JPS6124608B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas water heater that makes the combustion amount variable and controls the temperature of hot water, and particularly to reduce overshoot when changing the flow rate.

BACKGROUND ART Conventionally, there is a gas water heater using a burner with a variable combustion rate, in which the combustion rate in the gas burner is controlled by combining, for example, a mixing tube, a zero governor, and a blower fan. In this case, the outlet temperature is detected by some method, the speed of the blower fan is controlled according to this output, the pressure difference generated in the mixing tube is controlled, and the zero governor controls the gas flow rate according to this pressure difference. Although this makes it possible to control the temperature of hot water, the following problems arise. In other words, due to the relatively large time constant of the blower fan and the heat capacity of the heat exchanger, the so-called overshoot that occurs when the hot water output is suddenly changed from a relatively large flow rate to a relatively small flow rate is large, resulting in burns, etc. This led to a dangerous situation.

The present invention eliminates such conventional drawbacks, and embodiments thereof will be described below with reference to the accompanying drawings.

In Fig. 1, the main body 1 has a gas burner 2, gas G passes through a solenoid valve 3 and a zero cabana 4 to a mixing pipe 5, and air A passes through an air supply pipe 6 to the mixing pipe 5, where they are mixed and sent to the burner 2. Inflow. The water W passes through the water supply pipe 7, undergoes heat exchange in the heat exchanger 8, and is then supplied as hot water H through the hot water outlet pipe 9. The hot water temperature is detected by the hot water temperature detector 10 and input to the controller 12, and the controller 12 controls the fan motor 11 and turns on/off the solenoid valve 3 according to the input. The combustion exhaust gas is sucked and discharged as E from the main body 1 by the fan motor 11.

FIG. 2 shows a block diagram of the controller 12, in which a signal from the temperature detector 10 is input, and the proportional and differential values of the temperature signal are taken by a proportional differentiator 12A. The output of the proportional differentiator 12A is input to the phase control circuit 12B and the solenoid valve control circuit 12C, the phase control circuit 12B controls the speed of the fan motor 11, and the solenoid valve control circuit 12C turns the solenoid valve 3 on and off.

When the amount of hot water suddenly changes from a large flow rate to a small flow rate, the temperature of hot water rises transiently. Hot water temperature detector 10
is detecting the outlet hot water temperature, and its output is input to the comparison differentiator 12A. The output is a signal proportional to the difference between the set temperature and the hot water temperature, and a differential value of the difference. Therefore, if the hot water temperature rises transiently and rapidly, its differential value will increase,
Based on this differential signal, the solenoid valve control circuit 12C outputs an off signal to turn off the solenoid valve 3. Since the combustion amount becomes zero, the hot water temperature decreases. After an appropriate period of time has elapsed, the solenoid valve 3 is turned on again to start combustion, and the temperature of the hot water will settle down to a steady value. In this way, overshoot is reduced.

FIG. 3 is a specific circuit example of the block diagram of FIG. 2. 13 is stepped down with a transformer _D1 , full-wave rectified with a rectifier bridge _D2 , clipped with a Zener diode _D3 via a current limiting resistor _D6 , and connected to the DC power supply _Vz of the phase control circuit 12B. do. _{Let Vz} be the backflow prevention diode _D5 , and the voltage _Vcc smoothed by the capacitor be the DC power supply voltage of the proportional differentiator 12A and the electromagnetic valve control circuit 12C. 10
is a thermistor as a hot water temperature detector, and is a resistor.
Divide A ₁ and V _cc to obtain the voltage V _t . V _t corresponds to the hot water temperature. The voltage _VR obtained by dividing _Vcc by the resistors A ₂ and A ₃ is the reference voltage. capacitor
A ₅ , resistors A ₄ , A ₆ , and operational amplifier A ₇ constitute a proportional differential circuit, and its transfer function is given by -R ₆ /R ₄ (1 + R ₄ C ₅ S). Here R ₄ and R ₆ are resistances
The resistance values of A ₄ and A ₆ , and C ₅ are the capacitance of capacitor A ₅ . The input voltage V _Ai is (V _R -V _t ), and the output V _AO is the proportional + differential value of V _i . _VAO becomes the input of two circuits. The first is a phase control circuit 12B, and the second is a solenoid valve control circuit 12C. Phase control circuit 12
B basically consists of PUTB ₄ and triax B ₈ , and _VAO is the control input. With the transistor B ₂ and the resistor B ₁ , the collector current I _C2 of the transistor B ₂ can be expressed as I _C2 = V _z −V _AO −V _BE2 /R _B1 . Here, V _BE2 is the base-emitter voltage of the transistor B ₂ and R _B1 is the resistance value of the resistor B ₁ .
The charging rate of capacitor _B3 is proportional to I _C2 . When the voltage V _C3 of capacitor B ₃ becomes higher than the voltage V _G obtained by dividing V _z by resistors B ₅ and B ₆ , PUTB ₄ turns on, and the discharge current of capacitor B ₃ flows through PUTB ₄ to the primary transformer B ₇ . This current turns on triac _B8 . If V _AO is low, I _C2 is large, V _C3 reaches V _G quickly, the phase at which the triax B ₈ is turned on is early, the voltage applied to the motor 11 is also large, and the fan rotates at high speed. When the tapped water temperature becomes lower than the set temperature, V _t becomes large, V _Ai becomes negative, V _AO becomes small, the fan rotates at high speed, increases the combustion amount, and raises the tapped hot water temperature.

