JPH0570164B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a device for determining the cause of deviation, and more specifically, a temperature detection thermistor whose one end is connected to a power supply via a resistor and a temperature setting variable resistor whose one end is grounded are connected in series. and a plurality of resistors that divide the power supply at a predetermined ratio to output a reference voltage, and a connection point between the resistor and thermistor connected to the power supply, and a connection point between the plurality of resistors. , whether voltage fluctuations in the detected voltage obtained from the connection point between the resistor and thermistor of the bridge circuit configured to output a voltage corresponding to the deviation between the set temperature and the detected temperature are caused by temperature changes; The present invention relates to a deviation cause determination device that determines whether the deviation is due to a change in set temperature.

Conventionally, the bridge circuit described above has been employed as a water temperature detection means for proportionally controlling the amount of fuel supplied in gas water heaters, etc., as shown in FIG. 6, for example. Since the thermistor as a temperature detection means and the variable resistor as a temperature setting means are connected in series, fluctuations in the detected voltage obtained from the connection point between the resistor and thermistor are not due to fluctuations in the detected temperature. It was not possible to determine whether this was caused by a change in the set temperature or by a change in the set temperature.

Hereinafter, the configuration of the conventional example shown in FIG. 6 will be briefly described.

In other words, in proportional control, overshoot of hot water temperature is likely to occur when the load fluctuates, especially when the flow rate decreases. The detection voltage is determined by comparing the overshoot determination voltage Vc′, which is set at a predetermined temperature higher than ′.
An overshoot discrimination circuit 4' is provided which detects the occurrence of overshoot due to load fluctuation when Va' is higher than the discrimination voltage Vc', and when the occurrence of overshoot is detected, the proportional control circuit 1′
The system was configured to temporarily stop the operation of the engine and reduce the amount of fuel supplied.

Therefore, when operating the variable resistor VR' as a temperature setting means to decrease the resistance value in order to lower the set temperature, the input signal to the overshoot discrimination circuit 4', that is, the detected voltage from the thermistor RT' Since Va' causes the same change as when the water temperature rises, the overshoot discrimination circuit 4'
malfunctions and reduces the amount of fuel supplied.
As a result, there was a drawback that undershoot occurred before the water temperature reached a predetermined temperature, causing the water temperature to fluctuate significantly.

Note that 2' is a proportional valve whose opening degree is adjusted by a drive circuit 3' controlled by the output V' of the proportional control circuit 1'.

The present invention has been made in view of the above circumstances, and its purpose is to determine whether the cause of variation in the detection voltage for temperature detection is due to a change in hot water temperature or a change in set temperature. It is an object of the present invention to provide a deviation cause determination device equipped with means for reliably determining the cause of deviation.

In order to achieve the above object, the deviation cause determination device according to the present invention differentiates the voltage between the thermistor and the variable resistor to obtain a differential value, and compares the differential value with a set reference value. , is characterized in that it is provided with differential value determining means for determining the cause of variation in the detected voltage.

The above configuration will be explained below based on the block diagram shown in FIG.

A resistor R1, a thermistor RT as a temperature detection means, a bias correction resistor RS, and a variable resistor as a temperature setting means are connected between the ground point of the power supply Vcc.
Resistors R2 and R3 connect VR in series and divide the power supply Vcc to generate a reference voltage Vb.
A temperature detection bridge circuit S configured by
an integrator AI that generates an output V corresponding to the deviation Δt between the reference voltage Vb and the detected voltage Va corresponding to the detected temperature t obtained from the connection point A of the thermistor RT and the resistor R1 connected to the thermistor RT; A combustion control device configured by a PID control circuit 1 equipped with a PID control circuit 1 and a proportional valve drive circuit 3 that determines the opening degree of a proportional valve 2 that adjusts the fuel supply amount based on the output V of the control circuit 1, The cause of the fluctuation in the detection voltage Va is a change in the resistance of the thermistor RT due to temperature fluctuation, or a change in the variable resistor due to a change in the set temperature.
It is determined whether it is a resistance change in VR, and if it is a temperature change, that is, an overshoot has occurred due to a flow rate change, etc., the operation of the PID control circuit 1 is temporarily stopped and the combustion supply amount is changed. In order to perform control to reduce the
is provided.

