WO2008018654A1

WO2008018654A1 - Magnetic field-free temperature controller and temperature control method using dual timing signals

Info

Publication number: WO2008018654A1
Application number: PCT/KR2006/004632
Authority: WO
Inventors: Jong-Jin Kil
Original assignee: Jong-Jin Kil
Priority date: 2006-08-08
Filing date: 2006-11-07
Publication date: 2008-02-14
Also published as: KR100886662B1; KR20080013685A

Abstract

Disclosed herein is a magnetic field-free temperature controller and temperature control method using dual timing signals. The temperature controller includes a heating cable and a control unit. The heating cable includes first and second heating wires concentrically arranged and a Negative Temperature Coefficient thermistor wound between the first and second heating wires. The second heating wire is made of a material having a positive characteristic. The control unit is configured to detect overheating, a open circuit, or a short circuit, which exists between the first and second heating wires, using a first timing signal, and detect the overheating of the second heating wire itself using a second timing signal. Therefore, heating power can be controlled and temperature can be reduced without using a separate temperature sensor.

Description

MAGNETIC FIELD-FREE TEMPERATURE CONTROLLER AND TEMPERATURE CONTROL METHOD USING DUAL

TIMING SIGNALS

Technical Field

[1] The present invention relates, in general, to a magnetic field-free temperature controller and temperature control method for a heating cable for bedding, which are capable of detecting heating and a shortcircuit in a magnetic field-free manner and without short-circuiting one end of the heating cable used in a heating apparatus, such as an electric floors, an electric mat or an electric heating pad and, more particularly, to a temperature controller and a temperature control method, which, when first and second heating wires, which are concentrically arranged inside and outside a Negative Temperature Coefficient (NTC) plastic nylon thermistor (or NTC thermistor), overheat, detect dual temperatures from the heating cable using a NTC characteristic, in which the resistance of a NTC plastic nylon thermistor decreases, and a Positive Temperature Coefficient (PTC) characteristic, in which the internal electrical resistance of the heating cable itself increases, thus being capable of controlling heating power and thus decreasingtemperature without a separate temperature sensor.

[2]

Background Art

[3] Generally, heating apparatuses for electrically heated bedding, such as electric floors, electric mats and electric heating pads, are provided with heating cables therein, so that heat can be generated when power is supplied to the heating cables.Accordingly, a temperature controller for detecting the temperature around the heating cable or controlling the supply of power according to a user's selection is essentially provided in the heating apparatuses.

[4] In a conventional heating cable for bedding, one end of each of two metallic heating wires is short-circuited, and temperature is detected by a separate temperature sensor spaced apart from the heating cable. However, in the method in which the temperature sensor is spaced apart from the heating cable, there are problems in that the temperature, which is generated when the internal circuit of the heating cable is short- circuited, cannot be detected throughout the heating cable, and also in that local overheating at an arbitrary location cannot be detected. Accordingly, if the heating cable overheats locally, is short-circuited, or is open-circuited, fire and electric shocks may occur.

[5] Another conventional method includes a method of adding a separate tempera- turesensor around the outer circumference of or in the central portion of two metal- licheating wires which are concentrically arranged, one end of each of which forms a short circuit, and detecting temperature using a third wire. However, the method of detecting temperature using the third wire, which is not spaced apart from the heating cable, is problematic in that a temperature sensor layer and a third metal layer are added to the heating cable, and thus it cannot be used for thin bedding due to the increase in the thickness of the magnetic field-free heating cable, the process of manufacturing the heating cable is complicated, and the manufacturing cost thereof is increased.

[6] Furthermore, the conventional technologies described above must be provided with respective separate temperature sensors, so that they have disadvantages in that the practicality of use is decreased by the increase in the thickness of each of the heating cables and in that the temperature control efficiency of each of the heating cables is not good.

[7] Meanwhile, although an improved method of controlling temperature using an NTC thermistor without using a temperature sensor has been disclosed by thepresent applicant, the reliability of overheating prevention must be increased through additional overheating detection and control, other than primary overheating detection and control using an NTC plastic nylon thermistor, and the temperature must be more rapidly and precisely controlled.

[8]

Disclosure of Invention Technical Problem

[9] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide atemperature controller and a temperature control method, which primarily detect overheating using a NTC plastic nylon thermistor, and secondarily detect overheating using a PTC plastic nylon thermistor, thus rapidly and reliably preventing overheating.

[10] Another object of the present invention is to provide a temperature controller and a temperature control method, which generate primary and secondary timing signals for temperature detection, determine whether the overheating of a heating cable is occurring using the timing signals, and control the flow of heating current according to the states of detected signals.

