JPH058331B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a gas instantaneous water heater to which so-called feedforward control is applied, which adjusts the amount of gas according to the amount of water, set temperature, and water supply temperature.

Prior Art Conventional technology for this type of gas instantaneous water heater includes, for example, Japanese Patent Application No. 53-150227. In the conventional example, based on the signals from the temperature setting device that sets the hot water temperature, the water supply temperature sensor, and the water flow sensor, the gas volume = K x water volume x (set temperature - water supply temperature)
...Formula 1 Here, K is determined by calculating the proportionality constant, but since the above calculation requires multiplication, it is input using an analog multiplier or a microcomputer. In many cases, signals are converted from analog to digital and numerical calculations are performed, making the configuration of the control circuit complex and increasing costs.

Problems to be Solved by the Invention The present invention aims to solve the problems in the prior art, and aims to reduce the cost of the control circuit in the application of feed forward control, and to improve the stability of hot water temperature at low cost. The aim is to provide an excellent gas instantaneous water heater.

Means for Solving the Problems In order to achieve this object, the present invention provides a water flow sensor that generates a frequency signal proportional to the amount of water supplied to a heat exchanger, a temperature setting device that sets the hot water temperature, and a water supply temperature a one-shot circuit that is activated by the frequency pulse signal of the water flow sensor and outputs a pulse width proportional to the difference between the set temperature and the water supply temperature, and a filter circuit that smoothes the output signal of the one-shot circuit. , and a gas proportional control valve that is driven by the output of the filter circuit and adjusts the amount of gas supplied to the burner.

Effect In the above configuration, the output of the one-shot circuit is a pulse train with a pulse width proportional to the difference between the set temperature and the water supply temperature, and a frequency proportional to the water supply amount, and the smoothed average value of the pulse train is equal to the water supply amount x ( A value proportional to (set temperature - supply water temperature) is obtained, and based on the feed forward calculation shown in Equation 1, it acts so that the amount of gas corresponding to the required amount of heat is supplied.

Embodiment Next, an embodiment of the present invention will be described in detail with reference to the drawings. In FIG. 1, a heat exchanger 2 heated by a burner 1, a water amount sensor 3 and a water supply temperature sensor 4 provided in a water supply channel of the heat exchanger 2, and a gas supply channel provided in a gas supply channel to the burner 1 are shown. Proportional control valve 5
The output pulse width is adjusted by inputting the difference between the signals of the temperature setting device 6 and the temperature setting device 6 and the feed water temperature sensor 4, and the one shot circuit 7 triggered by the signal of the water amount sensor 3 and its output are smoothed. The gas proportional control valve 5 is driven by the output of the filter circuit 8 . In FIG. 2, the one-shot circuit 7 includes a flip-flop 10 that is set by a pulse from a water sensor and reset by a comparator 9, a constant current source 11 connected to a non-inverting input 9a of the comparator 9, a charging capacitor 12, and a charging/discharging control transistor 13. has
The base of the charge/discharge control transistor is driven by the inverted output of flip-flop 10. Further, the midpoint voltage of the bridge consisting of the temperature setting device 6 (volume) and the feed water temperature sensor 4 (thermistor) is applied to the inverting input 9b of the comparator 9. The inverted output of flip-flop 10 is applied to the base of drive transistor 14, which switches DC power supply 15 to drive the electromagnetic coil of gas proportional control valve 5 through filter circuit 8 consisting of resistor 16 and capacitor 17.

In the above configuration, when the flip-flop is set by a pulse from the water level sensor 3, its inverted output becomes a low level, the charge/discharge transistor 13 is turned off, and the charging capacitor is charged at a constant voltage increase rate by the constant current source 11, and the inverted input 9b
When the voltage becomes equal to the voltage, the outputs of the comparators 9 and 9 become high level, and the flip-flop 10 is reset. Here, the charging/discharging transistor 13 is turned on again to discharge the charge in the charging capacitor 12 and return to the initial state. That is, since the voltage at the inverting input 9b has a value proportional to the difference between the set temperature and the water supply temperature, the output pulse width of the flip-flop 10 has a value proportional to (set temperature - water supply temperature). In Fig. 3, when the water supply amount changes with time on the horizontal axis as shown in a in the same figure, the water amount sensor detects that the period τwi is the water amount.
A pulse train is generated that is inversely proportional to Qw.

