JP3494237B2 - Temperature control device for electrothermal heating element - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature control device,
More specifically, the present invention relates to a temperature control device capable of performing uniform temperature control over the entire temperature range in temperature control used for electric carpets, for example.

[0002]

2. Description of the Related Art A conventional heating tool such as an electric carpet is
It has a structure in which a linear heating element is arranged on the heating surface, and the temperature sensor 1 having the structure shown in FIG. 4 is usually used for temperature detection. That is, the temperature sensor 1 is such that a linear primary conductor 1b is spirally wound around a core thread 1a, a plastic temperature sensitive body 1c such as vinyl chloride is covered thereon, and a linear secondary conductor 1d is wound from the outside thereof. An outer cover 1e made of an insulating material is coated on the outside thereof, and a change in impedance due to the temperature of the plastic temperature sensor 1c is detected by applying a voltage between the primary conductor 1b and the secondary conductor 1d. Is. Incidentally, the voltage to be applied is an AC voltage, the plastic temperature sensitive body 1c is prevented from polarization.

An example of a conventional temperature detecting circuit using the temperature sensor 1 will be described with reference to FIG. In the figure, the temperature sensor 1 and the linear heating element 2 are arranged in a heating element body 3 such as a carpet, and the temperature sensor 1, the heating element 2 and the DC power supply circuit 5 are arranged in parallel with the power source 4. Connected to. In the heat generating circuit, the heat generating element 2 and the switch 6 composed of a relay are connected in series, and the connection with the power source is turned on / off to adjust the amount of heat generated.

In the temperature signal generating circuit 7, resistors 7a, 7b and 7c are connected in series to the primary conductor 1b of the temperature sensor 1 as shown in the figure, and the resistors 7b and 7c and the plastic temperature sensing element 1c form a parallel circuit. As described above, the secondary conductor 1d was connected to one pole of the power source 4 (ground G side). The secondary conductor 1
Both ends of d are short-circuited so that the voltage applied at each position in the longitudinal direction of the plastic temperature sensing element 1c becomes uniform.

The voltage generated between the primary conductor 1b and the secondary conductor 1d is a voltage that depends on the impedance of the plastic temperature sensor 1c, and the voltage generated at the voltage dividing point P of the resistors 7b and 7c is a diode. The set temperature signal V ₀ given to the non-inverting terminal of the comparator 8 as the temperature signal V composed of the DC voltage rectified by 7d and smoothed by the resistor 7e and the capacitor 7f and given from the temperature setting circuit 9
Compared to. In this temperature setting circuit 9, a variable resistor 9a and fixed resistors 9b and 9c are connected in series as shown in the figure, and temperature is set by a slider 9d of the variable resistor 9a.

The comparator circuit is formed by the positive feedback circuit of the comparator 8 including the resistors 8a and 8b, and the temperature signal generating circuit 7
In order to limit the number of times the switch 6 is turned on and off per unit time, the output voltage (temperature signal) V of 1 has an electric hysteresis. When the ON signal is output from the comparison circuit, the switch drive circuit 10 drives the coil 6a to turn on the switch 6, and when the OFF signal is output, the current of the coil 6a is cut off to turn off the switch 6.

By the way, the temperature of the plastic temperature sensing element 1c-
As shown in FIG. 6, the impedance characteristics have such characteristics that a fixed linear relationship is not established, the impedance change per unit temperature change is small at low temperature, and the impedance change becomes large at high temperature. Therefore, as shown in FIG. 7, the temperature difference corresponding to the threshold value ΔV of the comparator 8 is ΔT _L for the low temperature T _L and ΔT for the high temperature T _{H.
If H} and ΔT _M with respect to the intermediate temperature T _M , then ΔT _L > ΔT _M > ΔT _H.

Therefore, when the switch 6 is turned off, the temperature of the heating element body 3 is slowly decreased at a low temperature T _L having a small difference from the room temperature, and the switch 6 is turned on unless it is significantly decreased (temperature difference ΔT _L ). On the other hand, at the high temperature T _H , the temperature of the heating element body 3 rapidly decreases, and the switch 6 turns on due to a small temperature decrease (temperature difference ΔT _H ).

