JPS59145423A - Control device of water heater - Google Patents

Abstract

PURPOSE:To prevent a dangerous over-combustion and provide a decreased number of component elements by a method wherein resistor elements for providing a reference voltage in a comparator for adjusting temperature and sensing excessive increasing of temperature are separately arranged. CONSTITUTION:When a thermistor 21 is troubled in its breaking line, a reversed input of a convertor 36 for detecting increased temperature and broken line is applied with a voltage having a partial voltage ratio between resistors 22 and 23. This voltage becomes higher than that applied when the thermistor 21 is not broken. When an output of a microcomputer 38 is at a high level, a reference voltage of the comparator 36 becomes high. However, this reference voltage is lower than a voltage applied to the reversed input of the comparator 36. Therefore, the output of the comparator 36 is at a low level and the microcomputer 38 senses the disconnection of the thermistor 21. An input port of the microcomputer 38 for use in inputting an output of the comparator 36 performs a discrimination of the input in synchronization with the output of said output port.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a control device for a water heater that heats water in a can by burning oil or the like.

The structure of the conventional example and its problems The conventional example will be explained based on the drawings. In Figure 1,
Reference numeral 1 denotes a thermistor for detecting the water temperature inside the can, to which a resistor 2 is connected in series, and a volume 3 for temperature adjustment is further connected in series. The voltage at the connection point between the thermistor 1 and the resistor 2 is proportional to the temperature of the thermistor 1, and the higher the temperature, the higher the voltage. 4 to 7 are resistors, all of which are connected in series.

The voltage given by the voltage division ratio of the resistor 4 and the resistors 6 to 7 is an over-rise detection signal that outputs an over-rise detection signal when the temperature of the thermistor 1 rises abnormally (that is, when it becomes an over-rise state). This is the reference voltage applied to the non-inverting input of a voltage comparator (hereinafter referred to as comparator 4) 8. The voltage given by the voltage division ratio of resistors 4 to 5 and resistors 6 to 7 is the voltage given by the thermistor 1.
This is the reference voltage applied to the non-inverting input of the temperature control comparator 9 which outputs a boiling signal when the temperature rises above the temperature control setting. The voltage given by the voltage division ratio of the resistors 4 to 6 and the resistor 7 is a reference voltage given to the non-inverting input of a disconnection detection comparator 10 that outputs a disconnection detection signal when the thermistor 1 is disconnected.

The resistor 11 is a feedback resistor that provides a differential when detecting excessive temperature rise, and the resistor 12 is a feedback resistor that provides a differential for setting the boiling temperature. 13 is a combustion operation based on the output signals of comparators 8 to 10;

This is a control circuit that performs stopping.

As explained above, the reference voltages to the comparators 8 to 100, each having a different function, are applied from the same resistance sides 4 to 7. Therefore, if a disconnection abnormality occurs in one of the resistors 4 to 7, there is a possibility that a plurality of functions will malfunction at the same time. For example, if the resistor 6 is disconnected, the reference voltage applied to the non-inverting inputs of the over-rise detection comparator 8 and the temperature control comparator 9 rises to the power supply voltage.

For this reason, even if the temperature of the thermistor 1 rises, temperature control and excessive rise detection do not operate, which poses a problem in that there is a risk of runaway combustion.

Therefore, in order to deal with this problem, comparators 8 to
Inserting a parallel resistor to the resistor that provides the reference voltage of 10,
A method such as providing a mechanical high limit is also considered, but this method has another problem of increasing the number of parts.

Purpose of the Invention In view of the above-mentioned problems, the present invention prevents the risk of runaway combustion by separating the resistance sides that provide reference voltages for the temperature control and overheat detection comparators, and also prevents overheat detection and overheat detection. It is an object of the present invention to provide a control device for a water heater with a reduced number of parts by detecting a disconnection using one comparator.

Structure of the Invention The basic structure of the present invention to achieve the above object includes a thermistor that detects the temperature of water inside the can of a water heater, and the voltage is given by the partial pressure ratio of the thermistor and a resistor connected in series. A voltage given to one input of the first voltage comparator 61, a voltage generator, and a voltage given by the voltage division ratio of the volume and the series resistor to the other input of the first voltage comparator 61, and used as a reference voltage. The output of the first voltage comparator controls the operation and stop of the water heater to adjust the temperature, and the voltage given by the voltage division ratio of the thermistor and the series resistor is applied to one of the second voltage comparators. A voltage given by the voltage division ratio of a series resistor is applied to the other input of the voltage comparator as a reference voltage, a resistor is connected to the input, and a square wave oscillation signal is connected to the other end of the resistor. is applied to change the reference voltage into two voltages, and the output thereof is used to detect over-rise and disconnection of the thermistor.

The present invention has the above-mentioned configuration, so that even if the resistor that provides the reference voltage for the over-rise detection comparator is disconnected, the temperature control comparator operates to stop combustion before over-rise detection is detected. . Alternatively, even if the resistor that provides the reference voltage for the temperature control comparator is disconnected, overheat detection is activated and combustion is stopped. Therefore, it is possible to solve the problem that when one resistor starts to break, temperature control and excessive rise detection do not operate and combustion goes out of control.

Description of examples Hereinafter, one embodiment of the present invention will be described based on the drawings.

In FIG. 2, a thermistor 21 detects the water temperature inside the can, and a resistor 22 and a resistor 23 are connected in series and in parallel, respectively. The voltage at the connection point between the thermistor 21 and the resistor 22 is inversely proportional to the temperature of the thermistor 21, and as the temperature increases, the voltage decreases.

