceeds the drift width, the comparator 5 operates and the transistor 16 becomes conductive and causes the buzzer 15 to continuously sound. At the same time, the base current supplied to the base of the transistor 20 of the external output circuit 17 is completely absorbed by the transistor 16, so the transistor 20 becomes non-conductive, which means that the external output circuit 17 is malfunctioning of the gas leak alarm. Outputs a 0V voltage signal. In this preferred embodiment, the buzzer 15
The intermittent beeping is used to detect a gas leak, and the continuous beeping is used to indicate deterioration of the gas sensor 1, thereby making the alarm unit common. Further, the deterioration display of the sensor can also be reported to an external central monitoring board through the external output circuit 17.

According to the present invention, by switching the current of the gas sensor according to the detected gas concentration, self-heating of the sensor when high concentration gas is detected is reduced.
This protects the sensor from overheating even when heated by combustion heat, and at the same time, it can detect zero drift due to deterioration of the gas sensor and alert you to a decline in gas sensor performance, making it safer. A highly reliable gas leak alarm is provided.

[Brief explanation of the drawing]

The drawing is an electrical circuit diagram showing an embodiment of the gas leak alarm according to the present invention. 1... Gas sensor, 2... Compensation element, 3, 4,
5... Comparator, 6, 7, 8... Variable resistor, 12
... Reference voltage source, 14 ... Oscillation circuit, 15 ... Buzzer.

Claims (1)

[Scope of utility model registration request] A bridge circuit including a catalytic combustion gas sensor,
A comparator connected to the output of this bridge circuit,
A gas leak alarm including an alarm that sounds intermittently when the comparator detects a predetermined concentration of gas, which includes a resistor and a transistor connected in series to the bridge circuit, and a voltage drop across the resistor. an amplifier that controls the transistor so that the voltage drop caused by the current flowing through the bridge circuit becomes a first predetermined value; a high concentration protection circuit having a comparator that switches the first predetermined value to a smaller second predetermined value when the first predetermined value is reached, and a high concentration protection circuit connected to the output of the bridge circuit so that the balanced output of the bridge circuit reaches a predetermined value. The deterioration display circuit includes a deterioration display circuit having a comparator that detects the zero drift in a direction in which the sensitivity is insensitive and continuously sounds the alarm and outputs a voltage signal indicating deterioration to an external output circuit to the central monitoring panel. A gas leak alarm featuring the following.