JPS6142165Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a thermostatic oven temperature control circuit, and more particularly to a temperature control circuit used to precisely adjust and maintain the temperature of a crystal oscillator or the like housed inside the thermostatic oven.

In general, temperature control methods for constant temperature chambers can be roughly divided into:
There are continuous control methods and pulse width control methods, and the present invention relates to the latter pulse width control method.

Now, to briefly explain one example of a conventional pulse width control type constant temperature oven temperature control circuit, this circuit is the same as the circuit 9 and switch 11 in FIG. A description will be given of the diagram in which the circuit 9 and switch 11 are removed.

First, inside the constant temperature chamber 1, there is a heater 2 and a temperature-sensitive resistance element 3.
The temperature-sensitive resistance element 3 forms one side of the bridge of the bridge resistance input type voltage comparator 4, and therefore, when a temperature change occurs in the thermostatic chamber 1, the set reference voltage in the voltage comparator 4 and The equilibrium of the bridge that performs the comparison is disrupted, and a corresponding voltage is generated from the voltage comparator 4, and this voltage is input to one input terminal of the second voltage comparator 5. On the other hand, since the voltage obtained by converting the oscillation output voltage from the reference rectangular wave oscillator 8 into a waveform by the waveform converter 10 is input to the other input terminal of the voltage comparator 5, the two inputs are compared, and the voltage From the output side of comparator 5, voltage comparator 4
A periodic pulse having a certain pulse width corresponding to the output voltage from the heater is generated, and this is input to the next stage switching circuit 7, where the heater power supply voltage is switched from the heater power supply power source 6. Heating is controlled and becomes stable once it reaches a constant temperature.

However, in order to shorten the rise time of the temperature in a constant temperature oven, there are cases when trying to obtain a large maximum current by reducing the heater resistance, or when using a heater whose resistance fluctuates widely depending on the temperature. When trying to obtain a large maximum current when the resistance is small, it is necessary to send a large amount of current to the heater current supply circuit, but with the pulse width control method described above, many pulses are connected in series. Since there is a gap between the pulses, in order to increase the effective current value, it is necessary to increase the absolute value of the current. Therefore, a large amount of current flows through the heater current supply circuit, making it difficult to design the temperature control circuit and making the entire thermostatic oven expensive.

Note that when performing temperature control, the desired temperature setting is determined by setting the temperature on one side of the resistance bridge circuit, which has the temperature-sensitive resistance element 3 in the voltage comparator 4, and the other two sides to which the temperature-sensitive resistance element 3 is not connected. This is done by setting the voltage at the series connection point of the resistors to the set reference voltage. When a temperature change occurs in the thermostatic chamber 1, the resistance value of the temperature-sensitive resistance element 3 changes, the balance of the bridge circuit that performs comparison with the set reference voltage is lost, and the voltage comparator 4 detects the temperature-sensitive resistance element 3. A voltage will be generated according to the change in resistance value. This temperature setting method is the same as that of the present invention described later.

The present invention eliminates the above-mentioned drawbacks of the conventional one, and divides the heater heating current waveform into two sections for one period: a period of continuous energization and a period of no energization, and also controls the energization time. It is designed to vary depending on the temperature,
As a result, even when a large effective current is required, the absolute value of the current can be made relatively small, thus facilitating the design of the heater current supply circuit and reducing the cost of the entire thermostatic oven. .

Furthermore, another object of the present invention is to efficiently use the maximum capacity of the power supply for heating the heater to its limit. The ratio of the time when the heating current is continuously energized and the time when it is not energized for one cycle of the heating current,
That is, the duty conversion rate is set to be large or small, respectively.

The present invention will be explained below by way of examples with reference to the drawings.

FIG. 1 shows a block circuit diagram of the entire embodiment of the present invention. In the present invention, the circuits newly provided compared to the conventional one are a duty conversion circuit shown at 9 in FIG. 1 and a duty setting switch shown at 11 for controlling the duty conversion circuit. A detailed circuit diagram of this newly provided part is shown in FIG.

When explaining FIG. 1, the explanation of the circuit layout will be omitted since it is completely the same as the explanation of the conventional circuit except for the duty conversion circuit 9 and the duty setting switch 11, and the following will refer to the whole of FIG. The operation shown in FIG. 1 based on this will be explained.

