JPS6059639B2 - 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. There were drawbacks such as requiring time for adjustment, and furthermore, the gas concentration to be alarmed may deviate greatly due to adjustment errors, and the alarm may not be issued even if the alarm limit is exceeded.

In addition, a variable resistor is used for offset adjustment, but there are problems with the aging characteristics, impact resistance, gas resistance, etc. of this variable resistor, and to solve these problems, a sealed variable resistor is used. However, there were drawbacks such as this leading to an increase in 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, 1 is, for example, a commercial AC power supply, and its output voltage (second
(see figure a) is connected to the thyristor 6 through an alarm device 7 such as a buzzer.
It is added between the anode and cathode.

Further, the voltage of this AC power supply 1 is stepped down to a desired voltage through a transformer 2 and is 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 connected to a resistor R.
1 and R2 and is supplied to one input terminal of the inverting operational amplifier 5. On the other hand, the AC bridge circuit 4 includes a gas sensing element D whose electrical resistance changes when it comes into contact with flammable gas such as gas on at least one side, and temperature compensation of the gas sensing element D on the other side. 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 is approximately The structure is such that the phase is reversed by 180 when the force becomes zero.
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. The input signal to the operational amplifier 5 increases or decreases around the reference potential divided by the resistors R 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,
When the equilibrium point is passed, the signal waveform becomes as shown in FIG. 2d, and the . The output signals are as shown in FIGS. 2e and f, respectively. 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, causing an alarm. Operate 7. Note that capacitors C2 and C3 are noise removal capacitors. 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, there is a point where the power supply voltage temporarily becomes zero. occurs (see point G..A in Figure 2), and the operational amplifier becomes inoperable in the shaded area that includes this part, and at this point, the output of the operational amplifier has a whisker (see E, f, B in Figure 2).
coming out.

Conventionally, as a countermeasure for this problem, the gate bias voltage of the thyristor was determined by appropriately selecting the division ratio of the resistors R3 and R4, but even then, the gate voltage of the thyristor 6 could not be accurately controlled. The main purpose of the present invention is to remove this whisker, and the smoothing capacitor C5 shown in FIG. 1 is inserted to remove this whisker. When this smoothing capacitor C5 is inserted to smooth the output voltage of the rectifier circuit 3, a voltage higher than the specified voltage is always applied to the operational amplifier 5, so that there is no band in which the operational amplifier 5 is inactive, and the whisker does not appear. Furthermore, by inserting a differential capacitor C in addition to the smoothing capacitor q on the output side of the operational amplifier 5, malfunction of the thyristor due to phase delay can be eliminated.
There are effects such as being able to increase the ratio of the four resistances and the tolerance of variation in each resistance value. As is clear from the above description, according to the present invention, since an operational amplifier is used as an AC amplifier, offset adjustment is not necessary. Therefore, the time required for offset adjustment is unnecessary and the troublesomeness thereof is eliminated. Moreover, there is no risk of malfunction due to incorrect 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, the non-operating band of the operational amplifier can be effectively removed with a simple configuration, and a highly reliable abnormality detection and alarm device 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, C1 ... DC blocking capacitor, C4... Differential capacitor, C5...
...Smoothing capacitor.

Claims (1)

[Scope of Claims] 1. An AC power supply circuit, a rectifier circuit for rectifying the AC voltage from the AC power supply circuit, a smoothing circuit for smoothing the output voltage of the rectification circuit, and an AC power supply circuit for rectifying the AC voltage from the AC power supply circuit. an AC bridge circuit that uses a voltage as a power source and includes a detection element on at least one side; and an operational amplifier that uses a smoothed DC voltage from the smoothing circuit as a power source and uses an output signal from the AC bridge circuit as an input signal through a DC component blocking capacitor. , a thyristor whose power supply is an AC voltage from the AC power supply and whose control signal is an output signal from the operational amplifier, and when an abnormality occurs, the phase of the output signal voltage of the AC bridge circuit is 1.
An abnormality detection and alarm device characterized in that when the thyristor is reversed by 80 degrees, the thyristor is made conductive to generate an alarm signal. 2. An AC power supply circuit, a rectification circuit for rectifying the AC voltage from the AC power supply circuit, a smoothing circuit for smoothing the output voltage of the rectification circuit, and at least one side using the AC voltage from the AC power supply as a power source. an AC bridge circuit including a detection element; an operational amplifier that uses the smoothed DC voltage from the smoothing circuit as a power source and uses an output signal from the AC bridge circuit as an input signal through a DC blocking capacitor; and an output of the operational amplifier. The differential capacitor connected to the side,
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, the phase of the output signal voltage of the AC bridge circuit is reversed by 180 degrees. An abnormality detection and alarm device, characterized in that when the thyristor is turned on, an alarm signal is generated.