JPS6059638B2 - Abnormality detection alarm device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in an abnormality detection and alarm device that detects an abnormality such as a gas leak and generates an alarm signal.

Various devices have been proposed to detect abnormalities such as gas leaks and issue alarms, but most of these devices use DC amplifiers and therefore require offset adjustment. Further, there are drawbacks such as requiring time for adjustment, and furthermore, the gas concentration to be alarmed may deviate greatly due to adjustment errors or the like, and the alarm may not be issued even if the alarm limit is exceeded.

Also, a variable resistor is used for offset adjustment, but this variable resistor has problems with its aging characteristics, impact resistance, gas resistance, etc., and to solve these problems, a sealed variable resistor is used. This also had drawbacks, such as increasing costs. The present invention has been made to solve the above-mentioned drawbacks in the prior art, and one embodiment thereof will be described in detail below with reference to the drawings.

In FIG. 1, reference numeral 1 denotes, for example, a commercial AC power source, and its output voltage (see FIG. 2a) is applied between the anode and cathode of a thyristor 6 through an alarm 7 such as a buzzer.

Further, the voltage of this single AC power source is stepped down to a desired voltage through a transformer 2 and supplied to a full-wave rectifier circuit 3 and an AC bridge circuit 4. The output voltage of the full-wave rectifier circuit 3 is used as a power source for the operational amplifier 5, and is divided by resistors R1 and R2 and supplied to one input terminal of the inverting operational amplifier 5. On the other hand, the AC bridge circuit 4 includes at least one side thereof a gas sensing element D whose electrical resistance changes when it comes into contact with a flammable gas such as gas, and the other side thereof is used for temperature compensation of the gas sensing element D. Element C
is connected. This AC bridge circuit 4 is unbalanced when there is no flammable gas in the air, that is, under normal conditions, and becomes balanced when the concentration of flammable gas in the air reaches a set alarm concentration, and its output voltage becomes zero. The structure is such that the phase is inverted by 180 as the signal becomes larger. The output signal from the AC bridge circuit 4 is supplied to the other input terminal of the operational amplifier 5 through the DC blocking capacitor C1, but one output terminal of the AC bridge circuit 4 is connected to the connection point between the resistors R1 and R2. Since the potential is held in common with the potential, the input signal to the operational amplifier 5 increases or decreases around the reference potential divided by the resistors R1 and R2. Therefore, when the AC bridge circuit 4 is not balanced, the input signal to the operational amplifier 5 has a signal waveform as shown in FIG. 2c, and when the equilibrium point is passed, the signal waveform becomes as shown in FIG. 2d. Therefore, the output signals of the operational amplifier 5 are shown in FIG. 2 e and f, respectively.
It becomes as shown in . When the output signal voltage of the operational amplifier 5 is divided by resistors R3 and R4 and the divided voltage is applied to the control electrode of the thyristor 6, the thyristor 6 is made conductive under normal conditions and conductive only during abnormal conditions to generate an alarm. Activate device 7. Note that capacitors C2 and C3 are noise removal capacitors. c The present invention operates as described above, but since the full-wave rectified output of the full-wave rectifier 3 is used as the power source for the operational amplifier 5, the power supply voltage temporarily becomes zero. A point appears (Fig. 2G)
(See point A), the operational amplifier operates in the shaded area including this part.
At this point, a whisker appears on the output of the operational amplifier (see E and fB in FIG. 2). As a countermeasure for this, conventionally,
Although the gate bias voltage of the thyristor was determined by appropriately selecting the division ratio between the resistors R3 and R, the gate voltage of the thyristor 6 could still not be accurately controlled. The main purpose of the present invention is to eliminate the influence of this whisker, and the differential capacitor C shown in FIG. 1 is inserted to eliminate the influence of this whisker. By inserting C, the influence of the whiskers can be effectively removed, and furthermore, the resistance ratio of resistors R3 and R, and the tolerance of the variation in each resistance value can be increased. There are effects such as being able to. As is clear from the above description, according to the present invention, since an operational amplifier is used as an AC amplifier,
There is no need for offset adjustment, therefore, the time required for offset adjustment is unnecessary and there is no inconvenience, and there is no risk of malfunction due to an error in offset adjustment.

In addition, since there is no need for a variable resistor for offset adjustment, there is an advantage of being freed from various measures such as aging characteristics, impact resistance, gas resistance, etc. of variable resistors for offset adjustment, which have had many problems in the past. . Furthermore, with a simple configuration, the gate bias voltage of the thyristor can be set accurately, and an abnormality detection and alarm device with fewer malfunctions can be provided.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram for explaining an embodiment of the present invention, and FIG. 2 is an electric signal waveform diagram for explaining the operation of the present invention. 1... AC power supply, 2... Transformer, 3.
... Rectifier circuit, 4 ... AC bridge circuit, 5 ... Operational amplifier, 6 ... Thyristor,
7... Alarm device, C,... DC blocking capacitor, C,... Differential capacitor.

Claims (1)

[Claims] 1 an AC power supply circuit, a full-wave rectifier circuit for full-wave rectification of an AC voltage from the AC power supply circuit, an AC bridge circuit powered by the AC voltage from the AC power supply and including a detection element on at least one side; an operational amplifier that uses the full-wave rectified voltage from the full-wave rectifier circuit as a power source and uses the output signal from the AC bridge circuit as an input signal through a DC blocking capacitor; and a differential capacitor connected to the output side of the operational amplifier. and a thyristor that uses an AC voltage from the AC power source as a power source and uses an output signal from the operational amplifier as a control signal through the differential capacitor, and when an abnormality occurs,
An abnormality detection and alarm device characterized in that when the phase of the output signal voltage of the AC bridge circuit is inverted by 180°, the thyristor is made conductive to activate an alarm.