JPS58145084A - Temperature control system for heater - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Concerning body temperature control methods.

Conventionally, in order to automatically control the temperature of electric heating appliances, etc., it was common to use a thermostat that turns on and off electric current depending on the temperature to maintain the desired temperature.

Thermostats that use bimetals and those that use temperature sensors and semiconductor circuits are common.

In these conventional methods, the temperature of the heat generating resistor (hereinafter referred to as the heating element) rises, which causes the temperature of the heated object to rise, and the temperature of the thermostat there to rise.
Control was started when the temperature rose to an appropriate level.

In other words, the thermostat operated with a certain time delay from the temperature rise of the heating element. This method was suitable for devices with slow temperature rises. However, if you want to rapidly raise the temperature of the heating element, this delay will make it impossible to control the heating element, which will increase the temperature over the heating element's life and destroy the heating element, so this method is not suitable for use. there were.

However, it is human nature to desire equipment that warms up immediately when the switch is turned on, such as heating elements used in space heaters, electrical openers, or office equipment, and this has made possible the emergence of electric heating appliances that heat quickly. requires a temperature control method with much faster response performance than traditional thermostats. Although there is a method of using a temperature sensor such as a radiation thermometer with good response performance, this is very expensive and is not suitable as a sensor at low temperatures.

The present invention was invented in response to such demands, and an object of the present invention is to provide a means for reliably and inexpensively performing temperature control with a quick response from a relatively low temperature to a high temperature.

The details will be explained below.

To control the temperature of a heating element, you must first know its temperature. Conventionally, a temperature sensor such as a thermistor or a bimetal was used for this purpose, but the present invention is characterized by using the heating element itself as a temperature sensor.

A heating element that generates heat by electric power, whether it is a metal resistor or a semiconductor resistor, generally changes its resistance value depending on temperature changes.

The manner in which it changes is determined by the material and shape of the resistor, and can be known in advance.

Therefore, if the resistance value of the heating element is measured at that point in time, the temperature of the heating element at that time can be detected from the data checked in advance and the resistance value.

Various types of resistors such as pure metals, alloys, and semiconductors have been put into practical use as resistors used as heating elements. This inner wire metal has a relatively large positive temperature coefficient and good linearity between temperature and resistance. Alloys have smaller temperature coefficients than pure metals. Some metal vapor deposited films have negative temperature coefficients. Semiconductor resistors include POSISTOR (trade name), which has a positive temperature coefficient, and thermistor, which has a negative temperature coefficient, and the temperature coefficient itself is generally larger than that of metals.

Some examples of resistance changes in heating elements are shown in Figure 1'f.

In FIG. 1, A shows the resistance change due to temperature of pure metal, B and C show the resistance change of alloy, and D and E show the resistance change of semiconductor.

As shown in A, the linearity of the temperature change and resistance change is good over a wide range of resistance changes due to pure metals. In the case of alloys, as shown in B and C, the rate of change is smaller than that of pure metals, and linearity may collapse above a certain temperature. For example, Chromel A (Ni77%, Cr2O%, Fθ, 1y3
% alloy), the temperature coefficient of resistance sometimes changes from positive to negative between about 6oO and 800°C.

D shows the change in resistance of a POSISTOR with a positive temperature coefficient, and 1E shows a thermistor with a negative temperature coefficient.

A heating element like Contour C has a region where two temperatures correspond to one resistance value. In such regions, special consideration is required when temperature control is performed using resistance values.

In this way, various types of resistors have been put into practical use, ranging from resistors for high-temperature furnaces to low-temperature resistors (tens to hundreds of displacements) for far-infrared radiation, but in each case, the relationship between temperature and resistance is important. There is a certain relationship between them, and it is generally possible to calculate the temperature from the resistance value.

Once the temperature is detected, it is easy to control the current of the heating element using known control techniques.

FIG. 2 is a block diagram showing one embodiment of the present invention.

In Figure 2, 1 is a heating element, 2 is a current detector, 3 is a voltage detector, 4 is a clock device, 5 is a sampling circuit, 6 is a calculation circuit, 7 is a temperature setting device, 8 is a comparator, and 9 is a processing device. 10 is a swing circuit, and 11 is a power supply.

How the temperature control of the present invention is performed will be explained with reference to FIG.

Electric power is supplied to the heating element l from a power source 11. At this time, the voltage applied to the heating element l and the current flowing through it are determined by the voltage detector 6.
is detected by the current detector 2.

