JPH1194246A - Ignition sensor circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a necessity of adding another step for performing adjustment for every amplifier even if the amplifier such as an operation amplifier of low price is applied in an ignition sensor circuit. SOLUTION: Influence of either an offset or a biasing power supply Eb is cancelled by a method wherein a difference between an output of an operation amplifier 2 when a thermoelectromotive force under a turned-on of a switch element S3 is not inputted to the operation amplifier 2 and another output of the operation amplifier 2 when the thermoelectromotive force is inputted under a turned-on state of any one of the switch elements S1, S2 is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ignition detection device for detecting an ignition state of a burner of a gas appliance, for example.

[0002]

2. Description of the Related Art In a conventional device of this type, since the voltage of a thermoelectromotive force output from a thermocouple is about several mV, it is amplified by an operational amplifier which is an amplifier, and the amplified voltage is converted into a digital signal. When the output voltage of the operational amplifier becomes higher than a predetermined voltage value, it is determined that the ignition state is established.

[0003]

SUMMARY OF THE INVENTION In the above prior art,
Since the voltage of the thermoelectromotive force is extremely low, the offset voltage is low when an operational amplifier is used for voltage amplification (low offset).
It is necessary to use a high precision operational amplifier. However,
Since the low offset operational amplifier is expensive, there is a problem that the ignition detection device becomes expensive. On the other hand, it is possible to use a relatively low-cost operational amplifier,
In this case, since the offset voltage is high and the offset voltage varies for each operational amplifier, it is necessary to provide an adjustment step for canceling the offset. Therefore, there is a problem that the cost of the ignition detection device is increased.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide an ignition detection device which does not require additional steps such as adjustment for each operational amplifier even if a low-cost operational amplifier is used. .

[0005]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention amplifies a thermoelectromotive force generated by a thermocouple disposed at a position heated by a burner or another heat source by an amplifier, and the amplifier amplifies the thermoelectromotive force. In an ignition detection device that detects that a heat source is in an ignition state when an amplified voltage is higher than a predetermined value, switching is performed between a state in which thermoelectromotive force is input to an amplifier and a state in which thermoelectromotive force is not input to the amplifier. Means for detecting an ignition state by comparing a voltage difference between an output voltage of the amplifier in a state where the thermoelectromotive force is input and an output voltage of the amplifier in a state where the thermoelectromotive force is not input with the predetermined value. And a voltage for performing the operation.

The output of the amplifier includes a thermoelectromotive force component and an offset voltage component. On the other hand, the output of the amplifier in a state where the thermoelectromotive force is not input includes the offset voltage component of the offset voltage but does not include the thermoelectromotive force component. Therefore, when the difference between the output of the amplifier when the thermoelectromotive force is input and the output of the amplifier when the thermoelectromotive force is not input is obtained, the offset voltage component is canceled and the The components can be removed.

In particular, when the ignition state is detected by a microcomputer by converting the output voltage of the amplifier into a digital signal, if the power supply is a single power supply, the amplifier that generates the offset voltage on the negative side will have a converter that converts the digital signal to 0 V or less. Is input and cannot be converted, a bias voltage is required, but the effect of the bias voltage can be canceled together with the effect of the offset voltage.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, reference numeral 1 denotes a microcomputer for controlling the operation of gas appliances such as a gas table provided with two gas burners (not shown) and a gas water heater.
Note that electromagnetic safety valves SV1 and SV2 are interposed in a gas supply pipe (not shown) for supplying gas to the gas burner.
Then, the microcomputer 1 controls the transistors TR1 and TR2 connected in series to open and close the electromagnetic safety valves SV1 and SV2.