Figure 2 shows the duty conversion circuit 9 in Figure 1.
2 is a specific detailed circuit diagram of the duty setting switch 11 and the duty setting switch 11. FIG. In FIG. 2, SW indicates a duty setting switch corresponding to 11 above, 1C ₁ to 1C ₄ are exclusive OR circuits, 1C ₅ is a NOR circuit, and 1C ₁ to 1C ₄ and 1C ₅ are gate circuits. 1C ₆ is a flip-flop,
1C ₇ indicates a hexadecimal counter, and 1C ₈ indicates an inverter.

Next, to explain the operation in Figure 2, the exclusive
One input terminal of each of the OR circuits _1C1 to _1C4 is fixed to the level H or L set by the switch SW (in Fig. 2, only the input terminal of the exclusive OR circuit _1C3 is H). , each other input terminal is connected to the Q output of counter _1C7 . At this time, the input is added to CK of counter _1C7 , and the Q output of counter _1C7 is Q _A = Q _B = Q _D =
Only when L, Q _C = H (4 in decimal notation), all outputs of exclusive OR circuits 1C ₁ to 1C ₄ become L.
The output of NOR circuit _1C5 is then H
This becomes the input clock signal for the flip-flop _1C6 . In flipflop 1C ₆ ,
The H level of the D input is transmitted to the Q output by this clock signal.

Furthermore, an input is added to counter 1C ₇ , and the C _O output of counter 1C ₇ is Q output Q _A = Q _B = Q _C =
It becomes L only when Q _D =H, and the inverter
It is inverted by IC8, becomes H, and is applied as a clear signal to the CL input of flip-flop _1C6 . When the CL input of flip-flop _1C6 becomes H, the Q output changes to L. In other words, the Q output of the flip-flop _1C6 is the Q output of the counter _{1C7 .}
= Q _B = Q _D = L, Q _C = H (4 in decimal notation) to Q _A = Q _B = Q _C = Q _D = H (15 in decimal notation) It is held at H.

FIG. 3 shows a time chart of the input signal and output signal of the counter _1C7 , and shows the time chart for the state described above. In FIG. 3, if the input signal duty is 50%, the output signal duty is 68.75%. That is, (N-1)-M/N=(16-1)-4/16=68.75
% Here, M: Number of switch SW settings N: Maximum count number of counter _1C7 , duty can be converted by switch SW.

Next, turning to a description of the overall operation of FIG. 1, the rectangular wave output of the reference oscillator 8 is applied to the duty converter 9, where it becomes the duty pulse output determined by the duty setting switch 11 as described above. This pulse signal is applied to the waveform converter 10 to become a triangular wave, and is applied to the B terminal of the voltage comparator 5. As shown in FIG. 4, the waveform converter 10 is an integrating circuit consisting of a capacitor C and a resistor R, and converts a rectangular wave signal, which is an input signal to the waveform converter, into a triangular wave signal. This situation is shown in FIGS. 8 to 10. Among them, a indicates an input rectangular wave, and b indicates an output triangular wave. Figure 8 shows the case of the conventional system where the duty conversion rate of the input wave is fixed at 50%, and Figures 9 and 10 show the cases where the duty conversion rate of the input wave of the present invention is 25% and 75%, respectively. ing. On the other hand, a voltage change based on a change in the resistance value of the temperature-sensitive resistance element 3 is applied to a bridge resistor input type voltage comparator 4, compared with the reference voltage in the voltage comparator 4, and becomes the output of the voltage comparator 4. This is the A terminal input. Voltage comparator 5 compares the DC voltage of A and B
A pulse voltage is generated by comparing the triangular wave voltages and is applied to the switching circuit 7. This pulse signal turns on and off the switching circuit 7, thereby turning on and off the output of the heater power supply power source 6, and supplies the power to the heater 2. In this way, temperature changes in the thermostatic chamber 1 are sensed and compensated for, thereby accurately maintaining the temperature at a constant temperature. Also the second
By increasing the number of duty setting switches 11 shown in the figure and the number of electrical system elements corresponding thereto, the number of desired adjustment temperatures can be increased by that amount.

In the present invention, by adding the duty conversion circuit 9 and the switch 11, it is possible to change the duty of the rectangular wave signal that is the input signal to the waveform converter 10. Therefore, it is possible to change the width of the triangular wave signal that is the output signal of the waveform converter 10.