[11] A further object of the present invention is to provide a temperature controller and a temperature control method, which uses a half wave of alternating current (AC) power for temperature detection, and the other half wave thereof for heating and, at the same time, detects a PTC temperature at the zero point of the AC power to avoid in- terference due to the AC power. [12]

Technical Solution

[13] In order to accomplish the above objects, the present invention provides a magnetic field-free temperature controller using dual timing signals, including a heating cable comprising first and second heating wires, which are concentrically arranged and connected such that current input into eitherof the first and second heating wires is output via a remaining heating wire in a reverse direction, and a NTC thermistor, which is wound between the first and second heating wires, the second heating wire being made of a material having a positive characteristic in which the internal electrical resistance of the material increases as temperature increased and a control unit configured to detect overheating, a open circuit, or a short circuit, which exists between the first and second heating wires, using a first timing signal, and thus primarily detect a first temperature based on the state of a first detection signal, to detect the overheating of the second heating wire itself using a second timing signal,and thus secondarily detect a second temperature based on the state of a second detection signal, and to output a heating signal if no abnormality occurs at a time of detection of the first and second temperatures; wherein the current flowing through any of the first and second heating wires flows out through a remaining heating wire, so that the directions of currents flowing through the first and second heating wires are opposite each other and magnetic fields induced by the currents are cancelled, therefore no magnetic field is formed.

[14] The magnetic field-free temperature controller further includes a first temperature signal voltage supply unit connected to one side of the heating cable and configured to supply a first signal voltage; a first temperature signal detection unit connected between the first and second heating wires at the remaining side of the heating cable and configured to detect the first signal voltage supplied from the first temperature signal voltage supply unit; a second temperature signal voltage supply unit configured to supply a second signal voltage to one end of the second heating wire; and a second temperature signal voltage detection unit connected in parallel with the second temperature signal voltage supply unitand both ends of the second heating wire, and configured to detect the second signal voltage supplied from the second temperature signal voltage supply unit; wherein the control unit directs the supply of heating current when the first temperature signal detection unit detects a voltage at a level equal to or higher than a predetermined level and the second temperature signal voltage detection unit detects a voltage at a level lower than the predetermined level, which is applied to both ends of the second heating wires. [15] The control unit does not directs the supply of the heating current when the first temperature signal detection unit detects a voltage at a level lower than the predetermined level.

[16] The control unit does not direct the supply of the heating current when the second temperature signal voltage detection unit detects a voltage at a level equal to or greater than the predetermined level, which is applied across both ends of the second heating wire.

[17] The first signal voltage supplied from the first temperature signal voltage supply unit is input into either of the first and second heating wires, is supplied in a reverse direction and is then detected by the first temperature signal detection unit, when the temperature of the NTC thermistor is lower than a predetermined temperature, and is completely or partially supplied via the NTC thermistor in the reverse direction, when the temperature of the NTC thermistor is equal to or greater than the predetermined temperature.

[18] The second temperature signal voltage detection unit detects the value of a voltage across both ends of the second heating wire at the time of application of the second signal voltage supplied from the second temperature signal voltage supply unit, and t ransfers the detected voltage value to the control unit.

[19] The second temperature signal voltage detection unit directly proportionally amplifies a signal voltage at both ends of the second heating wire and transfers the amplified voltage value to the control unit when the signal voltage at both ends of the second heating wire is low.

[20] The first signal voltage is periodically supplied from the first temperature signal voltage supply unit at every half cycle of input AC power.

[21] The second signal voltage is periodically supplied from the second temperature signal voltage supply unit using a separate input power source.

[22] The second signal voltage is applied at the zero-phase time point of AC current supplied from the power source to the heating cable.

[23] The second temperature signal voltage detection unit includes an amplification element for amplifying the detected second temperature signal; anda setting volume for setting a reference voltage to be compared with the amplified second temperature signal.

[24] The second temperature signal voltage detection unit includes reverse voltage control rectification elements, and protects the second temperature signal voltage supply unit and the second temperature signal voltage detection unit from the heating voltage applied to the first and second heating wires protects.

