JPS58106686A - 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.

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 increased, 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, the output voltage of the transformer 102 is rectified by a diode bridging 103, smoothed by a capacitor 104, and then a series regulator 105 is connected to a sensitive body 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 the above (1), a heat sink etc. of the series regulator 105 is required, making the structure complicated and the shape large.

(3) In addition to power loss, transformer 1
The output current of 02 flows in a concentrated manner near the peak voltage, and other transformer outputs become ineffective, resulting in poor efficiency and requiring a large transformer 102.

In addition, in Fig. 2, the commercial power supply 101 is directly connected to a diode
After rectifying in the transformer 103, switching in the switching circuit 109, and converting the voltage in the 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 an F element condition.

(1) It is necessary to use ferrite etc. for the core of the high frequency transformer 110, which is expensive and expensive for many companies.
The noise of the switching circuit 109 is the AM of the radio receiver.
band, radio equipment, shielding is required, construction method,
The shape becomes complicated.

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.
Since the voltage is only bridged by the voltage and does not correspond to the effective voltage of the heater 107 and the error is large, the dependence of the alarm concentration on the voltage is large.

The present invention provides a gas leak alarm equipped with a heater voltage stabilizing circuit for a gas sensor, which is free from the problems of the conventional example described above.

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 5 from the output of the power transformer 4, rectified by the diode bridge 6, and DC voltage smoothed by the capacitor 6 is supplied to the circuit. This DC voltage is stabilized by a stabilizing circuit 4o. 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. The oscillation circuit 67 and the LED drive blink at 68 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 is inverted, the initial timer ends and a normal monitoring state is entered. Note that the resistor 45 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 is divided by resistor 15.16, and capacitor 38
When the input AC signal passes through zero, this zero cross circuit 41 sets the output to 0 and discharges the voltage of the capacitor 66.
Thereafter, the capacitor 66 is charged from the stabilized power supply via the resistor 56. The voltage C charging and discharging this capacitor 66 and the output i of the error amplifier 52 are compared by the comparator 60, and when the voltage at the 0 point is greater than i, the comparator 6
The output of o becomes L'' level and drives PNP transistors 8 and 14 via resistor 10.37. At this time, when the voltage at point a is positive, transistor 8 turns on,
A voltage is applied to the heater 24 of the gas sensor 25. At this time, the NPN transistor 11 is supplied with base current from the transistor 8 via the resistor 9, but the diode 12
It does not turn on because of this. The diode 12 and the diode 13 have the role of protecting the base and emitter of the transistor 11.14 when it is OFF. on the other hand,
When the voltage at point a is negative, transistor 14 is turned off, transistor 11 is turned on, and a voltage is applied so that point d of heater 24 becomes negative. In this way, each circuit operates to keep the root mean square of the heater voltage constant, forming a phase control type voltage stabilizing circuit that keeps the effective voltage value of the heater 24, that is, the power constant. FIGS. 6a to 6d show voltage waveforms at each part a to d during voltage stabilization in FIG. 4. In FIGS. 5a to 5d, A is the case when the power supply voltage is high and the opening is low, and the shaded area is the heater 24.
This is the case when a voltage is applied to .

Note that the diagram at point b in FIG. 6 shows the waveform when no averaging is performed by the capacitor 60.

Since the dynamic voltage is stabilized and supplied, the sensitive body 23 of the gas sensor 26 is always maintained at a stable temperature. If the gas sensor 25 is exposed to a high concentration of gas, the sensitive body 23 may cause thermal runaway due to self-heating and deteriorate. Therefore, when the sensitive body resistance value falls below a certain value, the heater voltage is turned off to prevent deterioration. The high-concentration protection level for preventing this is similarly determined by resistors 17 and 18, and the respective reference level setting resistors, the sensitive body 23, and the resistor 26 constitute a bridge circuit. The AC voltage at point a is applied to this bridge circuit, but the gas sensor output l
, alarm concentration reference and high concentration protection reference j are rectified by diodes 27, 28, 29 and resistors 30, 3, respectively.
1.32 and capacitors 34, 35, and 36, and are input to comparators 43 and 44. Since the voltage at each point j, 7 is a bridge circuit, although it is an alternating voltage, it does not change due to fluctuations in the power supply voltage.

Now, when combustible gas touches the gas sensor 26, the sensitive element 23
The resistance value decreases, the AC voltage at one point and the rectified and smoothed output voltage δ rise, and when it exceeds the alarm reference voltage output n, the comparator 44 is inverted, activating the oscillation circuit 57 and the LED drive circuit 68, The LED 62 starts blinking, activates the delay timer circuit 61, and changes the external output circuit 64 from a normal state of about 6V to a gas detection state of 12V or more. 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 0 point 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.

Since the heater voltage is low in the concentration protection state, a high voltage is applied to the heater voltage when it returns to normal.As a countermeasure, when the high concentration protection circuit is activated, the output of the 2nd east circuit 42 is lowered by the resistor 51, and the heater voltage is lowered. The voltage is set equal to the high voltage state, and the heater voltage gradually returns from a low voltage upon 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 62 is g
, h, it is detected by the comparators 53 and 64, the LED drive circuit 58 is turned off, the LED 62 is turned off, and a malfunction is notified. 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 be activated.

The varistor 3 and the diode 7 are for absorbing abnormal voltages such as lightning surges, and 2 is a fuse -1A~ The present invention is constructed as described above, and has the following effects. .

(1) Since alternating current stabilization of the heater voltage is performed using a transistor, a diode is not required when the input heater voltage is low, resulting in low saturation voltage and high efficiency.

(21) Since the switching speed of the i-register is slow, no noise is generated in radio receivers and radio equipment.

(3) Since transistors are used for switching, small and inexpensive transistors can be used.

[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 various parts in FIG. 4. 8...Second P N P, ) transistor, 9
...Resistance, 10...Resistance, 11...
...NrN transistor, 12.13...
Diode, 14...first PNP) transistor, 23...sensor, 24...heater, 25...gas sensor, 37... ·resistance. ′

Claims (1)

[Claims] The gas concentration is determined by the change in resistance of a sensitive body made of an N-type metal oxide semiconductor kept at a high temperature by a heater, and the resistance changes depending on the presence of flammable gas. is connected to the ground line, and the collectors of the first PNP transistor and NPN transistor are connected to the other end of this heater, respectively.
The base of the transistor is connected via a resistor to the collector of a second PNP transistor whose emitter is connected to a sufficiently high DC positive voltage power supply, and the first PNP transistor and the L-mitter of the NPN transistor are connected directly or The base and emitter are connected through diodes connected in the forward direction, and an AC voltage for the heater voltage is applied between this connection point and the ground line, and the first PNP transistor and the second A gas leak alarm having an AC heater voltage control circuit that drives the bases of the transistors with phase control signals that serve as ground lines through resistors.