JPH0121421B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a temperature control device for a water heater.

FIG. 1 is a schematic diagram of a water heater using a gas proportional valve that proportionally controls the amount of gas supplied to a burner according to the amount of current. In other words, the water heater includes a gas burner 2 to which gas is supplied through a gas pipe 1, heated by the combustion heat of this gas burner 2, and heat exchanged with water that is integrated with a water pipe 3 and flows in from the water pipe 3. The exchanger 4, a temperature sensing element 5 such as a negative characteristic thermistor that detects the hot water temperature, which is installed on the heat exchanger outlet side of the water pipe 3, and the temperature at which the signal of this temperature sensing element 5 and the signal of the temperature setting device are input. Temperature control device 6 of control device 6
It basically consists of a gas proportional valve 7 provided in the gas pipe 1, and the gas proportional valve is activated by the signal detected by the temperature sensing element 5, thereby causing the gas burner 2 to The temperature of the water coming out of the faucet 8 is maintained at a predetermined temperature by controlling the amount of gas supplied. A flow switch 9 is attached to the water pipe 3, and the power to the temperature control device 6 is turned on and off by the flow switch 9 for purposes such as power saving.

As described above, a conventional temperature control device that adjusts the temperature of hot water by controlling the amount of gas burned in a gas burner using a gas proportional valve has a circuit configuration as shown in FIG. 2, for example. That is, 10 is a power switch that opens and closes a DC power supply connected to the circuit, and a flow switch 9 attached to the water pipe.
The circuit closes when there is water flow in the water pipe. 11 is a temperature sensing element such as a negative characteristic thermistor that detects the water temperature; 12 is this temperature sensing element 11;
A temperature setting device consisting of a variable resistor etc. connected to
13 is a reference voltage obtained by dividing the power supply voltage with a resistor, etc.; 14 is a detector consisting of an operational amplifier that detects the difference between the hot water temperature and the set temperature; The connection point with the reference voltage 13 is connected to its negative input terminal, and the reference voltage 13 is connected to its positive input terminal. This detector 14
If the temperature detected by the temperature sensing element is lower than the set temperature, the output signal will be lower than the reference voltage 13, and if the detected temperature is higher than the set temperature, the output signal will be higher than the reference voltage 13, When the detected temperature matches the set temperature, the output signal operates to match the reference voltage 13. 15 is an operational amplifier, and the output signal of the detector 14 is connected to the resistor 1.
6 to its negative input terminal, and a reference voltage 13 to its positive input terminal.
Reference numeral 17 denotes a control transistor controlled by the output signal of the operational amplifier 15. Its emitter side is connected to ground via a resistor 18 for coil current detection, and its collector side is connected to the ground via the excitation coil 19 of the gas proportional valve 8. It is connected to a power source and controls the current flowing through the excitation coil 19. A capacitor 20 is connected between the negative input terminal of the operational amplifier 15 and the emitter of the control transistor 17, and together with the operational amplifier 15, the resistor 16, and the control transistor 17, constitutes a Miller integrator. 21 is a diode for absorbing back electromotive force generated in the exciting coil 19. Due to the presence of the integral circuit, the temperature control circuit configured in this manner can draw out hot water at a stable temperature as long as the water heater is used in a steady state. However, water heaters are generally used intermittently at a predetermined set temperature, and in that case, conventional temperature control circuits do not allow the water heater to restart after turning off the hot water faucet and stopping water supply, as shown in Figure 3. Immediately after starting hot water supply, the temperature of the hot water suddenly drops, causing an inconvenience to the user. This phenomenon occurs for the following reasons.
That is, when hot water supply is stopped, the power switch 10 is opened by the operation of the flow switch 9, and the power supply voltage is not supplied. As a result, the charges that have been charged in the integrating capacitor 20 forming the integrating circuit are discharged through the resistor 18. In this state, when the flow switch operates again and the power switch 10 is closed, the current flowing through the control transistor 17 becomes small until a predetermined charge is charged to the integrating capacitor 20, so that the current is supplied to the burner 2. The amount of gas flowing into the water decreases, and as a result, the temperature of the water decreases. After a predetermined charge is charged to the integral capacitor 20, the water temperature returns to the predetermined set temperature.

