JP2005083989A - Input circuit of thermocouple - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an input circuit of a thermocouple exerting no influence on a temperature detection value of a thermo-electromotive force (direct-current voltage) by using an alternative-current signal, having a simple constitution, a rough design and excellent convenience, and capable of detecting a disconnection. <P>SOLUTION: This circuit is equipped with a temperature sensor comprising a thermocouple 2 and a compensating lead wire 3, and a disconnection detection means 4 having a signal generation means 7, an amplification means 8 and a disconnection determination means 9. When detecting the temperature of an object, a thermo-electromotive force (direct-current voltage) VT value acquired by converting the temperature can be detected accurately, and when the thermocouple 2 or the compensating lead wire 3 is disconnected, the disconnection can be surely determined from the state (VO→VH) wherein the alternative-current signal is changed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a thermocouple input circuit that detects the temperature of an object by forming a temperature sensor by connecting a thermocouple and a compensating lead wire, and in particular, affects the DC detection value of temperature using an AC signal. The present invention relates to a thermocouple input circuit for detecting disconnection of a thermocouple or a compensating lead wire.

  In the conventional thermocouple input circuit, when a DC voltage is applied via a resistor, a minute DC current is passed through the thermocouple and the compensating conductor, and the disconnection occurs in the thermocouple or the compensating conductor, the applied DC voltage is Disconnection is detected based on the changed state.

  FIG. 7 shows a block diagram of an embodiment of a conventional thermocouple input circuit. In FIG. 7, a thermocouple input circuit 50 includes a temperature sensor by connecting one end of a thermocouple 51 and a compensating lead wire 52 at connection points A and B, and connecting the other end of the compensation lead wire 53 to connection points B1 and B2. To the amplifier 53. Further, the reference DC power supply Vrf is connected to the connection point B1 through the resistor R.

  The compensating lead wire 52 is formed of two kinds of lead wires, ie, a compensating lead wire L1 and a compensating lead wire L2, which are formed of an alloy material which is the same as or close to the two kinds of alloys constituting the thermocouple 51, and changes depending on the alloy material and the length X. A compensating lead wire resistance r.

  The temperature sensor composed of the thermocouple 51 and the compensating conductor 52 generates a thermoelectromotive force (DC voltage) according to the temperature of the object between the connection terminals B1 and B2. Between the connection terminals B1 and B2, the reference DC power supply Vrf → resistor R → connection terminal B1 → compensation lead L1 → connection terminal A1 → thermocouple 51 → connection terminal A2 → compensation lead L2 → connection terminal B2 → ground ( A minute current IS of the order of μA (microampere) for detecting disconnection of the temperature sensor is passed through the current path of GND). Due to this minute current IS, a voltage drop of a resistance obtained by adding the compensation lead wire resistance r of the compensation lead wire L1, the resistance of the thermocouple 51, and the compensation lead wire resistance r of the compensation lead wire L2 to the connection terminals B1 and B2.

  When the temperature sensors of the thermocouple 51 and the compensating lead wire 52 are not disconnected, the DC voltage generated between the connection terminals B1 and B2 is a voltage value obtained by adding the thermoelectromotive force generated by the temperature sensor and the voltage drop of the resistor.

  On the other hand, when a disconnection (for example, the cutting point P1 or the cutting point P2) occurs in the temperature sensors of the thermocouple 51 and the compensation lead wire 52, the DC voltage generated between the connection terminals B1 and B2 is the reference DC power supply Vrf. Voltage.

  The amplifier 53 amplifies the voltage value obtained by adding the thermoelectromotive force generated between the connection terminals B1 and B2 and the voltage drop of the resistor, or the voltage of the reference DC power supply Vrf with a predetermined gain (for example, gain G1), and there is no disconnection. The temperature detection voltage VD in the state or the temperature detection voltage VH in the disconnection state is output.

  Note that the temperature detection voltage VD in the absence of disconnection from the presence / absence of disconnection becomes a value (VD << VH) that is much smaller than the temperature detection voltage VH in the disconnection state. The disconnection of the temperature sensor is detected from the temperature and the temperature detection voltage VH.

  The display 54 converts the temperature detection voltage VD into a corresponding temperature and displays the temperature numerically on a liquid crystal display (LCD) or the like.

  The comparator 55 compares the temperature detection voltage VH with a preset reference value, and outputs a disconnection signal HS when the temperature detection voltage VH exceeds the reference value.

  FIG. 8 shows a temperature detection voltage waveform diagram of an input circuit of a conventional thermocouple. In FIG. 8, when the temperature sensors of the thermocouple 51 and the compensating lead wire 52 are normal and there is no disconnection, the temperature detection voltage VD is a resistance voltage drop (error) to the temperature detection voltage VT corresponding to the thermoelectromotive force generated by the temperature sensor. ) It is detected by a value obtained by adding ΔV.

  On the other hand, when the temperature sensors of the thermocouple 51 and the compensating lead wire 52 are disconnected, the temperature detection voltage VH becomes a large value corresponding to the reference DC power supply Vrf, and is a value much larger than the temperature detection voltage VD <VH >> VD>. become.