[25] In addition, the present invention provides a magnetic field-free temperature control method using dual timing signals in a temperature controller, the temperature controller including a heating cable that comprises first and second heating wires, which are concentrically arranged and connected such that current input into either of the first and second heating wires is output to a remaining heating wire in a reverse direction, and an NTC thermistor, which is wound between the first and second heating wires, the heating of the second heating wire being interrupted when the heating cable having a PTC characteristic, in which internal electrical resistance increases as temperature increases, is heated to a high temperature higher than a specific level at the time of increase in temperature, the method comprising; a first signal voltage generation step of a first temperature signal voltage supply unit generating a first signal voltage, that is, a temperature detection half cycle voltage, in each half cycle of an AC power for temperature detection a first signal voltage detection step of a first temperature signal detection unit, which is connected to one end of the heating cable, detecting the first signal voltage that is output from the first temperature signal voltage supply unit and passes through any of the first and second heating wires; a timing signal generation step of generating a timing signal for generating a second temperature signal voltage using the program of a control unit; a second signal voltage generation step of a second temperature signal voltage supply unit generating a second voltage signal at regular intervals in response to the timing signal for generating the second temperature signal voltage, and supplying the generated second voltage signal to the second heating wire; a second signal voltage detection step of a second temperature signal voltage detection unit, which allows the second temperature signal voltage supply unit and both ends of the second heating wire to be connected in parallel, detecting a voltage across both ends of the heating wire; and a heating control step of supplying heating current to the heating cable only when a voltage at a level equal to or higher than a predetermined level is detected at the first signal voltagedet ection step and a voltage at a level lower than the predetermined level is detected at the second signal voltage detection step, and interrupting the heating current when a voltage at a level lower than the predetermined level is detected at the first signal volt- agedetection step or when a voltage at a level equal to or higher than the predetermined level is detected at the second signal voltagedetection step.

[26] After a voltage at a levellower than the predetermined level is detected at the first signal voltage detection step or when a voltage at a level equal to or higher than the predetermined level is detected at the second signal voltage detection step, the heating current is supplied again when a voltage at a level equal to or higher than the predetermined level is detected at the first signal voltage detection step and a voltage at a levellower than the predetermined level is detected at the second signal voltage detection step

[27] The second signal voltage is periodically supplied from the second temperature signal voltage supply unit using a separate power source.

[28] The second signal voltage is applied at the zero-phase time point of AC current supplied from the power source to the heating cable. Advantageous Effects

[29] The present invention primarily detects overheating using the NTC thermistor and secondarily detects overheating using the heating cable, taking advantage of the PTC positive characteristic of the NTC thermistor and the heating cable, so that it can more rapidly and sensitively detect the overheating of the heating cable.

[30] The present invention allows the temperature controller to generate first and second timing signals without using a separate temperature sensor, can determine whether overheating occurs according to the temperature detection voltages, whichare detected from the heating cable, using these timing signals, and can control theflow of heating current according to the result of the determination.

[31] The present invention candetect temperature using DC current supplied at regular intervals while using a half wave of the AC power for temperature detection and the other half wave of the AC power for heating, and not only can detect overheating but also control temperature by applying temperature signal voltages at the time point at which mutual interference occurs.

[32]

Brief Description of the Drawings

[33] The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: [34] FlG. 1 is a circuit diagram showing the state in whicha temperature controller and a heating cable are connected to each other according to a present invention; [35] FlG. 2 isa circuit diagram showing, in detail, the circuit diagram of FlG. 1 ;

[36] FlG. 3 isa circuit diagram in which protection circuits are added to the circuit diagram of FlG. 2; [37] FlG. 4 is a circuit diagram in which an amplificationcircuit is added to the circuit diagram of FlG. 3;

[38] FlG. 5 is a diagram illustrating the detection of first and second temperatures;

[39] FlG. 6 is a diagram illustrating a heating operation and a heating stop operation based on the operation method of the present invention;

[40] FlG. 7is an equivalent circuit illustrating the detection of the first temperature; and

[41] FlG. 8 is an equivalent circuit illustrating the detection of the second temperature.

[42]

Best Mode for Carrying Out the Invention [43] The constructions of the present invention are described in detail with reference to embodiments shown in the accompanying drawings.

[44] FlG. 1 is a circuit diagram showing the state in which a temperature controller and a heating cable are connected to each other according to a present invention. With reference to FlG. 1, an NTC plastic nylon thermistor (generally referred to as an NTC thermistor) 13 is wound between a first heating wire 11 and a second heating wire 12, and an insulation cover 14 is wound outside the second heating wire 12. At the time of overheating, the impedance of the NTC plastic nylon thermistor 13 is lowered, so that current flows between the first and second heating wires 11 and 12 in a re- versedirection, therefore voltage is lost.

