JPS6218810B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flame detection device comprising a flame rod, a rectifier circuit for smoothing flame current detected by the flame rod, and a reference potential to be compared with the potential of the rectifier circuit. The purpose of this invention is to provide a flame detection device equipped with a protection circuit that prevents parts from being destroyed and ignition detection malfunctions if the applied flame rod short-circuits with the counter electrode for some reason. be.

A conventional flame detection device will be described below with reference to the drawings. FIG. 1 shows a conventional example. In Figure 1, a rectifier circuit consisting of a frame rod 1', a resistor 2' and a capacitor 3', a reference potential consisting of a resistor 4' and a resistor 5', a resistor 6', a resistor 7', and a resistor 8 are shown. ', comparator 9', and capacitor 1
0' and the transformer 11' constitute a flame detection device.

Next, the operation of the configuration shown in FIG. 1 will be explained. That is, a parallel circuit of a resistor 2' and a capacitor 3' is connected to the transformer 11' via a resistor 8'.
The other connection point of the parallel circuit is connected to frame rod 1'. The other terminal of the transformer 11' is connected to the opposite electrode of the frame rod 1', and an alternating current voltage is applied between the frame rod 1' and the opposite electrode. When a combustion flame is detected by the flame rod 1', an ion current is detected;
The flame detection voltage can be taken out by a parallel circuit consisting of a resistor 2' and a capacitor 3'. A comparator 9 compares the flame detection voltage detected as the output of the parallel circuit with the potential at the connection point between the resistors 4' and 5', which is a reference potential obtained by dividing the DC power supply voltage by the resistors 4' and 5'. ′ to determine whether the combustion flame has reached the green combustion state.

If the flame rod 1' is short-circuited to the opposite electrode for some reason, the AC voltage generated from the transformer 11' will be applied to the combustion flame from the flame rod 1' via the resistor 8' and the resistor 2' until now as an AC electric field. However, when the flame rod 1' is short-circuited to the burner head, which is the counter electrode, the AC voltage is divided by the ratio of the composite impedance seen from both ends of the resistor 8' and the detecting circuit from both ends of the resistor 2'. Ru. Therefore, when the potential detected across the capacitor 3' reaches the ignition detection level, an erroneous operation occurs in which ignition detection is determined even though no combustion flame is generated. Furthermore, if the capacitor 3' is a polar capacitor, if an AC voltage higher than the reverse withstand voltage is applied, internal deterioration or destruction may occur, which is extremely dangerous.

Therefore, the present invention eliminates these conventional drawbacks, and one embodiment thereof will be described below with reference to FIG. 2.

In FIG. 2, a frame rod 1, a resistor 2, and a capacitor 3 constitute a rectifier circuit.
A reference potential circuit is constructed by dividing the DC power supply voltage between resistor 4, resistor 4'', and resistor 5.In the reference potential circuit, the potential at the connection point between resistor 4'' and resistor 5 sets the ignition detection level, and the reference potential circuit is , and the potential at the connection point between resistor 4 and resistor 4'' is higher than the first dividing point potential. 6 is a resistor, 7 is a resistor, 8 is a resistor, 9 is a comparator, 10 is a capacitor, 11 is a transformer, and 12 is a Zener diode.The cathode side of the Zener diode 12, which is a constant voltage element, is connected to the dividing point between the resistor 4 and the resistor 4'', and the anode side of the Zener diode 12 is connected to the dividing point between the resistor 4 and the resistor 4''. ,
It is connected to the negative side of a resistor 2 and a capacitor 3 forming a rectifier circuit, and is connected to a resistor 6. Furthermore, the other terminal of the resistor 6 is connected to the − of the comparator 9.
connected to the terminal.

The Zener diode 12, which is a constant voltage element, has the role of regulating the potential charged to the rectifier circuit (resistor 2 and capacitor 3) when ignition is detected normally, and a voltage higher than the power supply voltage is applied to the − input terminal of the comparator 9. and prevents it from being destroyed. This is impossible with regular diodes because they do not provide constant voltage characteristics. A protection circuit for preventing ignition detection malfunction is constructed by a resistor 8 as a current limiting means, a capacitor 3 forming a part of a rectifier circuit, and a constant voltage means of a Zener diode 12 to prevent ignition detection malfunction.

Next, the operation of this configuration will be explained.

Now, let us consider a case where the flame rod 1 is short-circuited with the burner head, which is the opposing electrode, for some reason.
The path through which the alternating current generated in the transformer 11 flows is first considered to be the path of the transformer 11 -> the resistor 8 -> the capacitor 3 -> the frame rod 1 -> the counter electrode -> the transformer 11. Next, another path is created: transformer 11 -> counter electrode -> flame rod 1 -> Zener diode 12 -> resistor 4 -> resistor 8 -> transformer 11. In the case of the former path, by setting the capacitance value of the capacitor 3 to be somewhat large, the potential across the capacitor 3 becomes lower than the ignition detection level, so there is no problem. In the latter path, that is, the path through which the signal of the remaining half cycle of the AC signal passes, it is sufficient that the sum of the forward voltage drop across the Zener diode 12 and the voltage drop across the resistor 4 is below the ignition detection level. The reference potential divides the DC power supply voltage by the ratio of the resistance value of the sum of the resistors 4 and 4' to the resistor 5, and the Zener diode 12 is connected to the connection point of the resistors 4 and 4'. Therefore, since the resistor 4 can take a relatively small value, and the forward voltage drop of the Zener diode 12 is small, the sum of the forward voltage of the Zener diode 12 and the voltage drop of the resistor 4 is sufficient. lower than the ignition detection level, and
The reverse withstand voltage of capacitor 3 is lower than that. Therefore, no ignition detection malfunction occurs, and no reverse withstand voltage is applied to the capacitor 3, so there is no risk of it being destroyed.

As described above, according to the flame detection device of the present invention, when the flame rod 1 causes a short circuit accident to the opposite electrode for some reason, the current limiting means (for example, the resistor 8) and the constant voltage means (for example, the Zener diode 12) ) to form a protection circuit by forming a path for passing the alternating current signal generated by the transformer,
Safety is dramatically increased against ignition detection malfunctions and parts destruction, and great effects can be obtained with a simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional flame detection device, and FIG. 2 is a circuit diagram of a flame detection device according to an embodiment of the present invention. 1...Frame rod, 2...Resistor, 3...Capacitor (resistance 2 and capacitor 3 constitute a rectifier circuit) 4, 4', 5...Resistor (determining the reference potential), 8... ...Resistance (current limiting element), 9
... Comparator, 12 ... Zener diode (resistance 8
The capacitor 3 and the Zener diode 12 constitute a protection circuit for preventing ignition detection malfunction. ).

Claims (1)

[Claims] 1. A flame rod that detects a combustion flame, a rectifier circuit that smoothes the flame current obtained from this flame rod, a reference potential circuit that outputs a reference potential to be compared with the potential of this rectifier circuit, and the potential of the rectifier circuit and the reference potential. a comparator for determining whether or not the combustion flame has reached a green combustion state by comparing the flame rods; a current limiting means for limiting a short circuit current generated when the flame rod causes a short circuit accident; Connected in parallel with the rectifier circuit from a second division point that is higher in potential than the first division point at which the ignition detection determination level is set, and connected so that the potential becomes equal to or lower than the ignition detection level of the reference potential circuit when the flame rod is short-circuited. and a constant voltage means.