JPH0435714Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a flame detection circuit used in combustion appliances.

BACKGROUND TECHNIQUE Conventionally, a structure for detecting the presence or absence of a combustion flame has generally utilized the electrical rectification effect of the flame formed in a burner, and a specific example thereof is as shown in FIG. A flame rod 1 is provided in the flame F that is formed, and a voltage from an AC power source S is applied between it and the burner 2. When there is a flame F, this AC signal is rectified and then passed through a low-pass filter 3 to a DC voltage. is generated and inputted to one input terminal 4a of the voltage comparator 4. On the other hand, a reference voltage for voltage comparison is input to the other input terminal 4b of the voltage comparator 4 as a DC reference voltage obtained by dividing the DC power supply 5 by resistors 6 and 7. Furthermore, a Zener diode 8 for protecting the voltage comparator 4 is provided on the output side of the low-pass filter 3. That is, in general, the voltage comparator 4 has the possibility of being destroyed or malfunctioning at an input voltage higher than the voltage of the DC power supply 5 which is its driving power supply, and in the circuit example shown in FIG. 2, the resistance within the flame F is small. The Zener diode 8 is provided to prevent one input terminal 4a of the voltage comparator 4 from exceeding the voltage of the DC power supply 5 at times.

Problems to be Solved by the Invention Therefore, when designing a flame detection circuit, the value of the rectified current flowing through the flame F multiplied by the resistance value of the resistor 9 in the low-pass filter 3 should be used as the voltage of the flame detection DC. , this value is forced to be higher than the reference voltage for detection at the other input terminal 4b of the voltage comparator 4 when the presence of the flame F is detected. However, the value of the rectified current flowing through the flame F is only about several microamperes, and if the design is based on this, the reverse current of the Zener diode 8 for protecting the voltage comparator 4 cannot be ignored. (This is because the reverse current of the Zener diode 8 may reach several microamperes below the breakdown voltage.) Furthermore, the reverse current of the Zener diode 8 has a large error and may also have poor temperature dependence. However, accurate design was difficult.

Means for Solving the Problems The present invention has been made to solve the above problems, and is a voltage comparator that is higher than the detection reference voltage applied to the other input terminal of the voltage comparator and A potential point having a voltage lower than the voltage input to one input end of the voltage comparator is provided, one input end of the voltage comparator is an anode, and a diode is provided with the potential point connected to a cathode.

As a result, the diode does not operate until one input end of the voltage comparator becomes higher than the potential point voltage, so at the battery level, the flame detection direct current is calculated by multiplying the rectified current value of the flame by the value of the resistance. Accurately capture it as voltage.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1 showing the flame detection circuit of the embodiment, S
is an AC power supply, and a flame rod 1 and a burner 2 are connected in series to this AC power supply S via a flame F, and a low-pass filter 3 consisting of a parallel circuit of a plurality of capacitors and a resistor 9 is connected between the flame rod 1 and the AC power supply S. It is connected. A voltage comparator 4 has one input terminal 4a connected to the connection point between the resistor 9 and the anode of the diode 13, and the other input terminal 4b connected to the connection point between the resistors 11 and 12. 10 is also a resistor, and both resistors 1
1 and 12 are connected in series to the DC power supply 5, and the cathode of the diode 13 is connected to a potential point A formed by the connection point of the resistors 10 and 11. At this time,
Potential at potential point A > other input terminal 4 of voltage comparator 4
The input voltage to b is...

Next, the operation of this embodiment will be explained.

When the voltage at the output side of the low-pass filter 3 is lower than the voltage at potential point A, the diode 13 is off and the reverse current is very small, so the voltage at one input terminal 4a of the voltage comparator 4 is equal to that of a flame. The value obtained by multiplying the value of the rectified current flowing through F by the resistance value of the resistor 9 in the low-pass filter 3 can be taken as an accurate value, and this voltage and the other input terminal of the voltage comparator 4, which is the reference voltage for detection, can be taken as an accurate value. The presence or absence of the flame F is accurately detected based on the magnitude relationship of the voltage of 4b. In addition, when the voltage on the output side of the low-pass filter 3 is higher than the voltage at potential point A, the diode 13 is turned on,
The voltage at one input terminal 4a of the voltage comparator 4 is equal to the flame F.
Since it is lower than the value obtained by multiplying the rectified current flowing through the filter by the resistance value of the resistor 9 in the low-pass filter 3,
The operation based on the output relationship of voltage comparator 4 is always flame F.
The flame is normally detected so that it is determined that there is a flame.

Effects of the invention As described above, according to the invention, the flame detection level can be accurately determined as the flame detection DC voltage multiplied by the rectified flame current value and the resistance value, and the design can be improved. A reliable and easy flame detection circuit can be obtained.

[Brief explanation of the drawing]

FIG. 1 shows a circuit diagram of a flame detection circuit according to an embodiment of the present invention, and FIG. 2 shows a conventional circuit diagram of the same. 1...flame rod, 2...burner, 4...
Voltage comparator, 4a...input end, 4b...input end,
13...Diode, A...Potential point, F...Flame, S...AC power supply.

Claims (1)

[Scope of utility model registration request] A flame rod 1 is provided in a flame F, and an AC power source S is provided between the burner 2 which forms the flame F and the flame rod 1. A flame detection DC voltage is applied to the input terminal 4a by electrical rectification between the flame rod 1 and the burner 2 via the flame F.
A voltage comparator 4 is provided for applying a reference voltage to the other input terminal 4b, and the presence or absence of the flame F is detected through the output state of the voltage comparator 4 which differs depending on the voltage applied to both input terminals 4a, 4b. A potential point A having a voltage higher than the voltage applied to the other input terminal 4b of the voltage comparator 4 and lower than the voltage applied to the input terminal 4a is connected to the voltage comparator 4.
a diode 13 having a cathode connected to the potential point A and an anode connected to the input terminal 4a.