[45] On the power source side of the heating cable 1, the first heating wire 11 is connected to a first temperature signal voltage supply unit 100 and a trigger input unit 200, and the second heating wire 12 is connected to the power source. On the other side of the heating cable 1, the first heating wire 11 and the second heating wire 12 are connected to a first temperature signal detection unit 300.

[46] The first temperature signal voltage supply unit 100 functions to supply a signal voltage to the first heating wire 11 at every half cycle of input AC power. The signal voltage, which is supplied from the first temperature signal voltage supply unit 100 at regular intervals, passes through the heating cable 1 along the first heating wire 11, is provided to the opposite side of the heating cable 1, and is detected by the first temperature signal detection unit 300 and, at the same time, is supplied to the second heating wire 12 in the reverse direction.

[47] The NTC plastic nylon thermistor 13 is a device the resistance of which decreases as temperature increases in temperature. A portion of a first temperature signal, which is supplied from the first temperature signal voltage supply unit 100 and passes through the first heating wire 11, flows to the second heating wire 12 via the NTC plastic nylon thermistor 13 because the resistance value of the NTC plastic nylon thermistor 13 is lowered when temperature increases between the first heating wire 11 and the second heating wire 12. In this case, the signal voltage detected by the second temperature signal voltage detection unit 300 is lower than the signal voltage supplied from the first temperature signal voltage supply unit 100. In this case, when the signal voltage detected by the first temperature signal detection unit 300is lower than a preset reference voltage, whether overheating occurs is determined and the supply of heating current is interrupted.

[48] That is, the fact that the signal voltage supplied from the first temperature signal voltage supply unit lOOis not detected by the first temperature signal detection unit 300 or is detected at a low voltage means that the heating cable 1 has overheated, and thus the internal impedance of the NTC thermistor is lowered and the signal voltage is not supplied through the NTC thermistor in the reversedirection, therefore the signal voltage does not reach the first temperature signal detection unit 300, or is attenuated and transferred. In this case, the control unit 700 does not supply the heating current until the signal voltage is detected by the first temperature signal detection unit 300, that is, until the temperature of the heating cable 1 decreases, without intentionally interrupting power.

[49] Even when the first temperature signal voltage supply unit 100 is short-circuited, no signal voltage is received from the first temperature signal detection unit 300, and thus the control unit 700 can detect the state of the first temperature signal voltage supply unit 100 based on the reception state of the signal voltage. When no signal voltage is received from the first temperature signal detection unit 300, the control unit 700 determines that the first heating wire 11 or second heating wire 12 of the heating cable 1 has been short-circuited, or that the first temperature signal voltage supply unit 100 has been short-circuited, and then interrupts the supply of the heating current.

[50] The second temperature signal voltage supply unit 400 supplies a signal voltage to the second heating wire 12. The second heating wire 12 (the first heating wire may also be used according to a user's selection) is made of a material having a positive (+) electrical resistance temperature coefficient, that is, a material having a PTC, so that a phenomenon in which resistance increases as temperature increases can be used. The second temperature signal voltage detection unit 500 is connected with both ends of the second heating wire 12, and detects the signal voltage applied to both ends of the second heating wire 12. That is, voltage supplied from the second signal voltage supply unit 400 is applied to both ends of the second heating wire 12 and is dropped across the second heating wire 12. Thereafter, the voltage across both ends of the second heating wire 12is measured.

[51] The second heating wire 12 is made of a material having a positive (+) electrical resistance temperature coefficient, and the electrical resistance value thereof varies according to the temperature coefficient in the case where the heating cable 1 overheats, and thus the second temperature signal voltage across the second heating wire 12 is dropped in direct proportion to the electrical resistance value, thereforethe voltage across both ends of the second heating wire 12 can be measured by the second temperature signal voltage detection unit 500. In this case, when the voltage across both ends of the second heating wire 12, which is measured by the second temperature signal voltage detection unit 500, is higher than a reference voltage, the control unit 700determines that overheating has occurred and then interrupts the supply of the heating current.

[52] The control rectifier 24 is connected in parallel with the first temperature signal voltage supply unit 100, and is turned on in response to the trigger signal of the trigger input unit 200. It is preferred that a power control Silicon-Controlled Rectifier (SCR) be used as the control rectifier 24. When turned on in response to the trigger signal, the reversing rectifier 15 causes the heating current to flow in the reverse direction.

[53] The timing input unit 600 supplies an AC power timing signal to the control unit

700. The control unit 700 reads the timing cycle of the AC power input from the timing input unit 600, reads the temperature signal voltages detected by the first temperature signal detection unit 300 and the second temperature signal voltage detection unit 500 in the preceding half cycle of the AC power, and determines whether to perform heating in the next half cycle thereof based on the read information.

