JPH0544924A - Safety valve control circuit for gas instrument - Google Patents

Abstract

PURPOSE:To interrupt gas without fail by closing a safety valve even when such a trouble occurs as cannot turn OFF a relay contact inserted between a thermocouple and the safety valve. CONSTITUTION:A safety valve control circuit for gas instrument is provided with a trouble detecting circuit 4 to detect such a trouble as cannot turn OFF a relay contact 3a, and an inverse voltage impressing circuit 5 which, when a trouble is detected out, closes a safety valve 2 by impressing on the safety valve 2 a voltage of an inverse polaliry to heat electromotive force of a thermocouple 1. Accordingly, even when a trouble occurs in a relay, its contact or a circuit relating to them, the safety valve can be closed to interrupt gas without fail.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a safety valve control circuit for a gas appliance in which a safety valve is reliably closed when a contact or the like provided for closing the safety valve fails.

[0002]

2. Description of the Related Art It is well known that a device such as a gas stove which holds a safety valve in an open state by a thermoelectromotive force of a thermocouple and automatically closes a gas by closing the safety valve when time is up. is there. This automatic fire extinguishing is generally performed by turning off the relay contact inserted between the thermocouple and the safety valve.However, in such a configuration, for example, a failure such that the contact cannot be turned off, such as a short-circuit of the contact. If a fire occurs, the safety valve will remain open, and it will not be possible to shut off the gas and automatically extinguish the fire.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of such a point, and has an object to surely shut off a gas by closing a safety valve even when a failure occurs in which a contact cannot be turned off. It is a thing.

[0004]

In order to achieve the above object, according to the present invention, a failure detecting circuit for detecting a failure in a state where a relay contact cannot be turned off, and the failure detecting circuit detects the above failure. And a reverse voltage application circuit that applies a voltage having a polarity opposite to that of the thermoelectromotive force of the thermocouple (hereinafter referred to as a reverse voltage) to the safety valve to close the safety valve. FIG. 1 is a basic circuit diagram showing the configuration of the present invention, in which 1 is a thermocouple, 2 is a safety valve, 3 is a relay, 3a is its contact point, 4 is a failure detection circuit, 5 is a reverse voltage application circuit, and 6 is a control unit. Is.

[0005]

In FIG. 1, the contact 3a is ON during the combustion of gas, the electric current due to the thermoelectromotive force of the thermocouple 1 flows in the direction of the broken line arrow, and the safety valve 2 is excited and held in the open state. ing. When the fire is extinguished, the relay 3 is activated by the control signal output from the control unit 6 to turn off the contact 3a. Before that, the failure detection circuit 4 causes the relay 3 and its contact 3
The failure state of a is detected, and if there is a failure, the reverse voltage application circuit 5 is operated to apply the reverse voltage in the direction of the solid arrow. As a result, the thermoelectromotive force of the thermocouple 1 is canceled, and the safety valve 2 can no longer maintain the open state and is closed, so that the gas is shut off.

[0006]

EXAMPLE Next, an example shown in FIG. 2 will be described.
The same parts as those in FIG. 1 are designated by the same reference numerals. In the figure, Q1 is an operation detection transistor of the relay 3, R
1 and R2 are their base and pull-up resistors, T1
Is an on / off detection terminal of the transistor Q1, Q2 is a transistor for applying a reverse voltage to the safety valve 2, R3 is a base resistance thereof, R6 is a current limiting resistance of reverse voltage, and T2 is a drive signal terminal of the transistor Q2. Q3 is a transistor Q
2 failure detection transistors, R4 and R5 are base resistance and pull-up resistance thereof, T3 is an ON / OFF detection terminal of the transistor Q3, Q4 is a drive transistor of the relay 3, R7 is its base resistance, T4 is a drive signal of the transistor Q4. The terminal D1 is a diode for absorbing the back electromotive force of the relay 3, and Vcc1 and Vcc2 are DC power supplies.

Most of these circuits are mounted on a printed circuit board and connected as shown in the drawing, and the wiring portions A, B, C and D shown by double lines are constituted by harnesses. Further, the contact 3a of the relay 3 has a normally closed (NC) side and a normally open (NO) side, and when the relay 3 is not driven, it is switched to the normally closed side as shown in the figure, and the thermocouple 1 and the safety valve 2 are connected. Are connected to each other. The main part of the control unit 6 is composed of a microcomputer, and a program is set to perform the following operations.

This embodiment has the structure as described above,
It works as follows. This operation is roughly classified into an initial check operation and an operation at time-up. In the initial check, a relay-related check and a reverse voltage application circuit check are performed.

