JPS58106685A - Gas leakage alarm - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] The present invention relates to a gas leak alarm.

BACKGROUND ART In recent years, with the increase in the usage of propane gas and city gas, the scale of accidents caused by gas leaks such as explosions has become larger, and efforts are being made in various fields to prevent gas leak accidents. Among them, gas leak alarms are attracting attention as the last line of defense against accidents, and efforts are being made to popularize them.

The present invention aims to further improve the performance and reliability of a gas leak alarm that has the above-mentioned important mission. The present invention particularly relates to stabilizing the heater voltage of a gas sensor.

A conventional example will be explained based on FIGS. 1 to 3.

First, in FIG. 1, an AC voltage is supplied from a power supply 101 to a power transformer 102, and the output voltage of the transformer 102 is rectified by a diode bridge 103 and smoothed by a capacitor 104, and then a series regulator 105 is configured by a sensing element 106 and a heater 107. This is to stabilize the voltage of the heater 107 of the gas sensor 108 as a direct current. This method has the following drawbacks.

(1) Considering power supply voltage fluctuations, the series regulator 105 has a large power loss and heat generation.

(2> From (1) above, the series regulator 106
A heat dissipation plate, etc. is required, making the structure complex and the shape large.

(3) In addition to power loss, since it is converted to DC, the output current of the transformer 102 flows concentrated near the peak voltage, and other transformer outputs become ineffective, resulting in poor efficiency and large transformer 102. It becomes necessary.

In addition, in FIG. 2, a commercial power supply 101 is directly rectified by a diode bridge 103, then switched by a switching circuit 109, and voltage converted by a high frequency transformer 110.
This method uses a diode 111 and a capacitor 112 to convert the voltage into a DC voltage, and although this method has good efficiency and is small and lightweight, it has the following drawbacks.

(1) It is necessary to use ferrite or the like for the core of the high frequency transformer 110, which increases the cost.

(2) Noise from the switching circuit 109 enters the AM band of the radio receiver and radio equipment, necessitating a shield, which complicates the construction method and shape.

Finally, as shown in Fig. 3, although the efficiency is good because the control is performed using AC voltage, the peak voltage of AC voltage is controlled by the constant current circuit 113.
The alarm concentration is only clipped at the voltage, and does not correspond to the effective voltage of the heater 107, so the error is large, and the voltage dependence of the alarm concentration is large.

The present invention provides a gas leak alarm equipped with a gas sensor heater voltage stabilizing circuit that is free from the problems of the conventional examples.

Hereinafter, one embodiment of the present invention will be described based on FIG. FIG. 4 is a configuration diagram of a gas leak alarm that employs an indirect heater type gas sensor using an N-type metal oxide semiconductor (iron oxide complex oxide semiconductor) as a sensitive body. Now, when the power supply 1 is turned on, an AC voltage is applied to the diode bridge 6 from the output of the power transformer 4, and the DC voltage is rectified by the diode bridge 5 and smoothed by the capacitor 6, and is supplied to the circuit. This DC voltage is stabilized by a stabilizing circuit 40. At this time, the capacitor 4
8, a timer (hereinafter referred to as the initial timer) that prevents an initial alarm due to a decrease in resistance value that occurs when the gas sensor 26 is initially energized operates until the comparator 49 is inverted. 62 blinks by the oscillation circuit 67 and the LED drive circuit 58 to indicate that the initial timer is in operation, but the alarm buzzer 63 does not operate. Then, when the capacitor 48 is charged and the comparator 49 becomes negative, the initial timer ends and a normal monitoring state is entered. Note that the resistor 46 and diode 46 are used to determine the time for discharging the charge in the capacitor 48 when the power is turned off.

On the other hand, when the power source 1 is turned on, AC voltage is also supplied to the secondary side point a of the transformer 4, and the voltage of the heater 24 is changed to the resistor 33a.
.