[0009]

In the electric carpet using the conventional temperature control device described above, when the set temperature is set to a low temperature, the carpet turns on and off only about 2 to 3 times per hour, and the carpet becomes cold. There is a problem that the relay (switch) does not turn on easily. Furthermore, since the life of the switch depends on the number of times the contacts are turned on and off, the life of the switch when the set temperature is always set higher than that of the switch when the set temperature is always set low.
There is a problem that the life of the heating element is shortened depending on the use conditions, and the reliability of the heating element product is lowered.

The present invention has been made in view of the above problems. Even when a temperature sensor in which the relationship between the output signal and the actual temperature is not in a linear relationship is used, the control characteristic is maintained in the entire control temperature range. It is an object of the present invention to provide a temperature control device for an electrothermal heating element in which the temperature is uniform.

[0011]

In order to achieve the above object, the temperature control device for an electrothermal heating element according to the present invention is constructed such that an electrothermal heating element includes a heating element switch, a temperature sensor, and a temperature monitoring section. And a switch control unit, the temperature monitoring unit,
When the temperature signal is lower than the set temperature signal, an ON signal is output,
Comparing means for outputting an off signal when it is high, on time measuring means for measuring the output time of the on signal, and off time calculating means, the off time calculating means being preset when the off signal is output. Calculate the off time by subtracting the latest on signal output time from the target on / off cycle
An off time from this off time and at least the previous off time to turning on the switch is calculated, and the switch control unit turns off the switch when the off signal is given,
The switch is turned on when both the ON signal given by the comparison means and the ON signal given by the OFF time calculation means are given.

The switch for turning on / off the electricity supply to the heating element is not particularly limited, but a relay is usually used in an electric carpet or the like having a large current capacity, but a contactless switch may be used. As is clear from the definition, the comparison means is configured to output an on / off signal when the temperature signal and the set temperature signal do not match, and has a hysteresis function like the conventional comparison circuit described in the section of the prior art. It is not configured to have.

The calculation of the off time is not particularly limited, but at least the past switch off time including the previous time,
This can be carried out by obtaining a weighted average value with a time obtained by subtracting the latest ON signal output time from a preset target ON / OFF cycle. The weighted average may be determined with reference to the appropriate situation. For example, the last switch off time,
It is also possible to perform a simple average (that is, weight 1) with the time obtained by subtracting the latest ON signal output time from the target ON / OFF cycle, or to use a moving average for the past OFF time.

Further, the temperature sensor is formed by attaching a pair of electrodes to a plastic temperature sensing element, the temperature setting circuit is formed by a variable resistor, and each of the means of the temperature monitoring unit is executed by a program previously input to a microcomputer. Then, the set temperature signal input to the comparison means is converted into a reference temperature signal corresponding to the impedance of the plastic temperature sensing element in the reference signal generating section.
The temperature signal converted into the number of values can be compared in the comparison unit.

That is, when the temperature monitoring unit is formed by a microcomputer, it is supplied by an ON signal given from the comparison unit and an OFF time calculation unit provided in the microcomputer. Therefore, the detection accuracy of the difference between the temperature signal and the set temperature signal in the comparison unit has a threshold value of the minimum temperature difference obtained by dividing the entire control temperature range into binary numbers.

The subject to which the present invention is applied is not particularly limited, but it can be advantageously applied to a warming tool such as an electric carpet or an electric blanket which normally uses a temperature sensor using a plastic temperature sensitive body. However, the object to which the present invention is applied is not limited to these.

[0017]

When the switch is turned off, the ON signal is output from the comparator, and both the off-time end signals are output from the calculating means, and the means for turning on the switch for the first time depends on whether the set temperature is high or low. It is prevented that the on / off cycle becomes shorter than the target on / off cycle. Further, since the temperature comparison unit has no hysteresis, the on-signal output from the comparator is less likely to be delayed than the off-time end signal from the calculation means, and is prevented from becoming extremely longer than the target on / off cycle. . Therefore, a temperature sensor having a non-linear temperature signal characteristic such as a plastic heat sensitive element is used.
Be used service, or variation control temperature range by controlling the temperature region, OFF cycle is prevented from being varied.