[54] The control unit 700 reads the first temperature signal voltage in the interval of FlG.

5 (c), which belongs to the preceding half temperature detection cycle of the AC power (FlG. 5 (a)), and performs both the supply and detection of the second temperature signal voltage in the AC power zero phase point period of FlG. 5 (b). The control unit 700 transfers a timing signal to the second temperature signal voltage supply unit 400 in the zero point period, and reads the temperature signal voltage detected by the second temperature signal voltage detection unit 500 in a timing signal period. The control unit 700 reads two types of signals, that is, the first and second temperature signal voltages, in each half cycle of the AC power, and determines whether to perform heating in the heating interval of FlG. 5 (a).

[55] Whether to perform heating is determined by the control unit 700 while the first temperature signal voltage, which is detected by the first temperature signal detection unit 300, and the second temperature signal voltage, which is detected by the second temperature signal voltage detection unit 500, are compared with a reference voltage potential set through the control input and output unit 800 through the adjustment of a temperature control volume. In this case, if the result of the comparison falls within an appropriate range, a heating temperature is not reached, so that the control unit 700 turns on the control rectifier 24. When the control rectifier 24 is turned on, the first heating wire 11 and the second heating wire 12 are heated.

[56] The control unit 700 supplies the heating current only when the first signal voltage, which is detected by the first temperature signal detection unit 300, is equal to or higher than the reference voltage, and the second signalvoltage across both ends of the second heating wire 12, which is detected by the second temperature signal voltage detection unit 500, is lower than the reference voltage. Heating is stopped in the case where either of the two conditions is not satisfied, and is performed again only when both of the two conditions are satisfied. That is, in the case where the first temperature signal voltage is not detected,like the oblique line portion of FlG. 6 (d), or in the case where the second temperature signal voltage higher than the reference voltage is detected, like the oblique line portion of FlG. 6 (e), the heating is stopped.

[57] When the first temperature signal voltageis not detected, or when the second temperature signal voltage is higher than the reference voltage by the adjustment of the temperature control volume of the control input and output unit 800, the heating temperature of the heating cable is sufficiently high. Accordingly, the control unit 700 directs the stop of heating and the control input and output unit 800 interrupts the trigger signal used for the control rectifier 24, therefore the control rectifier 24is turned off.

[58] The control input and output unit 800 is a part constructed such that the user can set various types of manipulation and the temperature control volume as well as the input and output of the control unit 700. The power source unit 900 is a part constructed to supply power to the control unit 700 or supply power necessary to allow the second temperature signal voltage supply unit 400to supply the second temperature signal voltage.

[59] The undescribed reference numerals 51 and 52 indicate elements for protecting circuitry by preventing the high heating temperature of the second temperature signal voltage detection unit 500 and the first temperature signal voltage from interfering with the second temperature signal voltage supply unit 400 and the second temperature signal voltage detection unit 500. Diodes may be used as these elements. The reference numeral 51 indicates a diode for lowering the voltage potential to 0 V so that a high reverse voltageis not applied to the second temperature signal voltage supply unit 400 and the second temperature signal voltage detection unit 500, and the reference numeral 52 indicates a diode for preventing a high reverse voltage from being applied to the second temperature signal voltage supply unit 400 and the second temperature signal voltage detection unit 500.

[60] FlG. 2is a circuit diagram showing, in detail, the circuit diagram of FlG. 1. With reference to FlG. 2, the first temperature signal voltage supply unit 100 includes a resistor 10. When the trigger input unit 200 compares the signal voltage, which is detected at the time of the supply of the timing signal, with the reference voltage, and performs detection normally, the control rectifier 24 is turned on in response to the trigger signal and allows the heating current to flow from one end of the first heating wire 11, which is connected to the power source, to the second heating wire 12 in the reverse direction. The trigger input unit 200 is connected with the control rectifier 24, and the reversing rectifier 15 is connected between the first heating wire 11 and the second heating wire 12.

[61] The trigger input unit 200 includes resistors 21 and 22, and a photo coupler 23. In the first temperature signal detection unit 300, a zener diode 31, a resistor 32, and a photo coupler 33 are connected in series. [62] The second temperature signal voltage supply unit 400 includes a photo coupler 42 and a resistor 41, which are connected in series. The second temperature signal voltage detection unit 500 includes a resistor 53. The timing input unit 600includes a resistor 61. The control input and output unit 800 includes a volume control resistor 81, resistors 82, 85 and 86, and photo couplers 83, 84 and 87. The power source unit 900 includes a resistor 91, a diode 92, a zener diode 95, and condensers 93 and 94.