The output of this error amplifier 52 changes depending on the difference between the voltage of the capacitor 50 and the reference voltage f. Also, the AC voltage at point a above is divided by resistor 15.16, and capacitor 3
When the input AC signal passes through zero, this zero cross circuit 41 sets the output to 0, discharges the voltage of the capacitor 66, and then the capacitor 56 receives the stabilizing signal. It is charged from a power source via a resistor 65. A comparator 60 compares the charging/discharging voltage C of the capacitor 56 and the output i of the error amplifier 52, and when the voltage at the 0 point is greater than i, the comparator 6
The output of 0 becomes "L" level and drives transistors 8 and 14 via resistor 10.37. At this time, when the voltage at point a is positive, the transistor 8 is turned on and a voltage is applied to the heater 24 of the gas sensor 26. At this time, the transistor 11 is supplied with the base current from the transistor 8 via the resistor 9, but since the diode 12 is present, the base current is supplied from the transistor 8 through the resistor 9.
No N. The diode 12 and the diode 13 have the role of protecting the base and emitter of the transistors 11 and 14 when they are turned off. On the other hand, when the voltage at point a is negative, the transistor 14 is turned off, the transistor 11 is turned on, and a voltage is applied so that point d of the heater 24 becomes negative. In this way, each circuit operates to keep the root mean square of the heater voltage constant, and the effective value of the voltage of the heater 24,
In other words, it is a phase-controlled voltage stabilizing circuit that keeps the power constant. FIGS. 6a to 6d show voltage waveforms at each part a to d during voltage stabilization in FIG. 42. 6th
In Figures a to d, A indicates a case where the power supply voltage is high and a case where the power supply voltage is low, and a shaded area indicates a case where voltage is applied to the heater 24. Note that the diagram at point b in FIG. 6 shows the waveform when no averaging is performed by the capacitor 60.

Since the effective voltage is stabilized and supplied to the heater 24 of the gas sensor 25 in this way, the sensing element 2 of the gas sensor 26
3 is always maintained at a stable temperature.

Now, the alarm standard level is resistance 19.20 and thermistor 21
It is determined by the temperature compensation circuit and the resistor 22, and if the gas sensor 26 is exposed to a high concentration of gas, the sensing element 23 may cause thermal runaway due to self-heating and deteriorate, so the resistance value of the sensing element must be below a certain value. When the voltage is reached, the heater voltage is turned off,
A high concentration protection level to prevent deterioration is also provided by a resistor of 17.1
8, each reference level setting resistor and sensitive body 2
3 and the resistor 26 constitute a bridge circuit. Although the AC voltage at point d is applied to this bridge circuit, the gas sensor output 2. The alarm concentration reference k and the high concentration protection reference j are rectified by diodes 27, 28, and 29, and each resistor 30.
, 31.32 and capacitors 34°, 35.36, and are input to comparators 43 and 44. j, ni, fl
Since the voltage at each point is an AC voltage, it does not change due to fluctuations in the power supply voltage because it is a bridge circuit.

Now, when combustible gas touches the gas sensor 26, the sensitive element 23
The resistance value decreases, the AC voltage at the two points and the rectified and smoothed output voltage δ rise, and when they exceed the alarm reference voltage output n, the comparator 44 is inverted, activating the oscillation circuit 57 and the LED drive circuit 58, The LED 62 starts blinking, activates the delay timer circuit 61, and changes the external output circuit 64 from the normal state of about 6V to the gas detection state of 12V or more and outputs the output. When the operation of the delay timer circuit 61 is completed, the buzzer drive circuit 59 operates and drives the buzzer 63.
Alert. Here, the delay timer circuit 61 is a timer for reducing false alarms due to temporary gas.

Furthermore, when the gas concentration increases and the voltage at the 6 points becomes higher than the voltage at the m point of the high concentration protection standard, the comparator 43 is reversed, the operation of the comparator 60 for controlling the heater voltage is stopped, and the heater voltage is turned off. To prevent deterioration of the body 23. Then, when the resistance value of the sensitive body 23 increases due to the heater voltage being turned off, the system automatically returns to normal operation and repeats the above operation.