Therefore, comparison of input and output signals of the voltage comparator 5 will be explained using FIGS. 5, 6, and 7. FIG. 5 is a diagram explaining the conventional method, and FIGS. 6 and 7 are diagrams explaining the method of the present invention. 5, 6 and 7, a is a triangular wave signal which is the B input signal of the voltage comparator 5, b is the A input signal and B input signal of the voltage comparator 5, and c is the voltage comparator 5 input signal. Shows the output signal.

Here, b in each figure indicates that when the temperature of the thermostatic chamber is low and the A input signal is small, that is, when the power is turned on,
Or voltage comparator 5 when heater resistance 2 is small, etc.
The A input signal and the B input signal are shown.

Now, in the conventional system shown in FIG. 5, since the width of the triangular wave signal is constant, the pulse width of FIG. 5c, which is the output signal of the voltage comparator 5, is constant.

On the other hand, in the method of the present invention shown in FIGS. 6 and 7, the width of the triangular wave signal can be changed using the duty setting switch 11, the duty conversion circuit 9, and the waveform converter 10. As shown in FIG. 6c and FIG. 7c, it becomes possible to change the pulse width of the output signal of the voltage converter 5.

From the above, when the capacity of the power supply is small, the pulse width is set by the switch 11 and the duty conversion circuit 9 so that the triangular wave signal shown in FIG. 6a is obtained, and when the capacity of the power supply is large, Figure 7a
By setting the triangular wave signal shown in
It is possible to efficiently supply the maximum capacity of the power supply to the heater 2.

As explained above, in accordance with the present invention, by adding a duty setting switch and a duty conversion circuit to the conventional circuit, even when it is desired to flow a large current to the heater of a thermostatic oven, the current capacity of the supply power source 6 can be maximized. Since it is possible to use up to a certain value, current can be efficiently supplied to the heater 2, and therefore the heater power source, switching circuit, and thermostatic oven can be made smaller, lower in price, and improved in reliability.

[Brief explanation of the drawing]

Fig. 1 is a block circuit diagram of an embodiment of the present invention;
The figure shows a detailed circuit diagram of the duty conversion circuit 9 and duty setting switch 11 in Figure 1, and
The figure shows a time chart for explaining the operation of FIG. Figure 4 is a circuit diagram of the waveform converter in Figure 1,
FIG. 5 is an input/output waveform diagram of the voltage converter 5 according to the conventional method, and FIGS. 6 and 7 are input/output waveform diagrams of the voltage converter 5 according to the method of the present invention.
In the figure, a and b are the input waveform diagrams, and c is the output waveform diagram. FIG. 8 is an input/output waveform diagram of the waveform converter 10 according to the conventional method, and FIGS. 9 and 10 are input/output waveform diagrams of the waveform converter 10 according to the present invention. is its input waveform diagram, and b is its output waveform diagram. The symbols used in the drawings indicate the following. 1... Constant temperature chamber, 2... Heater, 3... Temperature sensitive resistance element, 4... Bridge resistance input type voltage comparator, 5
...Voltage comparator, 6...Heater power supply current, 7
... Switching circuit, 8 ... Reference square wave oscillator, 9 ... Duty conversion circuit, 10 ... Waveform converter, 11 ... Duty setting switch (SW), 1C ₁ to 1C ₄ ... Exclusive OR circuit, 1C _Five …
...NOR circuit, 1C6...Flip-flop, 1
C ₇ ... Hexadecimal counter, 1C ₈ ... Inverter.

Claims (1)

[Scope of utility model registration request] A bridge resistor input type voltage comparator whose one side is a temperature-sensitive resistance element in a constant temperature oven, and a fluctuating voltage from this voltage comparator as one input, and the oscillation output voltage from a reference square wave oscillator is converted into a waveform by a waveform converter. a second voltage comparator having the converted voltage as its other input;
In the pulse width controlled constant temperature oven temperature control circuit comprising a switching circuit that switches the constant temperature oven heater heating power according to the output voltage from the second voltage comparator, the reference rectangular wave oscillator and the waveform converter are provided. and a gate circuit that includes a duty setting switch for temperature control, a counter, and a gate circuit that generates a clock signal at any desired period using the switch and the counter, and a clock signal from the gate circuit and a clock signal from the counter. 1. A constant temperature chamber temperature control circuit comprising a duty converter comprising a flip-flop that outputs a periodic pulse of a desired pulse width in response to a clear signal.