The solenoid valve control circuit 12C connects V A to a series circuit of capacitor C ₁ , resistors C ₂ and C ₃ in order to obtain the differential value of V _{AO .}
Enter _O. Voltage V _p divided by resistors C ₂ and C ₃
becomes the positive input of the comparator _C24 , and its negative input is the voltage _VN obtained by dividing _Vcc by the resistors _C4 and _C5 .
If the differential value is small and V _P < V _N , the comparator
The output of C ₂₄ is zero. When V _P > V _N , the output of comparator C ₂₄ becomes high, and this change passes through capacitor C ₆ and diode C ₈ to resistor C ₉ ,
A monostable multivibrator consisting of C ₁₀ , C ₁₁ , C ₁₅ , C ₂₄ , capacitor C ₁₂ , diode C ₁₃ , Zener diode C ₁₄ , and operational amplifier C ₁₆ is triggered.
This monostable multivibrator operates as follows. When there is no output from the comparator C ₂₄ , the zener voltage V _z of the zener diode C ₁₄ is input to the negative input of the operational amplifier C ₁₆ , and the current voltage V _cc is input to the positive input of the resistor C ₉ and the resistors C ₁₀ and C ₂₅ The voltage V ⁺ obtained by dividing the voltage by parallel connection is input. Now if V _z > V ⁺ , the output V _n of the operational amplifier C ₁₆ is low V _nL ≒
Becomes OV. From this state, when the output of comparator C ₂₄ goes high, the positive input of operational amplifier C ₁₆
The voltage of V ⁺ plus the output of comparator C ₂₄
V', V'>V _z , and the output V _n of the operational amplifier C ₁₆ becomes high V _nH . Output V _n of operational amplifier C ₁₆
becomes high V _nH , its positive input is V _nH = V
_cc , the voltage obtained by dividing the power supply voltage V _cc by the parallel connection of resistors C ₉ and C ₁₀ and the resistor C ₂₅ becomes V _H ⁺ >V _z , and the output of the operational amplifier C ₁₆ maintains high V _nH . On the other hand, after the output of the operational amplifier C ₁₆ becomes high V _nH , its negative input gradually increases through the resistor C ₁₁ to the capacitor C ₁₂ from the zener voltage V _z to the power supply voltage V _cc . When the predetermined time T _n has elapsed, the voltage of the capacitor C ₁₂ , that is, the operational amplifier C ₁₆
The negative input of becomes V ^- > V _H ⁺ and the output of op amp C ₁₆ becomes low V _nL again. As a result, the positive input of the operational amplifier C ₁₆ becomes V ⁺ <V _z again. On the other hand, the voltage across capacitor _C12 , which is the negative input of operational amplifier _C16 , is
Since the output of operational amplifier _C16 is low V _nL , it is zero V
The zener diode C ₁₄
, so the zener voltage V _z
The descent stops. As detailed above, this monostable multivibrator is a comparator
When the output of C ₂₄ changes from low to high, it is triggered and outputs high V _nH for a predetermined time T _n . This signal causes a base current to flow through the transistor C ₁₈ via the current-limiting resistor C ₇ , turning on the transistor C ₁₈ , causing current to flow through the relay coil C ₁₉ , and turning off its normally closed contact for a predetermined period of time. Therefore, no power is supplied to the solenoid valve coil 3, and the solenoid valve 3 is turned off for a predetermined period of time.
When the monostable multivibrator output becomes high V _nH , this is the diode C ₂₀ , resistor C ₂₁ , and capacitor
It is input to the inhibition circuit consisting of _C23 . That is, the output V _nH is a capacitor C ₂₃ connected to the negative input of a comparator C ₂₄ via a diode C ₂₀ and a resistor C ₂₁ .
to charge. The monostable multivibrator output becomes low V _nL again after a predetermined time, but the comparator
The negative input of C ₂₄ charges capacitor C ₂₃ to V _nH while the monostable multivibrator output is high, discharging relatively gently through resistor C ₂₂ . During the period in which the negative input of the comparator is greater than V _N , the original function of the comparator C ₂₄ , which is to compare the input differential signal with V _N , is lost, and its operation is prohibited.