  Further, as disclosed in “Patent Document 1”, the conventional non-contact temperature detecting device uses a temperature sensor having a sensor element such as a thermopile to switch in series with the resistor R having the configuration shown in FIG. The device is connected, the switch element is controlled to open and close by a microcomputer, temperature measurement is performed while the switch is open, and disconnection detection of the sensor is performed while the switch is closed .

Therefore, since a direct current is not passed during the temperature measurement period, a true value VT that does not include the error ΔV is detected, and during the disconnection detection period, if the temperature sensor is in a disconnected state, the true value VT is exceeded. A much larger voltage value VH <VH >>VD> can be detected.
JP 2001-153726 A (see FIG. 1)

  The conventional thermocouple input circuit has a configuration in which a minute current Is is passed through the temperature sensor to detect disconnection, and the temperature detection and disconnection detection are performed at the same time. Therefore, the temperature detection voltage VD has a resistance voltage drop due to the minute current IS. The accompanying error voltage ΔV is included, and there is a problem that the true temperature detection voltage VT accompanying the thermoelectromotive force cannot be obtained.

  If the error voltage ΔV is corrected, a true temperature detection voltage VT can be obtained. However, the management of the reference DC power supply Vrf and the measurement of the compensation conductor resistance r according to the types and lengths X of the compensation conductor L1 and the compensation conductor L2 can be performed. Thus, the error voltage ΔV must be set in advance, and there is a problem that requires complicated work and management.

  Further, since the non-contact temperature detection device disclosed in “Patent Document 1” performs temperature measurement and disconnection detection separately, temperature measurement without error is possible, but the temperature measurement period and disconnection detection period are determined. Switching device, microcomputer for controlling switching of the switching device, means for executing temperature measurement and disconnection detection in synchronization with the switching of the switching device are required, and when applied to the thermocouple input circuit of the present invention, There is a basic problem of large scale and complicated configuration.

  The present invention has been made to solve such a problem, and the object thereof is not to affect the temperature detection value of the thermoelectromotive force (DC voltage) using an AC signal, and has a simple configuration and rough design. An object of the present invention is to provide a thermocouple input circuit excellent in convenience capable of detecting disconnection.

  In order to solve the above problems, an input circuit of a thermocouple according to the present invention is an input of a thermocouple that detects the temperature by converting the temperature of an object into a corresponding thermoelectromotive force (DC voltage) by connecting a thermocouple and a compensating conductor. In the circuit, when an AC signal is applied to the thermocouple and the compensation lead, and the disconnection occurs in the thermocouple or the compensation lead, based on the change in the AC signal superimposed on the thermoelectromotive force (DC voltage) converted by the thermocouple A disconnection detecting means for detecting disconnection is provided.

  In the thermocouple input circuit according to the present invention, when an AC signal is applied to the thermocouple and the compensating lead wire, and the thermocouple or the compensating lead wire is disconnected, it is superimposed on the thermoelectromotive force (DC voltage) converted by the thermocouple. Because it is equipped with a disconnection detection means that detects disconnection based on the change in the AC signal, the thermoelectromotive force (DC voltage) value converted from the temperature can be accurately detected when detecting the temperature of the object, and a thermocouple or compensation When the conducting wire is disconnected, the disconnection can be reliably determined from the state in which the AC signal is changed.

  Further, the disconnection detecting means according to the present invention includes a signal generating means for generating an AC signal, a thermoelectromotive force (DC voltage) converted by the thermocouple and an amplifying means for amplifying the AC signal, and an AC signal amplified by the amplifier. It is characterized by comprising a disconnection determining means for comparing a reference level and determining a disconnection and outputting a disconnection signal when the amplified AC signal exceeds the reference level.

  The disconnection detecting means according to the present invention comprises: a signal generating means for generating an AC signal; a thermoelectromotive force (DC voltage) converted by a thermocouple; an amplifying means for amplifying the AC signal; an AC signal amplified by the amplifier; and a reference level When the amplified AC signal exceeds the reference level, the disconnection determining means for determining the disconnection and outputting the disconnection signal is provided, so that the disconnection of the thermocouple or the compensating lead wire is amplified with the AC signal, This can be determined by comparing the amplified AC signal with a reference level.

  Furthermore, the signal generating means according to the present invention generates an AC signal that is not limited to frequency and level.

  Since the signal generating means according to the present invention generates an AC signal that is not limited to frequency and level, the frequency, signal level, or pulse width (duty ratio) of the AC signal is arbitrarily selected when the AC signal is a pulse. Can be set.

  Moreover, the disconnection determination means according to the present invention is characterized by comprising a comparator.

  Since the disconnection determination means according to the present invention includes the comparator, the disconnection can be determined only by comparing the AC signal with the reference voltage value.

  Furthermore, the disconnection detecting means according to the present invention is applied to a temperature controller.