The overshoot limiter 4 includes a temperature deviation determination circuit that detects the occurrence of overshoot by checking the deviation Δt of the detection voltage Va with respect to the reference voltage Vb obtained from the connection point B of the resistors R2 and R3. 5. Differential value determining means 6 for determining the cause of variation in the detected voltage Va based on the voltage between the thermistor RT and the variable resistor VR, that is, the voltage at the connection point C in FIG. 1, and the temperature deviation Each output E of the discrimination circuit 5 and the differential value discrimination means 6,
An AND circuit 7 for calculating the logical product of F is provided.

For example, if the thermistor RT is a type whose resistance value decreases as the temperature rises, the thermistor
When the ambient temperature of RT increases, the detection voltage Va at the connection point A between resistor R1 and thermistor RT decreases, and the voltage between thermistor RT and variable resistor VR increases.

On the other hand, when the variable resistor VR is operated to decrease the resistance value, that is, to decrease the set temperature in order to change the temperature setting, the detection voltage Va at the connection point A between the resistor R1 and thermistor RT decreases, and the voltage between the thermistor RT and the variable resistor decreases.
The voltage between it and VR also drops.

In other words, when the ambient temperature around thermistor RT increases and when the variable resistor VR is operated to decrease the resistance value, that is, to decrease the set temperature to change the temperature setting, the connection point A between resistor R1 and thermistor RT The detection voltage Va falls in both cases and is indistinguishable, but the detection voltage Va of the thermistor RT and variable resistor VR
The voltage between them increases in the former case and decreases in the latter case.

The differential value determining means 6 differentiates the voltage between the thermistor RT and the variable resistor VR to obtain a differential value, and compares the differential value with a set reference value α2. Detect the direction of change in voltage between resistor R1 and thermistor RT, and determine whether the cause of variation in detected voltage Va at connection point A between resistor R1 and thermistor RT is due to temperature change or change in set temperature. It is to determine whether

The determination result of the differential value determining means 6 is that in the configuration shown in FIG. 1, when the voltage drop at the connection point A is observed,
Only when it causes a change in temperature can it be used to activate the overshoot limiter and reduce the fuel supply.

Even if the thermistor RT is of a type whose resistance value increases as the temperature rises, the detection voltage Va at the connection point A between resistor R1 and thermistor RT and the thermistor
The relationship in the direction of change of the voltage between RT and the variable resistor VR is the same as above, and the cause of the variation in the detected voltage Va can be determined in the same manner as above.

Therefore, as described above, it has been possible to provide a deviation cause discriminating device that can discriminate whether the cause of variation in the detection voltage for temperature detection is due to a temperature change or a change in the set temperature.

Hereinafter, specific embodiments of the present invention will be described based on the drawings.

As shown in Figure 2, the power supply
The thermistor RT connected to Vcc and the temperature setting variable resistor VR whose one end is grounded are connected to the correction resistor Rs.
and three resistors R
2, R3, and R4 to divide the power supply Vcc into a predetermined ratio, and apply reference voltages Vb, Vd from each connection point B, D.
A temperature detection bridge circuit S configured to output a detected temperature t output from a connection point A between the reference voltage Vb, the resistor R1, and the thermistor RT.
A PID control circuit 1 that calculates the output V corresponding to the deviation Δt from the detected voltage Va corresponding to A valve drive circuit 3 is provided to constitute a combustion control device that proportionally controls the hot water temperature of the gas water heater.

The PID control circuit 1 includes a buffer circuit A0 that receives the detection voltage Va of the bridge circuit S and outputs it to the differentiator A1, an integrator A2 that integrates the output of the differentiator A1, and an output of this integrator A2. By comparing V and a lower limit value VL corresponding to the minimum opening degree of the proportional valve 2, that is, the minimum fuel supply amount by dividing the voltage of the power source into a predetermined ratio, the output V is determined to be this lower limit value.
An operational amplifier A3 is provided as a saturation prevention means for regulating the active range of the integrator A2 so that it does not fall below VL.

Furthermore, as mentioned above, in order to prevent transient responses such as overshoot from occurring in the control response due to sudden changes in the amount of hot water dispensed, an overshoot limiter 4 is provided which is equipped with a deviation cause determination device configured as described below.
is provided.