[63] The first temperature signal voltage supplied from the first temperature signal voltage supply unit 100 is detected by the first temperature signal detection unit 300, and the second temperature signal voltage supplied from the second temperature signal voltage supply unit 400 is detected by the second temperature signal voltage detection unit 500 using direct current (DC) power supplied from the power source unit 900.

[64] FlG. 3 is a circuit diagram in which protection circuits are added to the circuit diagram of FlG. 2. With reference to FlG. 3, a construction for protecting the circuitry of FlG. 2is additionally provided. A unidirectional rectifier 19and a positive voltage zener varistor 20, which are indicated by reference character A, are connected in series to each other. The zener varistor 20 has a bidirectional characteristic and the rectifier 19 has a unidirectional characteristic. For this reason, in the case where the control rectifier 24 is short-circuited, the temperature signal voltage for the detection of temperature is applied unchanged, so that excessive current flows at a voltage higher than the rated voltage, therefore the rectifier 19 and the zener varistor 20 function to perform an operation of cutting the fuse when the current is bypassed. When the control rectifier 24 is short-circuited, excessive bidirectional current flows and the fuse is cut by the excess current, so that the circuitry can be prevented from overheating.

[65] Reference character B is used in the case where the shield is wound outside the heating cable 1, and functions to allow the control unit 700to interrupt power when a short circuit is formed between the shield 16 and the second heating wire 12 due to the overheating of the heating wires 11 and 12, and voltage is thus detected by the resistors 17 and 18.

[66] FlG. 4 is a circuit diagram in which an amplification circuit is added to the circuit diagram of FlG. 3. With reference to FlG. 4, circuitry units indicated by reference numerals 500A and 500B include Operational Amplifiers (OP Amps) 57 and 59, respectively, and function to amplify respective input signals when the voltage of the second temperature signal voltage detection unit 500 is low. In particular, the OP Amp 57 is used to amplify the signal of the second heating wire 12 when the signal level of the second heating wire 12 is low.

[67] Reference numeral 500A indicates a temperature setting comparison circuit.

Reference numeral 58 in the temperature setting comparison circuit indicates a temperature setting volume. Reference numerals 55 and 56 in the circuit unit 500B are semi-fixed volumes, and are used to adjust amplification levels. The amplified temperature signal voltage is compared with a reference voltage set by the temperature setting volume 58, and whether to perform heating is determined by the control unit 700 based on the result of the comparison.

[68] FlG. 5 is a diagram illustrating the detection of first and second temperatures. With reference to FlG. 5, a half wave of the input AC power is used for heating, and the other half wave thereof is used for temperature detection. The first temperature signal voltage for the detection of a first temperature is supplied via the first temperature signal detection unit 100 in each half temperature detection cycle of the AC power. In this case, the supplied temperature signal voltage is periodically supplied to have the width of FlG. 5 (c).

[69] Meanwhile, the second temperature signal voltage is detected at the same cycle as that of (b) of FlG. 5 at the time of the generation of a timing signal. The second temperature signal voltage is detected at the temperature detection half wave start zero point of the AC input power of (a) of FlG. 5, that is, at a zero point at which there is no interference due to AC power voltage, while the second temperature signal voltage is supplied.

[70] FlG. 6 is a diagram illustrating a heating operation and a heating stop operation based on the operation method of the present invention. With reference to FlG. 6, FlG. 6 (a) shows an AC power waveform, FlG. 6 (b) shows the AC timing signal in the control unit, FlG. 6 (c) shows the supply of the second temperature signal voltage, FlG. 6 (d) shows the detection of the first temperature signal voltage, FlG. 6 (e) shows the detection of the second temperature signal voltage, FlG. 6 (f) shows the SCR tri gger signal, and FlG. 6 (g) indicates heating wires heating current.

[71] In FlG. 6 (d), the SCR trigger signal shown in FlG. 6 (f) is also not generated in an interval in which the first temperature signal voltage is not detected, therefore the heating operation is not performed.

[72] In FlG. 6 (e), the SCR trigger signal shown in FlG. 6 (f) is not generated in an interval in which the second temperature signal voltage is detected, therefore the heating operation is not performed.

[73] Accordingly, it can be seen that thefirst temperature signal voltage is detected according to the supply of the first and second temperature signal voltage,and the heating wires are heated only when the second temperature signal voltage is low.