This voltage is applied to the inverting input of a comparator 35 that performs temperature control and a comparator 36 that performs over-rise detection and disconnection detection. The non-inverting input of the temperature control comparator 36 has a voltage generated by the voltage division ratio between the resistor 29, resistors 3o and 31 connected in series via a remote control cable 37, and a volume 32 connected in parallel to the resistor 3o. 4 can be seen. This voltage becomes the reference voltage for temperature adjustment, and by changing the volume 32, the reference voltage can be changed and the setting of the boiling water temperature can be changed. Resistor 27 is a feedback resistor that provides a differential for temperature control, and 28 is a pull-up resistor. a resistor 26 connected in series with the resistor 25; and a resistor 24 whose one end is connected to the connection point between the resistors 26 and 26 and whose other end is connected to the microcomputer 38.
The voltage given by the voltage division ratio of the resistor 26 and the resistors 24 and 26 is applied to the non-inverting input of the comparator 36 that detects over-rise and disconnection, and is used as the reference voltage for over-rise detection and disconnection detection. Become. 33 is a feedback resistor that provides a differential for over-rise detection and disconnection detection, and 34 is a pull amplifier resistor. One end of the resistor 24 is connected to an output port of a microcomputer 38, and the microcomputer 38 switches this output between a high level and a low level at regular intervals. Therefore, when the output is at a low level, it is equivalent to connecting the resistor 24 in parallel with the resistor 25, and the reference voltage becomes low. This voltage becomes the reference voltage for over-rise detection. Figure 4 shows an equivalent circuit.

- When the power output is at a high level, the resistor 24 is equivalent to being connected in parallel with the resistor 26, and the reference voltage becomes high. FIG. 5 shows an equivalent circuit.

This voltage becomes the reference voltage for disconnection detection. FIG. 3 shows the waveform of the output of the microcomputer 38.

The operation in the above configuration will be explained. First, thermistor 21
When a disconnection failure occurs, a voltage equal to the voltage division ratio of the resistor 22 and the resistor 23 is applied to the inverting input of the over-rise and disconnection detection comparator 36. This voltage is higher than when the thermistor 21 is not disconnected. microcomputer 3
When the output of 8 is at a high level, the reference voltage of the comparator 36 becomes high. However, this reference voltage is lower than the voltage applied to the inverting input of the comparator 36 when the thermistor 21 is disconnected. Therefore, the output of the comparator 36 is at a low level, and the microcomputer 38 detects the disconnection of the thermistor 21.

The input port of the microcomputer 38 to which the output of the comparator 36 is input judges the input in synchronization with the output of the output port. In other words, if the input port is high level 9/z・le when the output port is high level, it is normal. If it is low level, disconnection is detected. When the output port is at low level, if the input port is at high level, over-rise is detected.
The software is configured so that if the level is low, it is determined to be normal.

If thermistor 21 is normal, thermistor 21'
As the temperature of the temperature regulator 360 increases, the inverting input voltage of the temperature control comparator 360 decreases. When the voltage becomes lower than the reference voltage set by the volume 32 applied to the non-inverting input, the output of the comparator 36 reaches a high level, and the microcomputer 38ij determines that it is a boiling signal and stops combustion.

If for some reason there is no boiling signal, combustion continues, the temperature of the thermistor 21 continues to rise, and the inversion input given to the comparator 36 continues to decrease. When the output of the microcomputer 3 is at the low level, the non-inverting input voltage of the comparator 16 becomes low and becomes the reference voltage for over-rise detection.

When the inverting input voltage of the comparator 36 becomes lower than the non-inverting input voltage, the comparator 36 outputs a high level, and the microcomputer 38 detects an excessive rise in the voltage of the 101-mister 21.

Effects of the Invention As described above, according to the present invention, the temperature change of the thermistor is converted into a voltage signal, and the voltage signal is applied to the temperature control comparator and the comparator for over-rise detection and disconnection detection, and each reference voltage is connected to a separate resistor. By applying this at the side, the problem of runaway combustion occurring because both the temperature control and overheat detection functions do not work due to one resistor being disconnected can be solved.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a conventional example, Fig. 2 is a circuit diagram showing an example of an embodiment of the present invention, Fig. 3 is a signal waveform diagram of an output port of a microcomputer, and Figs. 4 and 5 are FIG. 2 is an equivalent circuit diagram of filtration rise detection and disconnection detection configured by the output of a microcomputer. 14... Power transformer, 16-... Rectifier diode bridge, 16... Zener diode, 17° 18... Capacitor, 19...
...Current limiting resistor, 36...Comparator (
1st voltage comparator), 36... comparator (
second voltage comparator), 39...constant voltage power supply, 4
o~42...Noise prevention capacitor. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure Q/

Claims (1)

[Claims] a thermistor for detecting the temperature of water inside the can of the water heater, a voltage given by a voltage division ratio of the thermistor and a resistor connected in series is applied to one input of the first voltage comparator; The voltage given by the voltage division ratio of the volume and the series resistor is applied to the other input of the voltage comparator, and this is used as the reference voltage.
The output of the first voltage comparator controls the operation and stop of the water heater to adjust the temperature, and the voltage given by the voltage division ratio of the thermistor and the series resistor is input to one side of the second voltage comparator. A voltage given by the voltage division ratio of the series resistor is applied to the other input of the second voltage comparator, and a resistor is connected to the input of the reference voltage. A water heater control device configured to apply a wave oscillation signal to change a reference voltage into two voltages, and use the output to detect an over-rise in the thermistor and a disconnection.