JPS58106687A - 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 Globan 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 invention particularly relates to the detection of sensor resistance values.

A conventional example will be explained based on FIGS. 1 and 2.

First, in FIG. 1, a DC voltage 101 is supplied to a bridge circuit consisting of a sensitive body 103 and a resistor 104 of a gas sensor 102, a temperature compensation circuit 105 that provides a reference voltage, and a resistor 106, and a voltage comparison is made between the sensor output voltage S and the reference voltage r. vessel 107
It compares and warns.

108 is a heater that keeps the sensitive body 103 at a high temperature;
03 constitutes a gas sensor 108.

However, in gas leak alarms with this type of configuration, the aging characteristics under poor environmental conditions such as high temperature and high humidity include the occurrence of polarity in the resistance value of the sensing element due to the application of DC voltage, and the alarm concentration is We know that there are big changes. Also, the second
In the figure, an AC voltage 109 is applied to the sensitive element 103, divided by series resistors 110 and 111, rectified and smoothed by a diode 112 and a capacitor 113, and compared with a reference voltage, but in this circuit configuration, the AC voltage 109 fluctuates. if you did this,
There is a problem that the sensor output fluctuates proportionally and the alarm concentration changes greatly when the power supply voltage fluctuates.

The present invention provides a gas leak alarm equipped with a resistance value detection circuit of a gas sensor sensitive body that eliminates the above-mentioned changes due to direct current application and voltage fluctuations.

Hereinafter, one embodiment of the present invention will be described based on FIG.

FIG. 3 is a configuration diagram of a gas leak alarm which employs an indirect heater type gas sensor using an N-type metal oxide semiconductor or 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 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 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. Incidentally, the resistor 46 and the 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 62 changes depending on the difference between the voltage of the capacitor 6o 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. A comparator 60 compares the charging/discharging voltage C of this capacitor 66 and the output i of the error amplifier 52, and when the voltage at the 0 point is greater than i, the comparator 6o
The output of is at the N L 11 level and drives transistors 8 and 14 via resistor 10.37. At this time a
When the voltage at the point is positive, the transistor 8 is turned on and voltage is applied to the heater 24 of the gas sensor 26. At this time, the transistor 11 is supplied with a base current from the transistor 8 via the resistor 9, but because of the presence of the diode 12, there is no ONL. The diodes 12 and 13 are the bases of the transistors 11 and 14 when they are off.
It has the role of protecting the emifuta.

On the other hand, when the voltage at point a is negative, the transistor 14 is
FF L, transistor 11 is ONL, and 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. 4a to 4d show the voltage waveforms of the respective parts 鈥髙 to d during voltage stabilization in FIG. 3.

In Figure 4 a% d, A is 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. 4 shows the waveform when no averaging is performed by the capacitor 50.

In this way, since the effective voltage is stabilized and supplied to the heater of the gas sensor 26, the sensitive body 23 of the gas sensor 26 is always maintained at a stable temperature. Now, the 11th report reference level is determined by the temperature compensation circuit consisting of resistors 19 and 20 and thermistor 21 and resistor 22. Also, when this gas sensor 26 is exposed to high concentration gas, the sensitive body 23 causes thermal runaway due to self-heating and deteriorates. Therefore, when the resistance value of the sensitive body falls below a certain value, the heater voltage is turned off, and the high concentration protection level that prevents deterioration is similarly determined by the resistors 17 and 18, and the reference level setting resistor and the sensitive body 23, respectively. The resistor 26 constitutes a bridge circuit. Six AC voltages are applied to this bridge circuit, and the gas sensor output 11 alarm concentration reference and high concentration protection reference j are connected to diodes 27, 28, .
29, smoothed by resistors 30, 31, 32 and capacitors 34, 35, 36, and comparator 43.
．． 44. Since the voltage at each point j, l, and l 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 25, the sensitive element 23
The resistance value decreases, the AC voltage at one point and the rectified and smoothed output voltage Φ increase, 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 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 69 operates to drive the buzzer 63 and issue an alarm. 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 heater voltage is turned off and the resistance value of the sensitive body 23 increases, the operation is automatically restored and the above operation is repeated.

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. High status and respect
At the time of recovery, the heater voltage is gradually returned from a low voltage.

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, it is detected by the comparators 53 and 54, and 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, it will not work if the high concentration protection circuit is activated and the heater voltage is turned off.

Further, the varistor 3 and the diode 7 are for absorbing abnormal voltage such as lightning surge, and 2 is a fuse.

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

(1) The alarm concentration is stable against voltage fluctuations.

(2) The gas sensor's characteristic zero characteristics can be maintained even under poor environments such as high temperature and high humidity, and the alarm accuracy is good.

[Brief explanation of the drawing]

1 and 2 are circuit diagrams of a conventional gas leak alarm, respectively, FIG. 3 is a circuit diagram showing an embodiment of a gas leak alarm according to the present invention, and FIG. 4a. b, c, and d are voltage waveform diagrams at various parts in FIG. 3. 17.18...Resistance network that determines the high concentration protection start level, 19, 20, 21.22...Resistance network (resistance, thermistor) that determines the alarm start gas concentration, 23.
・・Sensitive body, 24・Ki・-selfφ heater, 25II
...Gas sensor, 26.0...Resistance, 27.2
B, 29... Diode, 30, 31.32.
Life...smoothing resistance, 34, 35.36...
Smoothing condensate? , 43, 44... comparator.

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 value changes depending on the presence of flammable gas. A resistor network is connected in series with the body, and a resistor network that determines the alarm start gas concentration and a resistor network that determines the high concentration protection start level to prevent deterioration of the sensitive body due to high concentration gas are connected in parallel to form a bridge circuit. , an alternating voltage is applied to both ends of this bridge circuit, a diode is connected to the connection point between the sensitive body and the resistor, and a reference point of each of the resistor networks, and a resistor and a capacitor are connected in parallel for smoothing. A gas leak alarm device that starts an alarm or protection by comparing smoothed outputs with a comparator.