The detected value is periodically sampled by a clock device 4 and a sampling circuit 5, and the value is sent to a calculation circuit 6. The calculation circuit 6 divides the voltage value by the current value to calculate the resistance value, calculates the temperature information value from the temperature-resistance value data checked in advance, and sends the result to the comparator 8. A value corresponding to the temperature information value of the heating element l according to a desired temperature is set in the temperature setting device 7, and the value is sent to the comparator 8.

The comparator 8 compares the numerical value representing the temperature of the heating element 1 supplied from the calculation circuit 6 with the value from the temperature setting device, and determines whether the temperature information value of the heating element 1 is above the set value. A comparison is made to see if they are below or exactly the same, and the signal is sent to the processing circuit 9.

In accordance with the signal from the comparison circuit 8, the processing circuit 9 sends to the switching circuit 1o a signal that determines the energization time rate.

The switching circuit 10 repeatedly opens and closes in response to a signal from the processing circuit 9, and controls the current to an amount corresponding to the energization time rate.

A specific example of the control will be described with reference to FIG. 6 in the case of an AC power source, in which a thyristor is used in the switching circuit IO and control is performed by adjusting the firing angle.

FIG. 3 is a diagram showing the voltage and current waveforms at each stage of temperature control, where F is the voltage waveform applied to the heating element l, and G is the current waveform.

Figure 3 shows that when the heating element 1 reaches the set temperature T°C, the current is limited to almost zero, and when the temperature of the heating element 1 drops to T-37°C, the full load current is reduced again. flowing temperature i
This is an example of a so-called on-off control system in which the temperature is raised to T°C.

An alternating current voltage is applied to the heating element 1 as shown in FIG. 6F. Then, at an appropriate time just before the voltage becomes zero at the end of each half cycle, the clock device 4 and the sampling circuit 5 sample the voltage value and current value at that time. FIG. 3 ts shows the timing of this sampling. These values are sent to calculation circuit 6. The current is passed in all phases in each half cycle until the temperature of the heating element 1 reaches the set temperature. This is to raise the temperature as quickly as possible.

FIG. 6 01, G2 is an example of this.

When it becomes clear from the signal from the comparator 8 that the temperature IW calculated from the sample values of voltage and current has reached the set temperature,
The processing circuit 9 delays the switching circuit 100 firing angle;
Firing at time ts. As mentioned above, the time ts is set close to the end of each half stroke, so even if it is ignited here, only a small amount of current will flow. When several cycles in which almost no current flows in this way continue, the temperature of the heating element decreases to T-37°C because the supplied energy is small. The waveforms of the current during this period are as shown at 05, G4, and G5 in FIG. 6G. When it is determined from the signal from the comparator 8 that the temperature has decreased to T-37 DEG C. in this way, the processing circuit 9I''i switching circuit 10 is instructed to conduct electricity in all phases again.

This state is 06 and G7 in FIG. 3G. Then, when the temperature rises again and reaches T℃, the firing angle is delayed again for a time t.
8 and allow the temperature to drop from T'C. The waveform of the current at this time is shown in FIG. 608.

In this way, the temperature of the heating element 1 is controlled between T°C and T-37°C.

A remarkable feature of this method is that since the heating element 1 itself is used as a temperature sensor, there is no time delay unlike normal thermostat control. In conventional thermostat control, the temperature of the heated object continues to rise for a while even after the thermostat turns off the current, but with this method, the temperature begins to drop as soon as the current is cut off.

In FIG. 3, the voltage and current values at time t8 may be calculated every cycle, and the values may of course be calculated every cycle or every few cycles.

In either case, in order to sample the resistance value, it is necessary to keep the current value that starts flowing from ts sufficiently small. This is because if the temperature of the heating element 1 continues to rise due to the current for sampling, it will become uncontrollable.

Also, Fig. 3 shows a type of control similar to on/off control, but after the temperature reaches T'C, there are other methods of controlling T±Δ'I''CK temperature other than on/off control, such as proportional control. Needless to say, the known automatic control technology can be applied.

Although Fig. 6 shows the case of an AC power source, the control can be performed in the same way with a DC power source.

FIG. 4 is an embodiment of the on/off control of the DC power supply according to the present invention.

In Fig. 4, H is the voltage of the DC power supply applied to the heating element 1, and K
is also a current, not shown, but is a well-known switching circuit (e.g. an iris chopper) controlled by a signal from the clock device 4. is standing up.