The present invention aims to provide a water heater temperature control device that eliminates the disadvantages of conventional temperature control circuits and can always supply hot water at a stable temperature even during frequent intermittent use. The purpose and gist thereof is that even if the power to the control circuit is cut off, the integral capacitor of the integrating circuit stores the integral amount.

An embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 4, reference numerals 10 to 21 are the same as the configuration of the conventional example described in FIG. 2, so the explanation thereof will be omitted by citing the same reference numerals.
Reference numeral 22 denotes a switching means provided in the discharge path of the integrating capacitor 20, which operates in synchronization with the power switch 10. That is, when the hot water faucet is closed and hot water supply is stopped, the switching means 22 simultaneously opens the power switch 10, and when hot water supply starts, the switching means 22 is operated to close the circuit. Such a switching means 22 can be integrated with a flow switch so as to be interlocked with the power switch 10, or it can be constituted by a separate relay, but a more practical one is shown in FIG. A circuit configuration like this is adopted.
That is, a transistor 23 is connected in series to the discharge path of the integrating capacitor 20, and a transistor 26 is provided which is operated by a voltage obtained by dividing the voltage across the coil current detection resistor 18 by voltage dividing resistors 24 and 25.
This transistor 26 is connected to the base circuit of the transistor 23 via a base resistor 27. The switching means configured in this manner operates as follows. In other words, when the hot water faucet is opened and the power switch 10 is closed, the current of the exciting coil 19 flows through the resistor 18, causing a voltage drop, and the resistors 24, 2
The transistor 26 is turned on by the divided voltage of 5.5. Then, due to the presence of the base resistor 27, the transistor 23 becomes conductive, and the switching means becomes closed. However, when the hot water faucet is closed and the power switch 10 is opened, no current flows through the resistor 18, so the transistor 26 is not conductive, and as a result, the transistor 23 is also rendered non-conductive, and the switching means is opened. state.

In this way, the temperature control circuit provided with the switching means in the discharge path of the integrating capacitor does not change the integrated amount of the integrating capacitor 20 even if the power switch is turned off. Even if you start hot water supply again after stopping it, the water temperature will hardly change.

Although the temperature control circuit for a water heater according to the present invention is constructed as described above, it is not necessarily limited to the above embodiment, and various modifications can be made. For example, the integrating circuit is not limited to the Miller integrator as described above, but may be an integrator having another circuit configuration. In short, it is sufficient that the configuration is such that the charge in the integrating capacitor is discharged when the power switch of the control circuit is turned off.
Furthermore, a proportional circuit and a differential circuit can be added to the above-mentioned integrating circuit, if necessary.

As explained above, the water heater temperature control device of the present invention is configured such that the integral capacitor stores the integral amount even if the power to the control circuit is cut off. This provides an excellent effect in that the water temperature does not change and cause discomfort to the user.

[Brief explanation of drawings]

Figure 1 is a system diagram for explaining temperature control of a water heater, Figure 2 is a conventional temperature control circuit diagram, and Figure 3 is a diagram of a conventional temperature control circuit.
FIG. 4 is a temperature control circuit diagram of an embodiment of the present invention, FIG. 5 is a circuit diagram of a switching means used therefor, and FIG.
The figure is a diagram showing changes in hot water temperature caused by the temperature control circuit of the present invention. 10...Power switch, 11...Temperature sensing element, 1
2...Temperature setting device, 13...Reference voltage, 14...
Detector, 15... operational amplifier, 16, 18... resistor, 17... control transistor, 19... exciting coil, 20... integrating capacitor, 21... diode, 22... switching means.

Claims (1)

[Claims] 1. Based on the output signal from the detector that detects the difference between the temperature of the water heated by the heat exchanger and the set temperature,
In a temperature control device for a water heater that controls a gas proportional valve through a control circuit including at least an integral circuit, an integral capacitor of the integral circuit stores the integral amount even if the power to the control circuit is cut off. A water heater temperature control device characterized by: 2. A patent that provides a switching means that operates in synchronization with the power switch of the control circuit in the discharge path of the integrating capacitor, so that the integrating capacitor memorizes the integral quantity even if the power of the control circuit is cut off. A temperature control device for a water heater according to claim 1.