Assume that the control system is stable with a relatively large amount of hot water coming out. Therefore, when the amount of hot water suddenly changes to a relatively small amount, the resistance of the thermistor 10 quickly decreases.
This is because the temperature of the hot water increases. V _t
becomes smaller, so _VAO becomes larger. At the same time, the differential value of the temperature change also appears in V _AO , and V _AO becomes extremely large. Since V _AO rises in a short time, this change is divided by resistors C ₂ and C ₃ via capacitor C ₁ , and the voltage V _P exceeds V _N and the solenoid valve 3 is closed for a predetermined time.
Turn off. When the solenoid valve 3 is turned off, the temperature of the hot water drops. However, in some cases, it drops too much and the V _AO drops quickly to increase the motor speed again, causing the tap water temperature to rise. But if it rises too high again here, the differential input will be the comparator C ₂₄
becomes a positive input, and attempts to turn off the solenoid valve 3 for a predetermined period of time. Hello, once the comparator
After the operation of C ₂₄ , unless the operation of comparator C ₂₄ is prohibited, the solenoid valve 3 is turned off. By repeating the above operations, the solenoid valve 3 regularly repeats the on/off operation, and the temperature of the tapped water oscillates with a relatively large amplitude. In other words, this leads to an oscillation phenomenon. However, in the present invention, such oscillation phenomenon is eliminated by the comparator.
It can be effectively avoided by prohibiting the operation of _C24 .

As detailed above, since the solenoid valve is turned off depending on the input differential signal, that is, the magnitude of change in the tapped water temperature, overshoot when changing the flow rate can be reduced. Furthermore, since the comparator operation is prohibited for a predetermined period of time after it has been operated once, the oscillation phenomenon that occurs when the solenoid valve is turned off is no longer observed.

According to the present invention, the hot water temperature control of a gas water heater in a system having a relatively large time constant can be performed with little overshoot and without oscillation.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram of a gas water heater according to an embodiment of the present invention, Fig. 2 is a block diagram of the control section, and Fig. 3 is a block diagram of the control section.
The figure is an electrical circuit diagram. 2... Gas burner, 3... Solenoid valve, 8... Heat exchanger, 10... Temperature detector, 12... Controller, 1
2A...Proportional differential circuit, 12C...Solenoid valve control circuit.

Claims (1)

[Claims] 1 a gas burner, a heat exchanger, and a gas flow rate control device that controls the amount of combustion in the gas burner;
A solenoid valve provided in the gas circuit that turns on and off the inflow of gas to the gas burner, a temperature detector that detects the hot water temperature, and a gas flow control device and the solenoid valve according to the output of the temperature detector. The controller includes a differentiating circuit that differentiates the output of the temperature sensor, a comparator whose output is inverted depending on the polarity and magnitude of the output of the differentiating circuit, and a monostable multifunction device that is triggered by the output of the comparator. a vibrator, a switch circuit that turns off the power supply to the solenoid valve by the output of the monostable multivibrator;
A gas water heater comprising a solenoid valve control circuit configured with a prohibition circuit that prohibits operation of a comparator by the output of the monostable multivibrator.