First, a drive signal is output from the control unit 6 to the terminal T4, the transistor Q4 is turned on, the relay 3 is activated, and the contact 3a is switched to the normally open side. Since the base current supplied to the transistor Q1 through the resistor R1 is grounded to GND through the safety valve 2, the transistor Q1 is turned off and the signal level at the terminal T1 changes from L to H.
become. Here, when the contact Qa does not switch to the normally open side due to an abnormality such as disconnection in the circuit including the transistor Q4, the relay 3 and the harness wiring parts C and D, or the contact 3a itself has a failure such as a short circuit. If it does not switch to the normally open side, the transistor Q1 does not turn off, the signal level of the terminal T1 remains L, and there is a relay-related failure in which the contact 3a cannot be turned off. It is detected by the control unit 6 depending on the state.

Subsequently, a drive signal is output from the control section 6 to the terminal T2, the transistor Q2 is turned on, and the DC power supply V
The voltage of cc1 is applied to the safety valve 2 through the harness wiring portion A, but since this voltage is grounded to GND via the safety valve 2, the base current of the transistor Q3 does not flow through the resistor R4 and the transistor Q3 remains off. The signal level of the terminal T3 remains H. However, the harness wiring part A
If the voltage of the DC power source Vcc1 is not applied to the safety valve 2 due to a disconnection in the transistor, the transistor Q3 is connected through the resistor R4.
Since the base current is supplied to the transistor Q3, the transistor Q3 is turned on and the signal level at the terminal T3 becomes L. That is,
The control unit 6 detects whether or not there is a failure in the reverse voltage application circuit based on the signal level at the terminal T3. If there is no abnormality as a result of the above checks, cooking can be started, for example, combustion is performed until the timer built in the control unit 6 times up, during which the safety valve 2 is excited by the thermoelectromotive force of the thermocouple 1 and opened. Held in a state.

Next, at the time when the cooking is finished, the control unit 6 outputs a drive signal to the terminal T4, and the transistor Q
4 is turned on to activate the relay 3. If the relay contact 3a does not switch to the normally open side, the transistor Q1 does not turn off and the signal level at the terminal T1 becomes L as described above.
When the control unit 6 detects this, it judges that it is a relay-related failure, outputs a drive signal from the terminal T2, turns on the transistor Q2, and applies the voltage of the DC power supply Vcc1 to the safety valve 2. .. This voltage has a polarity opposite to that of the thermoelectromotive force of the thermocouple 1, and by appropriately selecting the value of the resistor R6, the thermoelectromotive force of the thermocouple 1 is canceled by this voltage, the safety valve 2 is closed, and the gas is closed. Is cut off.

In this way, when an abnormality is detected in the relay contact 3a or its related circuit, the reverse voltage is applied to close the safety valve 2 and reliably shut off the gas. Further, in this embodiment, since the relay relation and the initial check of the reverse voltage application circuit are also performed at the initial stage of the operation of the device, the fail-safe property at the time of failure is further improved. In this embodiment, the relay 3 is not driven during combustion, and the safety valve 2 is connected to the thermocouple 1 through a normally-closed contact generally called B contact.
The relay 3 is driven to turn off the contact when the gas is cut off. This is because a small gas stove or the like often uses a dry battery as a power source for control, and it is necessary to reduce power consumption of the dry battery. This invention connects a safety valve to a thermocouple through an A contact. It can also be applied to the system type.

[0013]

As is apparent from the above-described embodiments, the present invention is provided with a failure detection circuit for detecting a failure in a state in which the relay contact cannot be turned off, and when a failure is detected, a reverse voltage application circuit is used to provide a safety valve. The safety valve is closed by applying a reverse voltage. Therefore, even if there is a failure in the relay, its contact point, or a circuit related thereto, the safety valve can be closed to reliably shut off the gas, and the safety can be improved by the fail-safe operation.

[Brief description of drawings]

FIG. 1 is a basic circuit diagram showing the configuration of the present invention.

FIG. 2 is a circuit diagram of an embodiment of the present invention.

[Explanation of symbols]

 1 Thermocouple 2 Safety valve 3 Relay 3a Relay contact 4 Failure detection circuit 5 Reverse voltage application circuit 6 Control part Q1, Q2, Q3, Q4 Transistor A, B, C, D Harness wiring part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Takabayashi 1-152 Oka, Minamiichi, Minato-ku, Osaka City Harman Co., Ltd.

Claims (1)

[Claims] 1. A safety valve is kept open by thermoelectromotive force of a thermocouple, and a safety contact is closed by turning off a relay contact inserted between the thermocouple and the safety valve by a predetermined relay operation. In a gas appliance, a failure detection circuit that detects a failure in the state where the relay contact cannot be turned off, and when the failure is detected by this failure detection circuit, a voltage of the opposite polarity to the thermoelectromotive force of the thermocouple is applied to the safety valve. And a reverse voltage applying circuit for closing the safety valve, and a safety valve control circuit for a gas appliance.