[74] FlG. 7is an equivalent circuit illustrating the detection of the first temperature. With reference to FlG. 7, temperature detection current passes through the second heating wire 12, is detected by the photo coupler 87, and then flows out to the first heating wire 11. In this case, when the temperature of the NTC plastic nylon thermistor 13 increases, a portion i-1 of the current flows out to the NTC plastic nylon thermistor. Accordingly, the photo coupler 87detects a voltage lower than a normal voltage. In the case where the first temperature signal voltage is lower than the reference voltage when the first temperature signal voltage is compared with the reference voltage, heating current does not flow.

[75] FlG. 8is an equivalent circuit illustrating the detection of the second temperature.

With reference to FlG. 8, the second temperature signal voltage is detected at both ends of the second heating wire 12. In this case, the photo coupler 84 supplies DC signal voltage at thezero point of the AC power. In this case, the resistance value increases due to the increase in the temperature of the second heating wire 12, so that the voltage across a series resistor 41 decreases in proportion to the applied voltage, therefore the voltage across the two ends of the second heating wire 12 can be measured.

[76] The present invention primarily detects the first temperature signal voltage in order to detect overheating using the NTC plastic nylon thermistor disposed between the two heating wires, and secondarily detects the second temperature signal voltage in order to detect overheating via the PTC second heating wire, that is, dually detects overheating, and thus can provide a safer and more reliable overheating prevention temperature controller and temperature control method.

[77]

Industrial Applicability

[78] The present invention primarily detects overheating using the NTC thermistor and secondarily detects overheating using the heating cable, taking advantage of the PTC positive characteristic of the NTC thermistor and the heating cable, so that it can more rapidly and sensitively detect the overheating of the heating cable.

[79] The present invention allows the temperature controller to generate first and second timing signals without using a separate temperature sensor, can determine whether overheating occurs according to the temperature detection voltages, whichare detected from the heating cable, using these timing signals, and can control theflow of heating current according to the result of the determination.

[80] The present invention can detect temperature using DC current supplied at regular intervals while using a half wave of the AC power for temperature detection and the other half wave of the AC power for heating, and not only can detect overheating but also control temperature by applying temperature signal voltages at the time point at which mutual interference occurs.

[81] Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. [82] [83]

Claims

[1] A magnetic field-free temperature controller using dual timing signals, comprising: a heating cable comprising first and second heating wires, which are concentrically arranged and connected such that current input into either of the first and second heating wires is output via a remaining heating wire in a reverse direction, and a Negative Temperature Coefficient (NTC) thermistor, which is wound between the first and second heating wires, the second heating wire being made of a material having a positive characteristic in which internal electrical resistance of the material increases as temperature increased and a control unit configured to detect overheating, a open circuit, or a short circuit, which exists between the first and second heating wires, using a first timing signal, and thus primarily detect a first temperature based on a state of a first detection signal, to detect overheating of the second heating wireitself using a second timing signal, and thus secondarily detect a second temperature based on a state of a second detection signal, and to output a heating signal if no abnormality occurs at a time of detection of the first and second temperatures; wherein the current flowing through any of the first and second heating wires flows out through a remaining heating wire, so that directions of currents flowing through the first and second heating wires are opposite each other and magnetic fields induced by the currents are cancelled, therefore no magnetic field is formed.

[2] The magnetic field-free temperature controller according to claim 1, further comprising: a first temperature signal voltage supply unit connected to one side of the heating cable and configured to supply a first signal voltage; a first temperature signal detection unit connected between the first and second heating wires at a remaining side of the heating cable and configured to detect t he first signal voltage supplied from the first temperature signal voltage supply unit a second temperature signal voltage supply unit configured to supply a second signal voltage to one end of the second heating wire and a second temperature signal voltage detection unit connected in parallel with the second temperature signal voltage supply unit and both ends of the second heating wire, and configured to detect the second signal voltage supplied from the second temperature signal voltage supply unit wherein the control unit directs supply of heating current when the first temperature signal detection unit detects a voltage at a level equal to or higher than a predetermined level and the second temperature signal voltage detection unit detects a voltage at a level lower than the predetermined level, which is applied to both ends of the second heating wires.

[3] The magnetic field-free temperature controller according to claim 2, wherein the control unit does not directs supply of the heating current when the first temperature signal detection unit detects a voltage at a level lower than the predetermined level.

[4] The magnetic field-free temperature controller according to claim 2, wherein the control unit does not direct supply ofthe heating current when the second temperature signal voltage detection unit detects a voltage at a level equal to or greater than the predetermined level, which is applied across both ends of the second heating wire.

