JP2001021419A - Temperature sensing circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sense a fault occurring in an amplifying means by providing a varying circuit in an input unit of the means, and judging the fault from a change of an output signal occurring when operated. SOLUTION: A thermoelectromotive force of a thermocouple 2 due to a flame of a gas burner B is amplified by an operational amplifier 3, an ignition of the burner B is sensed by a controller 1, and a safety valve SV on the way of a gas tube GP is opened and held. When the burner B is flame-failed, the flame failure is judged due to a decrease of the force of the thermocouple 2, and the valve SV is closed. If the thermocouple 2 is disconnected, an output signal of the amplifier 3 always monitored by the controller 1 becomes a not normal value, and the controller 1 judges the disconnection of the thermocouple 2. Here, a transistor 4 for short-circuiting a connecting resistor 31 of a terminal 3b of the amplifier 3 is provided, periodically closed by the controller 1 to short-circuit the resistor 31. Then, if the amplifier 3 is normal, its output signal is changed in a predetermined width, but if the amplifier 3 is faulted, its output signal is not changed in its predetermined width, and hence the amplifier is judged as a fault.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature detecting circuit used for detecting a flame of a gas appliance.

[0002]

2. Description of the Related Art For example, in a gas appliance provided with a gas burner, a thermocouple heated by the flame of the gas burner is disposed near the gas burner, and the thermocouple is heated by the flame while the gas burner is ignited. 2. Description of the Related Art A temperature detection circuit for determining that a gas burner has not misfired by detecting a high temperature is known. Since the output voltage of the thermocouple is extremely low, this type of temperature detection circuit amplifies the output voltage of the thermocouple using an amplifying means such as an operational amplifier. The signal amplified by the amplifying means is input to, for example, a microcomputer and converted into a temperature. By the way, since a thermocouple has a very simple structure in which only two kinds of metals are joined, the only abnormality that occurs in the thermocouple is disconnection. When the thermocouple breaks, the temperature converted by the microcomputer or the like becomes an unusual temperature, so that it is possible to detect that the break has occurred when the converted temperature deviates from a predetermined temperature range. .

[0003]

However, when an abnormality occurs in the amplifying means, for example, an output signal that keeps the converted temperature within the normal range regardless of the input signal from the thermocouple occurs. On the other hand, the microcomputer cannot detect that an abnormality has occurred in the amplifying means. For example, even if the flame is extinguished, the microcomputer may determine that the flame exists.

In view of the above problems, it is an object of the present invention to provide a temperature detection circuit capable of detecting an abnormality in an amplifying means when the abnormality occurs.

[0005]

According to the present invention, there is provided an amplifying means for amplifying an output of a thermocouple.
In a temperature detecting circuit for detecting a temperature based on an output signal of the amplifying means, a fluctuation circuit for fluctuating a signal input to the amplifying means by a predetermined amount is provided at an input portion of the amplifying means, and the operation of the fluctuation circuit is operated. Abnormality judging means for judging an abnormality of the amplifying means based on a change in the output signal of the amplifying means occurring when the amplifying means is provided.

If the variable circuit is operated while the amplifier circuit is operating normally, the output of the amplifying means changes in conjunction with the operation of the variable circuit. If the output of the amplifying means fluctuates in conjunction therewith, it can be determined that the amplifying means is functioning normally.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, reference numeral 1 denotes a control device comprising a microcomputer, which amplifies a thermoelectromotive force of a thermocouple 2 disposed near a flame hole of a gas burner B by an operational amplifier 3 and amplifies the thermoelectric power. Input to the control device 1. Further, a safety valve SV is interposed in the middle of the gas gap GP for supplying gas to the gas burner B, and an ignition operation is performed on the gas burner B and the thermocouple is heated by the flame of the gas burner B, so that the gas burner B is heated.
When the control device 1 detects that the ignition has been performed, the control device 1 holds the safety valve SV open. Further, for example, when the gas burner B misfires due to wind or the like while the gas burner B is ignited, the thermoelectromotive force of the thermocouple suddenly decreases, and the control device 1 determines that the gas burner B has misfired due to the decrease in the thermoelectromotive force. The SV is closed. The operational amplifier 3 has two terminals 3a
Amplifying means for amplifying and outputting the potential difference between 3b;
The control device 1 constantly monitors the output signal of the operational amplifier 3. Then, when the thermocouple 2 is disconnected, for example, the output signal of the operational amplifier 3 becomes an unusual value, so that the control device 1 determines that an abnormal state of disconnection of the thermocouple has occurred and reports the fact. By the way, it is conceivable that a value in the normal range is output to the control device 1 even if the operational amplifier 3 breaks down and the thermocouple 2 is disconnected, or that the same value as during ignition is output even if the gas burner B misfires. If such a failure occurs in the operational amplifier 3, the occurrence of an abnormality cannot be detected even if the control device 1 constantly monitors the output signal of the operational amplifier 3. Therefore, a transistor 4 for short-circuiting the ground resistor 31 of one terminal 3b of the operational amplifier 3 is provided so that the transistor 4 can be opened and closed by a signal from the control device 1. The control device 1 periodically closes the transistor 4 at a predetermined timing to short-circuit the ground resistor 31. As described above, since the operational amplifier 3 amplifies and outputs the potential difference between the terminals 3a and 3b, if the ground resistor 31 is short-circuited, if the operational amplifier 3 is functioning normally, the output signal has a fixed width. It fluctuates. On the other hand, if the operational amplifier 3 has failed, the output signal of the operational amplifier 3 does not fluctuate in the above-mentioned constant width even if the ground resistor 31 is short-circuited. Therefore, the control device 1 can determine whether or not the operational amplifier 3 is functioning normally based on the fluctuation range of the output signal of the operational amplifier 3 when the ground resistance 31 is searched. When it is determined that the operational amplifier 3 is out of order, the safety valve SV is closed and the fact is notified.

[0008]

As is clear from the above description, according to the present invention, it is possible to periodically check whether or not an abnormality has occurred in the amplifying means. It is possible to detect a failure that could not be detected conventionally, such as being fixed.

[Brief description of the drawings]

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Control device 2 Thermocouple 3 Operational amplifier 4 Transistor B Gas burner SV Safety valve

Claims (1)

[Claims] 1. A temperature detecting circuit comprising an amplifying means for amplifying an output of a thermocouple and detecting a temperature based on an output signal of the amplifying means, wherein a signal inputted to the amplifying means is inputted to an input part of the amplifying means. Is provided with a fluctuation circuit that fluctuates a predetermined amount,
A temperature detecting circuit, comprising: an abnormality judging means for judging an abnormality of the amplifying means from a change in an output signal of the amplifying means when the operation of the fluctuation circuit is operated.