JPH0447215B2 - - Google Patents

Description

[Detailed Description of the Invention] <<Field of the Invention>> This invention digitally performs PID calculation using a microcomputer based on the hot water exit temperature and the set temperature, and controls the fuel gas supply amount based on the calculation result to adjust the hot water exit temperature. The present invention relates to a temperature control device for a gas water heater that maintains water at a set temperature.

<<Prior art and its problems>> In the case of the gas water heater currently under development (unpublished) by the applicant, the detected temperature detected by the hot water outlet temperature detector and the set temperature set by the hot water outlet temperature setting device Based on this, a digital PID calculation is performed using a microcomputer, and the fuel gas supply amount is controlled based on the calculation results to maintain the hot water tap temperature at the set temperature.

The basic formula for digital PID calculation used in this control is expressed by the following formula.

F=Kp×{ΔE _o +θ/T _io 〓 ⁱ⁼⁰ ΔEi +T _D /θ(ΔE _o −ΔE _o-1 )} ……(1) ΔEi=SPi−MPi ……(2) Kp; Proportional gain Ti ; Integral time T _D ; Differential time θ; Sampling time ΔEi; Deviation SPi; Set temperature MPi; Hot water temperature Note that n is the current sampling value and _o-1 is the previous sampling value.

Also, if FP, FI, and FD are proportional terms, integral terms, and differential terms, respectively, then the output F which is the result of the above calculation
is expressed by the following formula.

F=FP+FI+FD...(3) Furthermore, the integral term FI is expressed by the following equation.

FI＝Kp×θ／Ti _o 〓 ⁱ⁼⁰ ΔEi ……(4) FIn＝FI _o-1 +ΔI ……(5) FIn; Current integral value FI _o-1 ; Previous integral value ΔI; Increment (integral deviation) By the way, the integral deviation ΔI is obtained by digital calculation using a microcomputer, so if the absolute value of the deviation ΔTi between the set temperature and the hot water temperature is small, the integral deviation ΔI can be obtained by digital calculation. There are cases where it becomes zero due to rounding.

In such a case, as shown by the solid line in Figures 4 and 5, when the set temperature is increased from 40℃ to 80℃ or lowered from 80℃ to 40℃, the tap water temperature still reaches 80℃. Even though the temperature has not risen or fallen to 40℃, as mentioned above, if the deviation ΔEi between the outlet temperature and the set temperature becomes smaller than a certain value, the integral deviation ΔI will actually become zero, so the set temperature The problem arises in that the tapped water temperature reaches an equilibrium state just before the hot water temperature reaches the equilibrium state, and a so-called offset phenomenon occurs, resulting in a fixed, minute error between the tapped hot water temperature and the set temperature.

≪Object of the Invention≫ The object of the present invention is to prevent hot water from flowing even when the hot water temperature approaches the set temperature due to an increase or decrease in the set temperature, and as a result, the integral deviation becomes zero. An object of the present invention is to provide a temperature control device for a gas water heater, which allows the temperature to accurately follow a set temperature.

<<Structure and Effects of the Invention>> In order to achieve the above object, the present invention performs PID calculation based on the detected temperature detected by the hot water temperature detector and the set temperature set by the hot water tap temperature setting device. In a temperature control device for a gas water heater that maintains the hot water outlet temperature at a set temperature by controlling the fuel gas supply amount based on the calculation result, the PID calculation function includes a calculation result that is calculated and stored in a register. When the integral deviation is zero, a function is added to add or subtract a constant corresponding to the minimum bit digit of the register to the previous integral term, depending on the presence or absence and sign of the deviation between the detected temperature and the set temperature. It is characterized by the fact that

According to such a configuration, even if the integral deviation becomes zero because the tapped water temperature approaches the set temperature, a predetermined differential constant, that is, a constant value of the register for the integral term up to the previous time, is applied. By adding or subtracting the constant corresponding to the smallest bit digit, the integral term up to the previous time is increased or decreased by a small amount, and the integral term is corrected, the output increases or decreases, and the tapping temperature changes. It follows the set temperature.

<<Description of Examples>> FIG. 1 is a diagram showing a system configuration of a gas water heater according to the present invention.

In the figure, a furnace body 1 is formed into a vertical cylindrical shape, a burner 2 is arranged at the bottom thereof, a heat exchanger 3 is arranged above it, and a heat exchanger 3 is arranged at the top of the furnace body 1. An exhaust fan 5 driven by a motor M is attached to the exhaust port 4.

A water supply pipe 6 is connected to the inlet side of the heat exchanger 3, and a hot water supply pipe 7 is connected to the outlet side of the heat exchanger 3.
The hot water supply pipe 7 is branched into three pipes at the tip side, and each branch pipe 7a, 7b, 7c is attached with a collar 8a, 8b, 8c, respectively.

On the water supply pipe 6 near the inlet side of the heat exchanger 3,
A running water switch 9 is installed. This water flow switch 9 is a switch that detects and turns on when any one of the switches 8a to 8c is opened and a water flow of a certain value or more is generated in the water supply pipe 6.

On the hot water supply pipe 7 near the outlet side of the heat exchanger 3,
A hot water temperature detector 10 is attached. The hot water temperature detector 10 is composed of a temperature sensing element such as a thermistor, and is connected to a processing circuit within the controller 11 to output an analog voltage corresponding to the hot water temperature.

A gas cutoff valve 13, a gas governor 14, and a gas flow rate adjustment valve 15 are installed in this order on a gas supply pipe line 12 that supplies fuel gas to the burner 2.