The microcomputer 1 has a built-in A / D converter for converting an analog signal into a digital signal, and an A / D converter for inputting the analog signal to the A / D converter.
The output terminal of the operational amplifier 2 as an amplifier is connected to the D terminal. The switching elements S1 and S2 are connected in series to the minus terminals of the two thermocouples TC1 and TC2 arranged at positions heated by the respective burners. Then, the other of the switch elements S1 and S2 was connected to each other and connected to the minus terminal of the operational amplifier 2 via the resistor R1.
On the other hand, a resistor R1 and a resistor R
2, a resistor R3 (= R1 // R2) and a bias power supply Eb are connected in series. The two thermocouples TC1 and T1 are connected between the switch elements S1 and S2 and the resistor R1.
A switch element S3 for preventing the thermal electromotive force of C2 from being input to the operational amplifier 2 and for switching only the voltage of the bias power supply Eb to the operational amplifier 2 was attached. Each of the switch elements S1, S2, S3 is normally off, but the signals T1, T2,
It is turned on by T3. Reference numeral 3 denotes a power supply for the microcomputer 1, which supplies power to the microcomputer 1 via a regulator 31 that stabilizes the voltage at Vref.

When signals T1, T2, and T3 are output from the microcomputer 1 at the timing shown in FIG.
S2 and S3 are ON / OFF controlled so that only one of them is always in the ON state. When the switch element S1 is turned on, the thermoelectromotive force output from the thermocouple TC1 is input to the operational amplifier 2, and when the switch element S2 is turned on, the thermoelectromotive force output from the thermocouple TC2 is output from the operational amplifier 2.
Is input to When the switch element S3 is turned on, the operational amplifier 2 does not receive the thermoelectromotive force of any of the thermocouples TC1 and TC2.
Only the voltage Vb of b is input.

Here, the external gain of the operational amplifier 2 is represented by R2 /
R1 and one of the switch elements S1 and S2 are turned on, the voltage of the thermoelectromotive force input to the operational amplifier 2 is Vtc, the output voltage of the operational amplifier 2 at that time is Von,
When the switch element S3 is on, the output voltage of the operational amplifier 2 is Voff, and the offset voltage of the operational amplifier 2 is Vos.
Then, Von and Voff can be expressed as follows: Von = (Vb−Vtc + Vos) × (R2 / R1) Voff = (Vb + Vos) × (R2 / R1)

The difference between Von and Voff is Von−Voff = −Vtc × (R2 / R1), and Vtc = − (Von−Voff) × (R1 / R2) is obtained.

As is apparent from the equation, Vtc is not affected by Vb and Vos.

As described above, the Vt calculated inside the microcomputer 1 is
When c is higher than a predetermined threshold value, the microcomputer 1 determines that the gas burner has ignited and holds the electromagnetic safety valve open. When it is lower than the threshold value, it determines that the ignition has failed or determines that a misfire has occurred. Then, the electromagnetic safety valve is closed to prevent the unburned gas from being released from the gas burner.

Since it is not affected by at least Vos,
Even if an inexpensive operational amplifier is used without using an expensive operational amplifier with a low offset, the influence of the offset voltage can be eliminated without adjusting the operational amplifier individually.

The switching elements S1, S2, S3 use FETs (field effect transistors), relays and the like.

[0017]

As is apparent from the above description, according to the present invention, even if an amplifier such as an inexpensive operational amplifier is used for the ignition detection device, it is necessary to add a separate process for adjusting each amplifier. Absent.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing timing for controlling opening and closing of a switch element;

[Explanation of symbols]

 1 microcomputer 2 operational amplifier (amplifier) 3 power supply TC1 thermocouple TC2 thermocouple

Claims (1)

[Claims] An amplifier amplifies a thermoelectromotive force generated by a thermocouple disposed at a position heated by a burner or another heat source, and when the voltage amplified by the amplifier is higher than a predetermined value, the heat source is ignited. A switching means for switching between a state in which the thermoelectromotive force is input to the amplifier and a state in which the thermoelectromotive force is not input, and an amplifier in a state in which the thermoelectromotive force is input. An ignition detection device characterized in that a voltage difference between the output voltage of the amplifier and the output voltage of the amplifier in a state where the thermoelectromotive force is not input is compared with the predetermined value to detect an ignition state.