JPS5875663A - Thermostat circuit for hot water temperature in water heater - Google Patents

Abstract

PURPOSE:To prevent water from being boiled due to opeated ooerations at the time of a disconnection and prevent an erroneous operation of a disconnection-detecting circuit from occuring at the time of an extreme fall of temperature, by a method werein a detection level of a disconnection-detecting operation is changed for a predetermined period of time after the start of combustion in a water heater so that the disconnection can be detected even in the predetermined period of time. CONSTITUTION:When the hot water temperature is low, a comparator 12 generates an output ''1'', whereby a burner motor driving circuit 15 is turned ON, charging of a capacitor 17 is simultaneously started, a combustion-controlling ciruit 19 is turned ON, and combustion is started. In addition, charging of a capacitor 21 is started, at which moment a transistor 10 is in an OFF condition. Accordingly, the disconnection-detecting circuit 13 is not operated unless the resistance value of a thermistor 2 becomes extremely high, so that a normal operation is retained even when the temperature is lowered to 0 deg.C. When charging of the capacitor 21 proceeds to reach a voltage higher than a threshold valvue of a circuit 23, a transistor 10 is turned ON, and the detection level is changed to a normal set level. When a disconnection occurs in a thermistor 2, the output of the camparator 13 becomes ''1'' because the potential at a point (a) is 0V, so that a signal is fed to a safety circuit 24, a contact 25 is opened, and the combustion operation is stopped.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hot water temperature thermo circuit V of a hot water boiler. - Even if the resistance value of the mister becomes extremely large, the disconnection detection circuit does not activate and continues to operate normally.

Generally used for temperature detection; for those that use a thermistor, the relationship between the temperature-resistance characteristics of the thermistor and the operational stability (detection, precision change) of the electronic circuit is approximately 0"C to 100"C.
It is usual to have temperature detection in the range of . There is a problem with the hot water boiler for hot water supply that it freezes when the temperature drops below 10°C, so from that point of view it was a good idea to detect 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''C, the resistance of the thermistor becomes too large, resulting in the same result as if the thermistor were disconnected, causing the disconnection detection function to become inoperable.

For this reason, various methods have been used in the past in which the disconnection detection circuit is turned off for a predetermined period of time at the start of operation, and the disconnection detection circuit is activated after the temperature of the hot water rises due to combustion. However, in this case, the wire breakage detection circuit is activated for a predetermined period of time each time the operation is started, so if the wire is actually broken, and repeated operation is performed for a short period of time, there is a problem that the boiling state continues. Ta.

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 explained below based on the electric circuit shown in the figure. -1 is a power supply for the control circuit, 2 is a thermistor for water temperature detection, 3 to 9 are resistors, and 4 is for changing each detection level for a predetermined time. It is a resistance for 10 is a transistor; 11 to 13 are comparators; 11 is for detecting excessive temperature change; -12 is for hot water temperature control;
3 is for disconnection detection. 14 is a diode, 16 is a burner motor 1.1J); moving instep circuit, 16 is a resistor, 17 is a capacitor, 18 is an AND circuit, and these 16 to 18 glI
This product constitutes the bleep-purge timer circuit. 19 is a combustion overturning circuit, 20 is a resistor, 21 is a capacitor, 22it
Diode, 23 is an AND circuit, these parts 20 to 23 are used to change the detection level at the beginning of combustion and form a timer circuit T, 24 is a safety circuit, and 26 is a contact point.
2. A signal from the safety circuit 24 causes the contact to be connected.

To explain the operation of the control circuit having the structure described above, first, when the hot water temperature is low, the resistance value of the hot water temperature thermistor 2 is large, so Va<Vc, and the comparator 12 outputs 1.
Thus, the burner motor drive circuit 15 is turned on.

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 the output 1) - and the combustion control (b) path 1
Turn on 9 and start combustion. Further, the output 1 of the AND circuit 18 starts charging the capacitor 21 via the resistor 20. At this point, the output of the 14 A N D circuit 23 is ○, so the transistor 101d is in the FF state.

That is, since the lightning level at point a is determined by the hot water temperature thermistor 2 and the resistor 3.4, 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 hot water temperature detection becomes extremely low, the disconnection detection circuit 13
does not operate, and even if the temperature drops below O''CC, it will not detect a disconnection and will operate normally.At this point, the capacitor 21 is charged and exceeds the threshold of the AND circuit 23. The AND circuit 23 becomes output 1, turns on the transistor 1o, shorts the resistor 4, and changes it to the normal setting level.From then on, the diode 22VC forms self-holding, so detection is performed at the normal setting level. It is.

Next, when the hot water temperature thermistor 2 is disconnected (l), the potential at point a is ○V regardless of whether the transistor 1o is on or off, so Va (Vd), and the comparator 13 The output becomes 1, which supplies a signal to the safety circuit 24, opens the contact 25, and stops the combustion operation.

As described above, according to the present invention, after the start of combustion, the set value of the wire breakage detection level is changed and increased by 11 for a predetermined period IIy, so that wire breakage can be detected regardless of the time interval. It is possible to prevent boiling due to repeated operation, and also to prevent malfunction of the disconnection detection circuit when the temperature change is extremely low.

[Brief explanation of the drawing]

The figure is a circuit diagram showing one embodiment of the present invention. 2-・・・Hot water temperature test, button thermistor, 3.4...
...Resistance, T...-Timer circuit.

Claims (1)

[Claims] 1 hot water temperature thermo circuit of the hot water boiler connected to the output end of the 1 timer circuit that operates in the early stage of combustion.