The cutoff valve 13 is constituted by an electromagnetic valve that can take two states: a fully closed state and a fully open state, and is variably controlled by a signal from the controller 11.

The gas governor 14 has a function of keeping the pressure of combustion gas constant.

The flow rate adjustment valve 15 is composed of, for example, a motor-driven servo valve whose opening degree can be continuously adjusted from a fully closed state to a fully open state, and its current opening degree is determined by a potentiometer installed in the flow rate adjustment valve 15. is sent to the controller 11 side via.

The igniter 16 emits a spark in response to a command from the controller 11, and ignites the fuel gas ejected from the burner 2.

The flame detector 17 is located close to the sparks emitted from the burner 2 and uses the flame current and its rectifying action to convert the sparks into an electrical signal, and after suitably amplifying this signal, it has a relatively large time constant. It is smoothed by a smoothing circuit, further converted into a binary value with a reference level, and the output is used to drive a relay via a driver to output a contact signal.

The controller 11 is composed of a sequence circuit that controls sequence operations from the start of combustion to the stop of combustion, and a temperature control circuit that maintains the hot water temperature at a set temperature, and these circuits are composed of a microcomputer.

Temperature control is performed using the so-called PID calculation method.
As shown in FIG. 2, the deviation c is obtained based on the set temperature b set by the temperature setting device 19 and the outlet temperature a detected by the outlet temperature detector 10, and this is calculated by PID. It is functionally configured to obtain a control output amount d and to maintain the outlet hot water temperature at a set temperature by controlling the fuel gas supply amount using this control output amount d.

Here, as mentioned above, the basic formula for PID calculation is expressed by the following formula.

_{F =} ^Kp _{_ _ _} , FD are a proportional term, an integral term, and a differential term, respectively, then the control output amount F is expressed by the following equation.

F=FP+FI+FD...(3) Furthermore, the integral term is expressed by the following equation.

FI＝Kp×θ／Ti _o 〓 ⁱ⁼⁰ ΔEi ……(4) FIn＝FI _o-1 +ΔI ……(5) FIn; Current integral value FI _o-1 ; Previous integral value ΔI; Increment (integral deviation) Next, the calculation function newly added in this invention is
This will be explained based on the flowchart shown in FIG.

This calculation function calculates a predetermined differential for the previous integral term depending on the existence and sign of the deviation between the detected temperature and the set temperature, when the integral deviation calculated by calculation and stored in the register is zero. A constant, that is, a constant corresponding to the minimum bit digit of the register is added or subtracted.

That is, when the integral term calculation process is started, first in step (1), the integral deviation ΔI is calculated based on the deviation ΔEi between the set temperature and the tapped water temperature.

Note that since the calculation of this integral deviation ΔI is performed digitally by a microcomputer as described above, if the calculation result is less than a predetermined significant digit, the value of ΔI becomes zero due to rounding processing.

Next, in step (2), it is determined whether or not the obtained integral deviation ΔI is zero. If it is not zero, the process immediately proceeds to step (7), and the integral deviation is calculated for the previous integral term FI. A new integral term FI is obtained by adding ΔI.

On the other hand, if the integral deviation ΔI is determined to be zero in step (2), it is determined in step (3) or step (5) whether the deviation ΔEn between the outlet hot water temperature and the set temperature is positive or negative. will be carried out.

If it is determined to be positive, step (4) is executed and +u is stored as the integral deviation ΔI.
On the other hand, if it is determined to be negative, -u is stored as the integral deviation ΔI in step (6), and then step (7) is executed in the same manner as described above to obtain a new integral term FI.

Here, the value of the constant u corresponds to the value of the minimum bit digit of the register for storing ΔI, so this constant +u or -u can be used to calculate the previous integral term.
There is no sudden increase or decrease in FI.

When such processing is performed, Figures 4 and 5
As shown by the dotted line in the figure, even when the outlet hot water temperature approaches the set temperature and the integral deviation ΔI becomes zero, the final control output F is equal to the constant +u.
Or, it continues to increase or decrease in accordance with the increase in the integral term FI due to -u, and it is possible to prevent the occurrence of an offset state in which the set temperature and the tapped water temperature reach an equilibrium state while maintaining a certain error. This is the translation.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the system configuration of a gas water heater according to the present invention, FIG. 2 is a diagram showing an outline of PID calculation, and FIG. 3 is a flowchart showing details of integral term calculation processing according to the present invention. FIGS. 4 and 5 are graphs showing the difference in operation between the present invention and a conventional example (unpublished) previously developed by the applicant. 2... Burner, 3... Heat exchanger, 6... Water supply pipe, 7... Hot water supply pipe, 10... Hot water temperature detector,
11... Controller, 12... Gas supply pipe line,
13...Gas cutoff valve, 15...Gas flow rate adjustment valve,
19...Temperature setting device.

Claims (1)

[Claims] 1. Based on the detected temperature detected by the hot water outlet temperature detector and the set temperature set by the hot water outlet temperature detector.
In a temperature control device for a gas water heater that performs PID calculation and uses the calculation result to control the fuel gas supply amount to maintain the hot water outlet temperature at a set temperature; And when the integral deviation stored in the register is zero,
A function is added to add or subtract a constant corresponding to the minimum bit digit of the register to the integral term up to the previous time, depending on the presence or absence and sign of a deviation between the detected temperature and the set temperature. Gas water heater temperature control device.