[5] The magnetic field-free temperature controller according to claim 2, wherein the first signal voltage supplied from the first temperature signal voltage supply unit is input into either of the first and second heating wires, is supplied in a reverse direction and is then detected by the first temperature signal detection unit, when a temperature of the NTC thermistor is lower than a predetermined temperature, and is completely or partially supplied via the NTC thermistor in the reverse direction, when the temperature of the NTC thermistor is equal to or greaterthan the predetermined temperature.

[6] The magnetic field-free temperature controller according to claim 2, wherein the second temperature signal voltage detection unit detects a value of a voltage across both ends of the second heating wire at a time of application of the second signal voltage supplied from the second temperature signal voltage supply unit, and transfers the detected voltage value to the control unit.

[7] The magnetic field-free temperature controller according to claim 6, wherein the second temperature signal voltage detection unit directly proportionally amplifies a signal voltage at both ends of the second heating wire and transfers the amplified voltage value to the control unit when the signal voltage at both ends of the second heating wire is low.

[8] The magnetic field-free temperature controller according to claim 2, wherein the first signal voltage is periodically supplied from the first temperature signal voltage supply unit at every half cycle of input alternating current (AC) power.

[9] The magnetic field-free temperature controller according to claim 2, wherein the second signal voltage is periodically supplied from the second temperature signal voltage supply unit using a separate input power source.

[10] The magnetic field-free temperature controller according to claim 9, wherein the second signal voltage is applied at a zero-phase time point of AC current supplied from the power source to the heating cable.

[11] The magnetic field-free temperature controller according to claim 2, wherein the second temperature signal voltage detection unit comprises: an amplification element for amplifying the detected second temperature signal; and a setting volume for setting a reference voltage to be compared with the amplified second temperature signal.

[12] The magnetic field-free temperature controller according to claim 2, wherein the second temperature signal voltage detection unit comprises reverse voltage control rectification elements, and protects the second temperature signal voltage supply unit and the second temperature signal voltage detection unit from the heating voltage applied to the first and second heating wires protects.

[13] A magnetic field-free temperature control method using dual timing signals in a temperature controller, the temperature controller including a heating cable that comprises first and second heating wires, which are concentrically arrangedand connected such that current input into either of the first and second heating wires is output to a remaining heating wire in a reverse direction, and an NTC thermistor, which is wound between the first and second heating wires, heating of the second heating wirebeing interrupted when the heating cable having a Positive Temperature Coefficient (PTC) characteristic, in which internal electrical resistance increases as temperature increases, is heated to a high temperature higher than a specific level at a time of increase in temperature, the method comprising; a first signal voltage generation step of a first temperature signal voltage supply unit generating a first signal voltage, that is, a temperature detection half cycle voltage, in each half cycle of an AC power for temperature detection a first signal voltage detection step of a first temperature signal detection unit, which is connected to one end of the heating cable, detecting the first signal voltage that is output from the first temperature signal voltage supply unitand passes through any of the first and second heating wires; a timing signal generation step of generating a timing signal for generating a second temperature signal voltage using a program of a control unit a second signal voltage generation step of a second temperature signal voltage supply unit generating a second voltage signal at regular intervalsin response to the timing signal for generating the second temperature signal voltage, and supplying the generated second voltage signal to the second heating wire a second signal voltage detection step of a second temperature signal voltage detection unit, which allows the second temperature signal voltage supply unit and both ends of the second heating wire to be connected in parallel, detecting a voltage across both ends of the heating wire and a heating control step of supplying heating current to the heating cable only when a voltage at a level equal to or higher than a predetermined level is detected at the first signal voltage detection step and a voltage at a level lower than the predetermined level is detected at the second signal voltage detection step, and interrupting the heating current when a voltage at a level lower than the predetermined level is detected at the first signal voltage detection step or when a voltage at a level equal to or higher than the predetermined level is detected at the second signal voltage detection step.

[14] The method according to claim 13, wherein, after a voltage at a level lower than the predetermined level is detected at the first signal voltage detection step or when a voltage at a level equal to or higher than the predetermined level is detected at the second signal voltage detection step, the heating current is supplied again when a voltage at a level equal to or higher than the predetermined level is detected at the first signal voltage detection step and a voltage at a level lower than the predetermined level is detected at the second signal voltage detection step

[15] The method according to claim 13, wherein the second signal voltage is periodically supplied from the second temperature signal voltage supply unit using a separate power source.

[16] The method according to claim 15, wherein the secondsignal voltage is applied at a zero-phase time point of AC current supplied from the power source to the heating cable.