JPS6131790B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hot water temperature thermocircuit for a hot water boiler, in which the set value of a disconnection detection circuit is increased for a predetermined period of time at the beginning of combustion, and the resistance value of the thermistor for hot water temperature detection is increased at low temperatures. Even if the wire becomes extremely large, the disconnection detection circuit will not activate and will continue to operate normally.

Generally, when a thermistor is used to detect hot water temperature, the temperature can be detected in the range of approximately 0°C to 100°C due to the relationship between the temperature-resistance characteristics of the thermistor and the operational stability (detection and accuracy) of the electronic circuit. is always the case. In addition, hot water boilers for hot water supply have the problem of freezing when the temperature drops below 0°C, and from this point of view, there is no need to consider detecting temperatures below 0°C. However, in hot water boilers for heating, antifreeze is used as a heat medium, so there is no problem of freezing and the boiler must operate normally at any temperature. However, when the outside air drops below 0℃, the resistance of the thermistor becomes too large, resulting in the same result as if the thermistor were disconnected.
There was a problem where the disconnection detection function was activated and stopped working. Conventionally, therefore, a method has been adopted in which the disconnection detection output is turned off for a predetermined period of time at the start of operation, and the disconnection detection circuit is activated after the hot water temperature rises due to combustion. However, in this case, since the wire breakage detection circuit does not operate for a predetermined period of time each time the operation is started, there was a problem in that even if the wire was actually broken, the boiling state continued if the operation was repeated for a short period of time.

The present invention has been made to solve these problems, and is designed to change the detection level for wire breakage detection during a predetermined period of time at the beginning of operation.

An embodiment of the present invention will be described below based on the electric circuit shown in the figure. 1 is a power supply for the control circuit, 2 is a thermistor for detecting hot water temperature, 3 to 9 are resistors, 3 is a resistor for temperature setting, and 4 is a resistor. This is a resistor for changing each detection level for a predetermined period of time. 10 is a transistor, 11-1
3 is a comparator, 11 is for detecting excessive temperature rise, 12 is for hot water temperature control, and 13 is for detecting disconnection. 14 is a diode, 15 is a burner motor drive circuit, 16 is a resistor, 17 is a capacitor, and 18 is an AND circuit, and these components 16 to 18 constitute a prepurge timer circuit. 19 is a combustion control circuit, 20 is a resistor,
21 is a capacitor, 22 is a diode, 23 is a
In the AND circuit, these parts 20 to 23 form a timer part T to change the detection level at the early stage of combustion. 24 is a safety circuit, and 25 is a contact, which is opened by the signal from the safety circuit 24. .

To explain the operation of the control circuit having the above configuration, first, when the water temperature is low, the resistance value of the water temperature thermistor 2 is large, so Va<Vc,
The comparator 12 has an output of 1, turning on the burner motor drive circuit 15. At the same time, charging of the capacitor 17 is started via the resistor 16, and when the charging progresses to the threshold value of the AND circuit 18, the AND circuit 18 becomes an output 1, turns on the combustion control circuit 19, and starts combustion. Furthermore, the output 1 of the AND circuit 18 starts charging the capacitor 21 via the resistor 20. At this point, the output of the AND circuit 23 is 0, so the transistor 10 is in an OFF state. That is, since the potential at point a is determined by the hot water temperature thermistor 2 and the resistors 3 and 4, the set values of each detection circuit have increased. In other words, in the disconnection detection circuit,
Unless the resistance value of the thermistor 2 for detecting hot water temperature becomes extremely large, the disconnection detection circuit 13 will not operate, and even if the temperature drops below 0°C,
It does not detect disconnection and operates normally. Here, charging of the capacitor 21 progresses and when the threshold value of the AND circuit 23 is exceeded, the AND circuit 23 becomes output 1,
Turn on transistor 10, short-circuit resistor 4,
Change to the normal setting level. Thereafter, since the diode 22 forms self-holding, detection is performed at the normal setting level.

Next, we will discuss the case where the hot water temperature thermistor 2 is disconnected. When the hot water temperature thermistor 2 is disconnected, the potential at point a is OV regardless of whether the transistor 10 is on or off, so Va<
Vd, the output of the comparator 13 becomes 1, and a signal is supplied to the safety circuit 24, which opens the contact 25 and stops the combustion operation.

As described above, according to the present invention, since the set value of the wire breakage detection level is changed for a predetermined period of time after the start of combustion, a wire breakage can be detected regardless of the time period, and boiling In addition, it is possible to prevent the disconnection detection circuit from malfunctioning when the temperature drops extremely.

[Brief explanation of the drawing]

The figure is a circuit diagram showing one embodiment of the present invention. 2...Thermistor for water temperature detection, 3, 4...Resistor, T...Timer circuit.

Claims (1)

[Claims] 1. Connect a temperature setting resistor and a detection level variable resistor in series with the hot water temperature sensing thermistor, and compare the output with a reference potential between the hot water temperature sensing thermistor and the temperature setting resistor. A hot water temperature thermostat for a hot water boiler in which a comparator for controlling the hot water temperature is connected, the output end of this comparator is connected to a timer section together with the combustion control circuit, and the output end of this timer section is connected to the connection point of both of the resistors. circuit.