JPS6247008Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a light leakage detection circuit in a combustion control circuit.

In a combustion control circuit, flame detection occurs when a flame detection element consisting of a photoconductor element, etc. that detects the presence or absence of a flame is exposed to light leaking from the outside world, or when the flame detection element malfunctions due to a short circuit. If an abnormal condition occurs in the circuit, the flame detection circuit will issue the same signal as if combustion was occurring, even though no combustion was actually occurring. As a result, since the combustion control circuit supplies fuel to the combustion chamber assuming that combustion is occurring, unburned fuel accumulates in the combustion chamber and may even leak out of the combustion chamber, creating a dangerous situation.

Conventionally, light leakage detection circuits for preventing such accidents have been constructed using a combination of transistors, diodes, etc., resulting in complex circuit configurations and signal processing, as well as low circuit reliability.

In order to eliminate the drawbacks of the conventional technology, the present invention
By inputting the signal output from the flame detection circuit and the signal output from the pre-purge circuit to a gate circuit in the form of an exclusive OR circuit, and performing exclusive OR and negation of the two inputs. The present invention provides a light leakage detection circuit with a simple configuration and high reliability. Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1a shows the configuration of an embodiment of the present invention,
FIG. 1b shows the input/output signal operation and truth table of FIG. 1a. 1 is a light leakage detection circuit composed of an exclusive NOR circuit 11, and when the input signals A and B are at the same level (both high level or both low level), the output signal The level is set to H, and when the signal levels of input signals A and B are of the opposite sex, the signal level of the output signal X is set to low level L. Input signal A is prepurge circuit 3
The signal level is set to be low level L while the prepurge is not completed, and to be high level H when the prepurge is completed. Input signal B is a signal output by the flame detection circuit 4, and when it is detected that there is a flame, such as when there is light leakage or when there is a flame after ignition, the input signal B goes to low level L.
If it is detected that there is no flame due to non-ignition, misfire, etc., it is set to a high level H. The signal X output from the light leakage detection circuit 1 controls the operation of the safety switch circuit 2, and when the signal level reaches a high level, the safety switch circuit 2 is operated.

In this embodiment configured in this way, the signal level of the signal
When the signal level of the output signal B of the flame detection circuit 4 and the output signal B of the flame detection circuit 4 are both low level L, that is, even though the pre-purge has not been completed, the flame detection circuit 4
When a false flame is detected as a flame even though there is no flame due to a malfunction such as light leakage or a short circuit in the flame detection element, and output signal A of the pre-purge circuit 3 and flame detection circuit 4. If the signal levels of the output signals B are both high level H, that is, even though the pre-purge has been completed, there is a failure in the combustion system and there is no ignition or misfire, so the flame detection circuit 4 detects that there is no flame. In either case, it is necessary to operate the safety switch circuit 2 to stop the function of the combustion system and issue an alarm. In addition, the prepurge circuit 3
When the output signal A of the flame detection circuit 4 and the output signal B of the flame detection circuit 4 have different signal levels, that is, when the pre-purge is incomplete and there is no flame, and when the pre-purge is completed and there is a flame. In both cases, the signal level of the signal X output from the light leakage detection circuit 1 becomes low level L, and the safety switch circuit 2
does not operate, and the operation of the combustion control circuit proceeds normally. As mentioned above, if there is light leakage in the flame detection circuit 4, the light leakage detection circuit 1 detects this light leakage while the pre-purge is not completed, activates the safety switch circuit 2 to issue an alarm, and detects the presence of light leakage. can be displayed.

FIG. 2 shows an embodiment of a combustion control circuit using the light leakage detection circuit shown in FIG. 1. The same reference numerals as in FIG.
1 is a DC power supply circuit that is driven by an AC power supply 7 and supplies DC; 6 is an AC drive unit;
an oil valve 62 that is actuated via the contact 351 of the relay 35 and supplies fuel to the combustion chamber, which operates when the pre-purge circuit 3 completes the pre-purge;
It includes an ignition transformer 63 for igniting fuel in the combustion chamber, a fan motor 64 for cooling, and an alarm 65 that is driven via contacts 251 of a relay 25 that is activated when the safety switch circuit 2 is activated. The safety switch circuit 2 receives the signal X output from the light leakage detection circuit 1.
When the signal level of the electrolytic capacitor 21 becomes high level H, the electrolytic capacitor 21 is charged through the resistor 22.
, an operational amplifier 23 that outputs a signal XR to a high level H when the charging voltage reaches a predetermined voltage value, and a relay 2 that operates via a transistor 24 when the signal XR reaches a high level H.
Consists of 5th grade. The prepurge circuit 3 includes an electrolytic capacitor 31 that is charged through a resistor 32 when DC is applied, an operational amplifier 33 that makes the output signal A high level H when the charging voltage reaches a predetermined voltage value, and a transistor. It is constituted by a relay 35 and the like which is activated by a signal A via a relay 34 and indicates that the pre-purge has been completed. The resistance value of the flame detection circuit 4 changes depending on the presence or absence of flame.
A flame detection element 41 made of CdS or the like, and when this flame detection element 41 receives flame light, its resistance value decreases, and its terminal voltage becomes below a predetermined value in relation to the resistor 42, an output signal B is generated. It is composed of an operational amplifier 43 and the like which sets the level of the signal to the low level L.