The overshoot limiter 4 is configured by an overshoot discrimination voltage Vd generated from a connection point D between the detection voltage Va and the resistors R3 and R4.
A comparator A4, which generates an output E of "H" level when the detected temperature t exceeds a reference temperature t0' which is set a predetermined value higher than the set temperature t0, and the thermistor RT. Two operational amplifiers A5 and A6 that calculate the differential value ΔG with respect to the detection voltage Vc from the connection point C with the variable resistor VR, a differentiator 8 consisting of a capacitor, etc., and the output ΔG of the differentiator 8 and the power supply. The detected voltage is compared with the reference voltage α2, which is the set reference value from the resistors R5 and R6, which divides and outputs Vcc at a predetermined ratio.
“H” when the rate of change ΔG of Vc is greater than the predetermined value α2 and the direction corresponds to the temperature rise
A comparator A7 generates a level output F, and an AND circuit 7 composed of diodes D1, D2, transistors Q1, Q2, etc., which calculates the AND of the outputs E and F. Therefore,
The differentiator 8 and the comparator A7 function as the differential value determining means 6.

The overshoot limiter 4 configured as described above is configured such that the deviation of the detected voltage Va from the thermistor RT is equal to or greater than a predetermined value α1 due to a flow rate change, and the rate of change ΔG thereof is a predetermined value α2. Only when the above is detected, a predetermined voltage corresponding to the resistor R7 is added to the input of the integrator A2 of the PID control circuit 1 using the output G of the AND circuit 7, and the fuel supply amount is adjusted to the Control is performed to temporarily reduce the amount to the lower limit amount VL.

Therefore, even if the variable resistor VR is operated to change the set temperature t0, the overshoot limiter 4 will not operate because the direction of voltage fluctuation at the connection point C is opposite to the temperature fluctuation. First, control circuit 1
will not malfunction.

Incidentally, Fig. 3 is a time chart showing the operation of the combustion control device explained above, and Fig. 3A shows the response of the hot water temperature t when the set temperature is lowered by operating the variable resistor VR. , Figure B shows the response of hot water temperature when the amount of hot water output changes.

Furthermore, the response indicated by the broken line in the figure shows the response when the deviation cause determination device according to the present invention is not provided, as in the conventional example.

Another embodiment will be described below with reference to the drawings.

As shown in FIG. 4, this embodiment is a combustion control device having basically the same configuration as the embodiment shown in FIG. It is configured to apply a predetermined voltage to the input of the differentiator A1 to control the amount of fuel supplied.

That is, since the polarities of the input signals of the differentiator A1 and the integrator A2 are inverted, the transistor Q2 is used to invert the output polarity of the AND circuit 7.
is omitted, and the polarity of the diode D3 inserted between the output G and the differentiator A1 is inverted.

Further, as shown in FIG. 5, the buffer circuit A
A resistor RG that determines the gain of 0 is configured in the flow sensor so that its resistance value changes in accordance with the flow rate, so that the gain of the PID control circuit 1 is automatically adjusted in response to the change in flow rate. It may be configured as follows.

Alternatively, the differentiator A1 may be omitted from the PID control circuit 1 to form a normal proportional control circuit.

Furthermore, the entire combustion control device except for the proportional valve 2 may be configured by a microcomputer,
Various changes are possible.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the configuration of the present invention, Figure 2 is a block diagram showing the configuration of the present invention.
The figure is a circuit diagram of a combustion control device showing a specific configuration of the present invention, FIGS. 3A and 3B are time charts showing its operation, FIGS. 4 and 5 are circuit diagrams showing another embodiment, and FIG. 6 is a block diagram showing the configuration of a conventional example. R1, R2, R3...Resistor, Vcc...Power supply,
RT...Thermistor, VR...Variable resistor, Va...
...Detection voltage, Vb, Vc...Reference voltage, A, B, C
. . . Connection point, 6 . . . Differential value determination means.

Claims (1)

[Claims] 1 A temperature detection thermistor RT whose one end is connected to the power supply Vcc via a resistor R1 and a temperature setting variable resistor VR whose one end is grounded are connected in series, and the power supply Vcc is divided at a predetermined ratio. It has a plurality of resistors R2 and R3 that output a reference voltage Vb, and a connection point A between the resistor R1 and thermistor RT connected to the power supply Vcc, and the plurality of resistors R
2, the resistor R1 and thermistor RT of the bridge circuit S configured to output a voltage corresponding to the deviation between the set temperature and the detected temperature from the connection point B of R3.
A deviation cause determining device for determining whether a voltage fluctuation of a detected voltage Va obtained from a connection point A between the thermistor RT and the variable temperature is caused by a temperature change or a change in the set temperature. Differentiate the voltage between the resistor VR and find the differential value, compare the differential value with the set reference value α2,
A deviation cause discriminating device comprising a differential value discriminating means 6 for discriminating the cause of variation in the detected voltage Va.