JPH0220607Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a proportional control device for water heaters, particularly instantaneous water heaters.

Conventionally, in order to control the outlet temperature of hot water to a set temperature in an instantaneous water heater, as shown in FIG. A controller 4 is provided which compares and calculates the signal of The amount of hot water was adjusted so that hot water was dispensed at a set temperature. Conventionally, in many cases, the controller 4 includes a proportional element that amplifies the deviation between the signal of the temperature sensor 2 and the signal of the setting device 3.
It consists of a differential element that amplifies the amount of change in the signal, and an integral element that temporally corrects the deviation. By the way, the optimum values of the constants of the proportional, integral, and differential elements differ depending on the tapping temperature (for example, 40°C and 80°C), and the time constant of the integral element in particular has a very large effect on the tapping characteristics. That is, if the time constant of the integral element is made small, the output becomes unstable and oscillates near the set value, whereas if the time constant is made large, it takes time to reach the set value.

Taking the above problems into consideration, the present invention has developed a proportional control device for water heaters that changes these constants in accordance with changes in the temperature of hot water to provide stable hot water with good transient characteristics such as rising water. The configuration of the present invention will be specifically explained below based on an illustrated embodiment. In the example shown in Figure 2, only the time constant of the integral element among the proportional, integral, and differential elements is changed, but this is because the influence of this time constant has a large weight on the hot water dispensing characteristics. The amplification factors of each proportional and differential element may also be changed. The control unit 4 is provided with a bridge circuit A in which a thermistor 7 constituting the temperature sensor 2, a variable resistor 8 which is varied by the setting operation of the setting device 3, and fixed resistors 9 and 10 are provided on one side, respectively. Midpoint A between device 8 and thermistor 7
is connected to an inverting input terminal via resistors 11 and 12, and a midpoint b between fixed resistors 9 and 10 is connected to a non-inverting input terminal via a resistor 13;
The output terminal of the integrating amplifier 14 is connected to resistors 15 and 16.
The middle point a of the bridge circuit A is connected to the inverting input terminal through the resistor 17 and the differential capacitor 1.
A parallel circuit 19 with 8 and a proportional amplifier 21 connected to the non-inverting input terminal via a resistor 20 are provided. Furthermore, 22 is an integrating capacitor, and 23 is a resistor 1.
This positive characteristic thermistor 23 is connected in parallel with the temperature sensor 2 and in series with the integrating capacitor 22. Like the temperature sensor 2, the positive characteristic thermistor 23 is designed to detect the water temperature. Further, in the gas proportional valve 6 described above, the valve coil current value is controlled in accordance with the output of the proportional amplifier 21, so that the amount of gas supplied to the gas burner 5 is adjusted.

In the above configuration, when hot water starts to be dispensed, if the hot water temperature is lower than the set temperature, the integral condenser 22
Charging is performed with the polarity shown in the figure, and the output of the integral amplifier 14 decreases.On the other hand, the midpoint a potential of the bridge circuit A is at a high potential, so the proportional amplifier 21 is charged with the polarity shown in the figure. The difference is widened and the coil current of the gas proportional valve 6 is increased to increase the combustion capacity of the gas burner 5. Conversely, when the hot water temperature is higher than the set temperature, the above-mentioned integral output increases and the combustion capacity of the gas burner 5 is increased. In this way, the combustion capacity of the gas burner 5 is adjusted according to the water temperature, and the water temperature is maintained at the set temperature.

By the way, the influence of the integral time constant when carrying out proportional/integral (+derivative) control in this manner is as described above, and therefore setting this time constant has been extremely difficult in the past.

However, according to the present invention, the integrating capacitor 22
A positive characteristic thermistor 23 is connected in series with the positive characteristic thermistor 23 so that the resistance value that determines the integral time constant can be varied according to the water temperature, so when the water temperature is high, the time constant becomes large. On the other hand, when the water temperature is low, the time constant is automatically set to a small value, and integration is performed with the optimal time constant for each temperature. There is no hunting or delay in rising, and hot water can be dispensed smoothly.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, and FIG. 1 is a schematic diagram of an instantaneous water heater, and FIG. 2 is an electric circuit diagram. 1...Heat exchanger, 2...Temperature sensor, 3...
Setting device, 4... Controller, 5... Gas burner, 6...
...Gas proportional valve, 23...Positive characteristic thermistor.

Claims (1)

[Scope of utility model registration request] Deviation between the heat exchanger, the gas burner that heats the heat exchanger, the gas proportional valve installed in the gas passage to the gas burner, the signal from the temperature sensor that detects the hot water temperature, and the signal from the setting device that changes the hot water temperature. and a controller that controls the gas proportional valve by proportionally integrating the
A control device for a water heater in which the integral time constant of the controller is varied by connecting a positive characteristic thermistor for detecting water temperature to the integral time constant circuit so that it is greater when the water temperature is high and smaller when the water temperature is low.