JPS6324217B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a safety device when a thermistor for controlling a vaporization heater of a liquid fuel combustion apparatus is disconnected.

Generally, when the temperature of a vaporization heater is controlled using a temperature-dependent element such as a thermistor, the operating temperature is extremely wide from about -20℃ to 400℃, so the variation range of the thermistor is from several 10 MΩ to several 100 Ω. Become.
It is impossible for the control circuit to detect such an extremely wide range of resistance values, so after turning on the operation switch,
A timer circuit was provided to prevent the disconnection detection circuit from operating for a predetermined period of time. Next, if the disconnection detection circuit is activated, it is recommended to immediately stop all operations.If the reset is repeated, the temperature of the vaporizing section will rise abnormally, so if the disconnection detection circuit is activated, A method has been considered in which the vaporization heater is turned off, then only the burner motor is operated for a predetermined period of time to cool the vaporization section, and then all operations are stopped. Conventionally, the off-timer and burner motor forced-on timer of the disconnection detection circuit were constructed from separate timer circuits, which caused a problem in that they were very expensive.

The present invention was made in order to solve this problem, and the output of the differentiating circuit, which is operated by the output of the comparator that detects the disconnection of the thermistor that detects the temperature of the vaporization part of the burner, is connected to the reset terminal of the timer circuit. By connecting the timer circuit to
This time, operate it as a burner motor forced on timer. In this way, by using one timer circuit for two timer operations, the number of parts can be reduced and the cost can be reduced.

An embodiment of the present invention will be described below based on the drawings.
1 is a power supply for the control circuit, 2 is a thermistor for detecting the temperature of the liquid fuel vaporization part, 3 to 8 are resistors for setting each detection level, 9 to 11 are comparators, 9 is for detecting excessive temperature, 10 is a vaporization heater 11 is for detecting disconnection of the thermistor for detecting the temperature of the vaporization section; 12 is a vaporization heater drive circuit; the comparator 1 for controlling the vaporization heater;
13 is an OR circuit which is activated by the output of 0 and receives the outputs of comparators 9 and 11 as inputs and determines the output.
14 is a diode, 15 is a self-holding circuit for locking off the burner motor drive circuit 31 described later during preheating, 16 to 18 are drive circuits operated by the output of the OR circuit 13, 19 is a logic circuit,
20 is a capacitor, 21 is a resistor, 22 is a transistor, and these components 20 to 22 constitute a differential circuit, 23
is a resistor, 24 is a capacitor, 25 is an AND circuit,
26 is a timer circuit, 27 is a transistor, 28
is a resistor, 29 is a capacitor, 30 is a safety circuit, 3
1 is a burner motor drive circuit, 32 is a combustion control circuit, and 33 is a normally closed contact operated by the safety circuit 30.

In the control circuit having the above configuration,
To explain its operation, we will first discuss the case where the temperature of the vaporization part of the liquid fuel combustion device starts from below the disconnection detection level under normal conditions. Since the temperature of the vaporization part is low, the input relationship of each comparator is Va<Vd<Vc<Vb.
Therefore, the output of comparator 9 is 0, and the output of comparators 10 and 11 is 1. This turns on the heater drive circuit 12 and starts energizing the heater, and at the same time the self-holding circuit 15
is activated and sends an off signal to the burner motor drive circuit 31 to stop combustion. Further, since the output f of the timer circuit 26 is 1, the 1 signal from the comparator 11 turns on the transistor 27 and locks it to 0, thereby setting the output of the OR circuit 13 to the 0 state and preventing the safety circuit 30 from operating. When the temperature of the vaporizer rises due to the energization of the heater and Va>Vd, the output of the comparator 11 becomes 0, the timer circuit 26 times up, the output f becomes 0, and even though the transistor 27 is turned off, the output of the OR circuit 13 remains unchanged. The output remains 0, and the safety circuit 30 does not operate and continues to operate normally. When the temperature further increases and Va>Vc, the comparator 10 becomes 0 and the heater drive circuit 12 is turned off. As a result, the energization to the vaporization heater is stopped, and at the same time, a 0 signal is supplied to the self-holding circuit 15, and the off signal to the burner motor drive circuit 30 is released. The self-holding circuit 15 is configured to hold 0 once a 0 signal is input. At this point, the burner motor drive circuit 31 operates, driving the burner motor, and at the same time supplies a signal to the combustion control circuit 32 to perform the combustion operation.

Next, we will discuss the case where the thermistor 2 for detecting the temperature of the vaporizer is disconnected.
is Ov, and no matter how much the vaporizer temperature rises, Va
The relationship <Vd<Vc<Vb continues, that is, the heater continues to be energized as explained above. However, since the output of the comparator 11 also remains at 1, when the timer circuit 26 times out and the output f becomes 0 and the transistor 27 turns off, the OR circuit 13 goes to the 1 state, and the driving circuits 16 to 18 is turned on, the heater drive circuit 12 is turned off, and the burner motor drive circuit 31 is turned on. At the same time, the OR circuit 19 is set to 1 state, and the resistor 21, capacitor 20,
The differential circuit made up of the transistor 22 is activated. That is, the transistor 22 is turned on instantaneously with a time constant determined by the capacitor 20 and the resistor 21, and the reset terminal e of the timer circuit 26 is instantaneously set to 0, thereby resetting it. As a result, the timer circuit 26 counts again and continues the above sequence, that is, only the burner motor remains on for a predetermined period of time. After a predetermined period of time has elapsed, the AND circuit 25 enters the 1 state and the safety circuit 3
0, the contact 33 is opened, and all operations are stopped.

As described above, according to the present invention, two timer operations can be performed by connecting the output of the differential circuit operated by the output of the comparator that detects disconnection of the thermistor that detects the temperature of the vaporization part of the burner to the reset terminal of the timer circuit. It can be configured with one timer circuit, reducing the number of parts and cost.

[Brief explanation of the drawing]

The figure is an electrical circuit diagram showing a safety circuit of a liquid fuel combustion device according to an embodiment of the present invention. 2...Thermistor for temperature detection, 26...Timer circuit, e...Reset terminal.

Claims (1)

[Claims] 1 Connect a resistor in series with the temperature detection thermistor installed in the vaporizer that vaporizes liquid fuel, use the connection point as one input, and use the reference level set below the normal ON/OFF control temperature as the other input. A disconnection detection circuit constituted by a comparator as an input, a timer circuit that operates for a predetermined period at the beginning of operation and initializes the timer operation by supplying a signal to the reset terminal, and the output of this timer circuit. and a circuit that turns on the burner motor drive circuit for a predetermined period of time according to the output of the timer circuit when the disconnection detection circuit is activated, and when the timer circuit times up, the burner motor drive circuit is turned on for a predetermined period of time. A safety circuit for a liquid fuel combustion device, in which the output of a differential circuit activated by the output of the detection circuit is connected to the reset terminal of the timer circuit, and the off-circuit and on-circuit are controlled by one timer circuit.