In addition, since the heater voltage is low in the high concentration protection state, a high voltage is applied to the heater voltage upon recovery.As a countermeasure, when the high concentration protection circuit is operating, the output of the square circuit 42 is lowered by a resistor 51 to reduce the heater voltage. is set equal to the high state, and the heater voltage is made to gradually return from a low voltage at the time of recovery.

Now, if an abnormality such as a failure occurs in the heater voltage control system, it cannot be expected to function normally as a gas leak alarm, and in this alarm, the heater control system has a large current and there is a possibility of failure. The voltage at the output point i of the error amplifier 52 is q
, h, if the voltage exceeds the voltage range set by
, turn off the LED 62 to notify the failure. This circuit works even if the power supply voltage drops abnormally and the heater voltage stabilization circuit is normal but does not reach the reference voltage. However, if the high concentration protection circuit is activated and the heater voltage is turned off, it will not move.

The varistor 3 and diode 7 are for absorbing abnormal voltages such as lightning surges, and 2 is a fuse.

Here, in the temperature compensation shown in the conventional example, the heater voltage is kept constant with respect to the temperature, and the temperature dependence of the resistance value of the sensitive body is compensated for by giving a temperature characteristic to the reference level of the alarm concentration. The temperature dependence of resistance value is large for methane,
Since the value varies depending on the type of combustible gas, such as hydrogen and isobutane having a small value, it is necessary to set a central value. As is clear from this, the temperature characteristics vary depending on the type of gas.

Therefore, by giving temperature dependence to the dividing resistor 33a of the heater voltage detection circuit or giving temperature characteristics to the reference voltage f, the temperature of the sensitive body 23 becomes constant regardless of the external temperature, and the temperature dependence of the sensitive body 23 becomes constant regardless of the external temperature. Therefore, there is no variation in temperature characteristics depending on the type of gas as in the conventional example. Additionally, characteristics such as response time do not change accordingly, and a history after temperature change is less likely to occur and recovery is quick.

The present invention is constructed as described above, and has the following effects.

(1) Since the heater voltage is stabilized with alternating current, the transformer has good efficiency and can be configured to be small and inexpensive.

(2) This is AC effective value control, which corresponds to the amount of heat generated.
The configuration is such that the amount of change in alarm concentration with respect to power supply voltage fluctuations is small.

[Brief explanation of the drawing]

1 to 3 are circuit diagrams of conventional gas leak alarms, FIG. 4 is a circuit diagram showing an embodiment of the gas leak alarm according to the present invention, and FIG. 6a. b, c, and d are voltage waveform diagrams at each part in FIG. 4. 11.14... Switching element (transistor), 23... Sensing body, 24... e... Heater, 25... e... Gas sensor, 42... Kensan00 multiplier (square circuit), 50, 56...0.・, capacitor,
52 mass...Error amplification device.

Claims (1)

[Claims] (1) The resistance value changes due to the presence of flammable gas.
The gas concentration is determined and alarmed based on a change in the resistance value of a sensitive body made of an N-type metal oxide semiconductor kept at a high temperature by a heater. or the square of the heater current, or the product of the heater voltage and heater current, using a multiplier, smoothing and averaging the output of this multiplier using a capacitor, and making sure that this average value is equal to the set reference voltage. A gas leak alarm, characterized in that the effective value of the heater voltage is stabilized by controlling the switching element. ? ) The difference between the output of the multiplier and the reference voltage is amplified by an error amplifier, and the output of this error amplifier is compared with the capacitor voltage that is discharged synchronously when the AC voltage is zero volts and then charged. The switching element is opened and closed by
A gas leak alarm according to claim 1, comprising a heater voltage effective value stabilizing circuit configured to perform phase control. (1) The invention includes a heater voltage stabilizing circuit that is capable of compensating for the temperature dependence of the sensitive body by giving the reference voltage of the heater voltage control circuit or the heater voltage detection circuit a temperature characteristic. Gas leak alarm.