This embodiment configured as described above operates as follows. First, when the AC power supply 7 is energized, the ignition transformer 63 and fan motor 64 are started, and the DC power supply circuit 5 is operated via the control transformer 61, and the DC voltage is applied to the flame detection circuit 4, pre-purge circuit 3, and safety switch. are respectively applied to circuit 2. Here, we will discuss the case where the combustion control circuit is normal. Since the flame detection element 41 of the flame detection circuit 4 remains at a high resistance value since there is no flame, the operational amplifier 4
The level of the output signal B of No. 3 indicates a high level H,
On the other hand, the level of the output signal A of the operational amplifier 33 of the prepurge circuit 3 shows a low level L until the electrolytic capacitor 31 is charged through the resistor 32 and the prepurge is completed. Therefore, during this period, the input signal A of the light leakage detection circuit 1 is at the low level L, and the input signal B is at the high level H. Since the levels of both inputs are of the opposite sex, the output signal X is at the low level L. The normal operation can proceed without operating the safety switch circuit 2. Next, when the electrolytic capacitor 31 reaches a predetermined charging voltage value, the level of the output signal A of the operational amplifier 33 becomes high level H, the transistor 34 becomes conductive, operating the relay 35, closing the contact 351, and operating the oil valve 62. and start combustion. When combustion starts and a flame is emitted, the flame detection element 41 of the flame detection circuit 4 detects the flame and its resistance value decreases, and the output signal B of the operational amplifier 43 becomes low level L, and the input of the light leakage detection circuit 1 Since the signal A is at a high level H and the input signal B is at a low level L, the output signal X is at a low level L, and the safety switch circuit 2
Normal operation can proceed without activating.
Note that during this time, the prepurge is completed and the output signal A is
becomes a high level H, and the signal B remains at a low level H until combustion starts and flame is detected, and during this time, the input signals A and B of the light leakage detection circuit 1 both become a high level H. Therefore, the output signal X shows a high level H. However, the safety switch circuit 2 operates only when the electrolytic capacitor 21
This is when the charging voltage reaches a predetermined charging voltage value, and the safety switch circuit 2 will not malfunction due to this time delay.

Next, if there is light leakage to the flame detection circuit 4 or a failure such as a short circuit in the flame detection element 41, the flame detection circuit 4 outputs the signal B at the same time as the DC power is turned on. Set the signal level to low level L
On the other hand, the prepurge circuit 3 operates as in normal operation, and the signal A it outputs is at low level L while the prepurge is not completed, so the input signals A and B of the light leakage detection circuit 1 are both The signal X that it outputs becomes a high level H, operating the safety switch circuit 2, switching the contact 251 by operating the relay 25, stopping the driving of the oil valve 62, etc., and operating the alarm 65. to indicate that there is a malfunction such as light leakage. In addition, in the event of a failure such as when the pre-purge is completed but no ignition occurs, or when a misfire occurs during combustion, the output signal A of the pre-purge circuit 3 is already at a high level H, and the flame detection circuit 4 Since no flame is detected, the output signal of is also high level H, and since the input signals A and B to the light leakage detection circuit 1 are both high level H, the signal level of the output signal X is also high level H. , the safety switch circuit 2 is operated, the oil valve 62 is closed, and the alarm 65 is also operated to indicate that a failure has occurred.

In addition, in this embodiment, the prepurge circuit 3
The signal A outputted by the flame detection circuit 4 is at a low level L while the prepurge is not completed, and becomes a high level H when the prepurge is completed, and the signal B outputted by the flame detection circuit 4 is as follows.
When there is no flame, the level is set to high H, and when there is a flame, the level is set to low. The level may be set to be the opposite of that in the embodiment.

As explained above, according to the present invention, by using an exclusive OR circuit or a NOR circuit (generally referred to as an exclusive OR type circuit for convenience) and calculating the logical sum of each input signal, the It is possible to check for equipment failure or light leakage, and since each circuit operates independently, it has the effect of simplifying signal processing. Since a digital gate circuit is used, it is possible to obtain a light leakage detection circuit in a combustion control circuit that is inexpensive and highly reliable with a simple circuit configuration.

[Brief explanation of the drawing]

Figure 1a is a block diagram of an embodiment of the present invention;
FIG. 1B shows an operation table and a truth table of the input/output signals shown in FIG. 1...Light leakage detection circuit, 2...Safety switch circuit, 3...Pre-purge circuit, 4...Flame detection circuit,
5...DC power supply circuit, 6...AC drive section, 25,
35...Relay, 251,351...Relay 2
5, 35 contacts, 41...flame detection element, 62...
Oil valve, 62...Ignition transformer, 64...
Fan motor, 65...Alarm, A...Output signal of the pre-purge circuit, B...Output signal of the flame detection circuit, X...Output signal of the light leakage detection circuit, XR...Output signal of the safety switch circuit.

Claims (1)

[Scope of utility model claims] a prepurge circuit that generates a first level output signal when the prepurge is incomplete and a second level output signal when the prepurge is completed; and a first level output signal that generates the first level output signal when a flame is detected or due to a simulated flame. , a combustion control circuit having a flame detection circuit that generates an output signal of a second level when no flame is detected, a light leakage detection circuit, and a switch circuit, the light leakage detection circuit is connected to the output signal of the pre-purge circuit and the output of the flame detection circuit. The combustion control circuit is configured with a gate circuit that performs a logical operation of exclusive OR and its negation with a signal as input, and when the two input signals are input at the same level, the signal output from the gate circuit controls the combustion control circuit. A light leakage detection circuit for a combustion control circuit, characterized in that it detects an abnormal state and operates a safety switch circuit.