The means according to claim 2, wherein the switch-off time is given by a weighted average of the actual switch-off time and the target on-off period minus the latest switch-on signal output time. It is possible to obtain an effect of approaching the target on / off cycle while making the value more uniform. Further, the temperature sensor is formed of a plastic temperature sensing element, and each means of the temperature monitoring unit is executed by a program previously input to a microcomputer, and a set temperature signal based on a voltage from a variable resistor is applied to the impedance of the plastic temperature sensing element. The means according to claim 3 provided with a reference signal generating section for converting into a reference temperature signal corresponding to, by converting the set temperature signal into a reference temperature signal corresponding to the temperature signal obtained by the plastic temperature sensor, It is possible to make the set temperature change to the set temperature signal given from the outside uniform over the entire temperature range.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the accompanying drawings with reference to the accompanying drawings. The temperature control device for the electrothermal heating element of the present embodiment shown in FIG. 1 has a circuit of a comparator 8 of the temperature control device for the electrothermal heating element according to the conventional example shown in FIG. 5 ) except that the circuit is the same as that shown in FIG. 5 , the same members are designated by the same reference numerals and the description thereof will be omitted.

Next, the flow of each signal will be described with reference to FIG.
It The temperature of the heating element is detected by the temperature sensor 1, and a temperature signal is generated.
Converted to a temperature signal V (voltage) by the raw circuit 7 and binary
After being converted to a modal value signal, it is formed on the computer 11.
Given to the comparison unit 12. Also, the temperature setting circuit 9 can be used.
Temperature setting scale in 1 ° C increments of 25 ° C to 42 ° C on variable resistance 9a
Set temperature signal V₀(Voltage) in binary
Standard converted to a modal value signal and formed in the computer 11
The signal is supplied to the signal generator 13. Computer 11
Each set temperature signal V set by the temperature setting circuit 9₀Corresponding to
Reference signal V _SIs input in advance and the reference signal is generated
In the section 13, the input set temperature signal V₀Corresponding to
Reference signal V_STo read and to give to the comparison unit 12
Operate.

[0021] In comparison portion 12, is compared with the temperature signal V and the reference signal V _S, <OFF signal when is V _S is also V> V is an ON signal at V _S is outputted to the switch control unit 14 It The switch control unit 14 receives the ON signal,
The on-time measuring unit 15 is activated to start counting the on-time. Next, when the OFF signal output from the comparison unit 12 is given to the switch control unit 14, the switch drive circuit is turned OFF and the counting of the ON time is stopped, and the count result is given to the OFF time calculation unit 16 to calculate the OFF time. The unit 16 calculates the off time based on the following arithmetic expression.

[0022]

However, the suffix n is an integer representing the data input order, n = n represents the latest data, and n
= 1 represents the oldest data to be stored. τ is an off time length, and θ is a target on / off cycle, which is set to 240 seconds in this embodiment. χ represents an on-time, a and b (a> b) are integers representing weights, and in this embodiment, n = 2, a = 2,
b = 1 was set.

For example, if the previous off time is 120 seconds and the on time this time continues for 100 seconds, and then the power is switched off, the calculation result of the off operation duration τ performed by the off time calculation unit 16 is τ _n = [120 × (2-1) + (240-100) ×
1] ÷ 2 = 130 (seconds). The switch control unit 14 becomes V> V _S while the off operation is τ _n time (130 seconds in the above example), and the comparison unit
If the ON signal is already output from 12, the ON signal is output to the switch drive circuit 10 at the time when τ _{n has} elapsed, and then the OFF signal is output from the comparison unit 12, the switch drive circuit is output.
An off signal is output to 10, the on time measuring unit 15 is activated again, and the above operation is repeated.

If the comparison unit 12 remains an OFF signal even after the OFF operation duration of the OFF time calculation unit 16 elapses, the switch control unit 14 outputs an OFF signal until the comparison unit 12 turns to an ON signal. Continues, and becomes longer than the target on / off cycle. This action has the effect of ensuring safety in a special case where the heating element body 3 is an electric carpet, for example, when it is affected by another heat source such as kotatsu or is extremely warmed by a futon or the like. Obtainable.