Sampling is performed at a time ts immediately before each cutting point To. The distance between TO and T1 is kept extremely short.

When it is determined through sampling that the temperature has reached T°C, the control is turned off, and when the temperature reaches T-ΔT°C, it is turned on, as in the case of the AC power supply shown in FIG. Fourth
In the figure, 1, K2, and K5 are the current waveforms when they are on, and 3 and K4 are the current waveforms when they are off.

The clock device 4, calculator 6, comparator 8, and processing circuit 9 described above can be easily realized using ordinary microcomputer elements. In this case, voltage and current are detected and converted into digital values by 7dA-D conversion, and then processed.

Although known current detectors 2 and voltage detectors 3 are used, digital ones are easier to use when combined with a microcomputer element.

Although the phase of the switching circuit 10 is generally controlled using a power thyristor, simple on/off control may be performed using a mechanical switch or a solid state relay. In this case, the resistance of the heating element 1 is measured using an ordinary resistance meter while the power is turned off. At this time, current and voltage detectors 2 and 3 are not required. However, care must be taken so that the resistance meter does not break when the power supply 11 is on.

The temperature setting device 7 can be realized by a variable resistor and a variable voltage or current generator in full combination with a standard voltage source such as a Chener diode when the value from the calculation circuit 6 is an analog value. When the value from the calculation circuit 6 is a digital value, it can be realized by a digital value generator using a digital switch or the like.

In the above description, the resistance of the heating element 1 is measured by sampling, but sampling is not necessarily required, and it goes without saying that measurement and monitoring may be carried out at all times.

When constantly detecting resistance values, always apply a high frequency power source to the heating element 1 so as not to interfere with the current value from the power source 11, and install appropriate filters on the power source 11 side, the high frequency power source side, and the resistance measurement circuit side. Insert it to measure resistance using high-frequency current. In this way, the resistance of the heating element 1 can be detected at all times regardless of whether the power source 11 is on or off.

In the case of an AC power supply, the phase of the AC and the sampling period must be synchronized, but this is done by detecting all the times when the AC voltage becomes zero, reading out a certain time from that time with the clock device 4, and setting the sampling period. It can be easily achieved by making a decision.

As mentioned above, the resistance value of the heating element itself is detected, the temperature of the heating element is calculated from the relationship between the temperature of the heating element and the resistance value, which has been checked in advance, and the current value to the heating element is calculated based on that information. The present invention, which controls the temperature of the heating element by controlling the temperature of the heating element, provides the following many features and effects.

(1) Since it is possible to control without delay even a fast heating type heating element whose temperature rises rapidly, it is possible to realize a fast heating type heating element that does not cause an excessive rise in temperature.

(2) There is no need to provide a separate temperature sensor.

(3) Since there is no delay in measuring the temperature of the heating element, the range of temperature fluctuation of the heating element relative to the set temperature can be reduced.

(4) Since high-speed response temperature sensing can be performed without using an expensive temperature sensor such as a radiation thermometer, an inexpensive control device can be obtained.

(5) Since the average temperature of the heating element is detected instead of the local temperature, the average amount of heat generated can be reliably controlled.

(6) Since the temperature sensor is not brought into contact with the heating element, the temperature of the heating element will not locally change entirely due to the influence of the temperature sensor, and a heating element with a uniform temperature can be obtained.

(7) Since the heating element itself is a temperature sensor, unlike conventional thermostats, there is no danger of the life of the temperature sensor.

As described above, according to the present invention, high-speed response temperature control with many features is possible, and its economical effects are significant.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the resistance change depending on the temperature of the heating element, FIG. 2 is a block diagram showing an embodiment of the present invention, and FIGS.
The figure is a diagram showing voltage and current waveforms at each stage of temperature control. DESCRIPTION OF SYMBOLS 1... Heating element, 2... Current detector, 3... Voltage detector, 4... Clock device, 5.' Sampling circuit,
6... Calculation circuit, 7... Temperature setting device, 8... Comparator, 9... Processing circuit, 10 Switching circuit, 11
·power supply. -15- Figure 1 Figure 2 LL History - [k

Claims (1)

[Claims] Detects the resistance value of a heating element that generates heat by supplying current, calculates temperature information of the heating element from the relationship between the temperature of the heating element and the resistance value, and compares this temperature information with preset temperature information. 1. A temperature control method for a heating element, characterized in that the entire current supplied to the heating element is controlled.