τwi=K ₁ × 1/Qw K ₁ ...Proportionality constant ...Formula 2 As mentioned above, the output of the one-shot circuit 7 is a pulse train synchronized with the water flow sensor pulse with a pulse width τT proportional to the difference between the set temperature Ts and the water supply temperature Twi. becomes.

τT=K ₂・(Ts−Twi)K ₂ ...Proportionality constant ...Formula 3 The drive transistor 14 is connected to the voltage Vcc of the DC power supply 15
The voltage Vd applied to the gas proportional control valve 5 via the filter circuit 8 is the average value of the drive pulses, and Vd=Vcc×τT/τwi=Vcc×K ₂ /K ₁ ×Qw×(Ts−Twi
)=K×Qw×(Ts−Twi) Equation 4 It can be seen that Equation 4 performs the feed forward operation shown in Equation 1. As shown in Fig. 3c, the average amount of gas is supplied to provide the required amount of heat in accordance with the amount of water supplied. When the set temperature becomes lower or the water supply temperature becomes higher, the one-shot circuit output pulse width becomes shorter to τT' as shown in FIG. 3d, and the average gas amount becomes smaller accordingly.

Effects of the Invention As described above, the gas instantaneous water heater of the present invention includes a water flow sensor that generates a frequency signal proportional to the water supply amount, a temperature setting device that sets the hot water temperature, and a water supply temperature that detects the water supply temperature. It is configured to drive the gas proportional control valve through a sensor, a one-shot circuit that is activated by a signal from the water flow sensor and outputs a pulse width proportional to the difference between the set temperature and the water supply temperature, and a filter circuit that smoothes the output of the one-shot circuit. (1) Feedforward calculations can be performed without using expensive analog multipliers or microcomputers, the control circuit configuration is simple, cost reduction is significant, and an inexpensive hot water supply with good hot water temperature stability has been developed. It is possible to provide equipment.

(2) Practical water flow rate sensors are mostly based on the movement of rotating bodies such as vanes or balls rotating in water supply channels, and are suitable for the control method of the present invention. According to the authors, the output of the water flow sensor does not require signal processing such as frequency-voltage conversion or digitization by frequency measurement or period measurement, so the control circuit can be made simple and inexpensive, and errors caused by signal processing can be avoided. Therefore, highly accurate feed forward calculation is possible.

(3) The drive transistor that drives the electromagnetic coil of the gas proportional control valve operates in a switching manner, which generates much less heat than a linear control system using analog signals, and eliminates the need for a heat sink, reducing the cost of the control circuit.

It has the following effects.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of a gas instantaneous water heater according to an embodiment of the present invention, Fig. 2 is a specific circuit diagram of the same control circuit, and Fig. 3 is a schematic diagram of the same control circuit.
Figures a, b, c, and d are waveform diagrams illustrating the operation of the same circuit. 1...Burner, 2...Heat exchanger, 3...Water flow sensor, 4...Incoming water temperature sensor, 5...Gas proportional control valve, 6...Temperature setter, 7 ...One shot circuit, 8 ...Filter circuit.

Claims (1)

[Claims] 1 a burner, a heat exchanger, a water amount sensor that generates a frequency signal proportional to the amount of water supplied to the heat exchanger, a water supply temperature sensor that detects the temperature of the water supply, a temperature setting device that sets the hot water temperature; A gas proportional control valve that adjusts the amount of gas to the burner, and a one-shot circuit that is activated by a signal from the water amount sensor and outputs a pulse width proportional to the difference between the set temperature of the temperature setting device and the feed water temperature of the feed water temperature sensor. and a filter circuit that smoothes the output pulse of the one-shot circuit and drives the gas proportional control valve.