[0026]

As described above, the temperature control device for an electrothermal heating element according to the first aspect of the present invention comprises a comparison means for comparing a temperature signal with a set temperature signal and outputting an on / off signal, and an on time measuring means. Since the on / off of the switch is controlled by the off-time calculating means, the on / off cycle is prevented from changing between high temperature and low temperature, and the variation in the on / off cycle due to the high and low of the set temperature is eliminated, and the switch depending on the usage state. It is possible to eliminate variations in the life of the.

Further, in the temperature control device for the electrothermal heating element according to the second aspect, the time for continuing the switch-off is determined from the actual switch-off time and the time obtained by subtracting the latest on-time from the target on-off cycle. By doing so, the on / off operation of the switch can be matched with the target on / off cycle without difficulty. Further, in the temperature control device for an electrothermal heating element according to claim 3, a plastic temperature sensing element is used as a temperature sensor, a control operation is performed by a microcomputer, and a set temperature signal corresponds to a reference temperature corresponding to the impedance of the plastic temperature sensing element. Since the signal and the temperature signal are compared, the rate of change of the set temperature with respect to the set temperature signal given from the outside can be made linear.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a temperature control device for an electrothermal heating element according to an embodiment of the present invention.

FIG. 2 is an operation explanatory diagram of the control procedure of FIG.

FIG. 3 is a graph showing a control state of the embodiment shown in FIG.

FIG. 4 is a partially cutaway perspective view of a conventional temperature sensor.

FIG. 5 is a temperature control circuit diagram of a conventional electrothermal heating element using the temperature sensor shown in FIG.

6 is a graph showing temperature-impedance characteristics of the temperature sensor shown in FIG.

FIG. 7 is a graph illustrating a control characteristic according to temperature of the control circuit shown in FIG.

8 is a graph illustrating a problem of temperature control operation of the control circuit of FIG.

[Explanation of symbols]

1 Temperature Sensor 2 Heating Element 3 Heating Element Body 6 Switch 7 Temperature Signal Generation Circuit 8 Comparator 9 Temperature Setting Circuit 9a Variable Resistor 10 Switch Drive Circuit 13 Comparison Section 15 Reference Signal Generation Section 17 Switch Control Section 18 On-Time Measurement Section 19 Off Time calculator T Temperature signal T ₀ Set temperature signal

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G05D 23/00-23/32 F24D 13/02 H05B 3/00

Claims (3)

(57) [Claims] 1. An electrothermal heating element, a switch for the heating element,
A temperature sensor, a temperature monitoring unit, and a switch control unit are provided, and the temperature monitoring unit outputs an ON signal when the temperature signal is lower than the set temperature signal, and outputs an OFF signal when the temperature signal is higher than the set temperature signal.
The off-time calculating means comprises an on-time measuring means for measuring the output time of the on-signal and an off-time calculating means. When the off-signal is output, the off-time calculating means outputs the latest on-signal from the preset target on-off cycle. Calculate the off time minus the time, calculate the off time from this off time and at least the previous off time until the switch is turned on,
The switch control unit turns off the switch when the off signal is given, and turns on the switch when both the on signal given by the comparison means and the on signal given by the off time calculation means are given. Type heating element temperature control device. 2. The calculation of the off-time calculating means obtains a weighted average value of past switch-off times including at least the previous time and a time obtained by subtracting the latest on-signal output time from a preset target on-off cycle. Claim 1
A temperature control device for the electrothermal heating element described. 3. A plastic temperature sensing element is used as the temperature sensing element of the temperature sensor, the temperature setting circuit is formed by a variable resistor, and the temperature monitoring is executed by a microcomputer. A reference signal generating section for converting the reference temperature signal corresponding to the temperature signal output from the temperature sensor at a set temperature is formed, and the reference temperature signal is compared with the temperature signal output from the temperature sensor. 1. A temperature control device for an electrothermal heating element according to 1 or 2.