  Since the disconnection detecting means according to the present invention is applied to the temperature controller, it is not necessary to correct the temperature detection value of the temperature controller, the AC signal is not limited, and highly accurate temperature detection and reliable disconnection determination are simplified. Can be

  In the thermocouple input circuit according to the present invention, when an AC signal is applied to the thermocouple and the compensating lead wire, and the thermocouple or the compensating lead wire is disconnected, it is superimposed on the thermoelectromotive force (DC voltage) converted by the thermocouple. Because it is equipped with a disconnection detection means that detects disconnection based on the change in the AC signal, the thermoelectromotive force (DC voltage) value converted from the temperature can be accurately detected when detecting the temperature of the object, and a thermocouple or compensation When the conductor is disconnected, the disconnection can be reliably determined from the state in which the AC signal is changed, and convenience can be improved with a simple configuration and a rough design using the AC signal.

  Further, the disconnection detecting means according to the present invention includes a signal generating means for generating an AC signal, a thermoelectromotive force (DC voltage) converted by the thermocouple and an amplifying means for amplifying the AC signal, and an AC signal amplified by the amplifier. The reference level is compared, and when the amplified AC signal exceeds the reference level, the disconnection judging means for judging the disconnection and outputting the disconnection signal is provided. Therefore, the disconnection of the thermocouple or the compensation lead wire is amplified. Thus, it can be determined by comparing the amplified AC signal with a reference level, and the accuracy of temperature detection and the ease of disconnection determination can be appealed.

  Furthermore, since the signal generating means according to the present invention generates an AC signal that is not limited to the frequency and level, the frequency of the AC signal, the signal level, or the pulse width (duty ratio) is included when the AC signal is a pulse. It can be set arbitrarily, there is no restriction on the AC signal, and the circuit can be simplified.

  Moreover, since the disconnection determination means according to the present invention includes a comparator, it is possible to determine disconnection only by comparing the AC signal with the reference level, and it is possible to determine disconnection extremely easily.

  Further, since the disconnection detecting means according to the present invention is applied to the temperature controller, it is not necessary to correct the temperature detection value of the temperature controller, there is no restriction on the AC signal, high-accuracy temperature detection, and reliable disconnection determination. Can be simplified, and the ease of use of the temperature controller can be appealed.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram showing an embodiment of a thermocouple input circuit according to the present invention. In FIG. 1, a thermocouple input circuit 1 includes a thermocouple 2, a temperature sensor in which a compensation conductor 3 composed of a compensation conductor L1 and a compensation conductor L2 is connected by connection terminals A1 and A2, a disconnection detecting means 4, a temperature It comprises output means 5 and notification means 6.

  Compensation lead 3 comprises compensation lead L1 and compensation lead L2 made of an alloy material having the same or similar characteristics as thermocouple 2, and is connected by extending length X between thermocouple 2 and connection terminals B1 and B2. To do. The compensation lead L1 and the compensation lead L2 are determined by an alloy material and have a compensation lead resistance r corresponding to the length X.

  The temperature sensor composed of the thermocouple 2 and the compensating conductor 3 generates a thermoelectromotive force (DC voltage) VK corresponding to the temperature detected by the thermocouple 2 at both ends of the connection terminals B1 and B2.

  The disconnection detection means 4 applies an AC signal to the thermocouple 2 and the compensation lead wire 3, and when the disconnection occurs in the thermocouple 2 or the compensation lead wire 3, the disconnection detection means 4 generates the thermoelectromotive force (DC voltage) VK converted by the thermocouple 2. Disconnection is detected based on the change of the superimposed AC signal.

  The disconnection detection unit 4 includes a signal generation unit 7, an amplification unit 8, and a disconnection determination unit 9. The signal generating means 7 is composed of an oscillator that generates an AC signal such as a differential waveform signal obtained by differentiating a sine wave signal or a pulse signal such as a clock pulse with a differentiation circuit or the like. The frequency and level of the sine wave signal or pulse signal can be set arbitrarily. The duty ratio of the pulse signal is also set arbitrarily. This is because the AC signal may be used for detecting whether or not the AC current IK is flowing in the disconnection detection of the temperature sensor (thermocouple 2 + compensating lead 3). It is based on the fact that it is not necessary to set such as accurately.

  As described above, the signal generating means 7 according to the present invention generates an AC signal (AC voltage VS) that is not limited to the frequency and level. Therefore, the frequency, signal level, or AC signal (AC signal) of the AC signal (AC voltage VS) When the voltage VS) is a pulse, it can be arbitrarily set including the pulse width (duty ratio), there is no restriction on the AC signal, the design is rough, and the circuit can be simplified. .

  An AC current IK is passed from the AC voltage VS of the generated AC signal to the temperature sensor (comprising the thermocouple 2 and the compensating conductor 3) through the capacitor C and the resistor R1. The alternating current IK is the signal generation means 7 → capacitor C → resistor R1 → connection terminal B1 → compensation lead L1 → connection terminal A1 → thermocouple 2 → connection terminal A2 → compensation lead L2 → connection terminal B2 → ground (GND). It flows in the current path. The resistor R1 is set to a resistance value sufficiently larger than the resistance of the compensation conductor L1, the compensation conductor resistance r of the compensation conductor L2, and the resistance of the thermocouple 2, and the alternating current IK is set to, for example, μA (microampere) or mA (milliampere). ) Make an order.

  In a state where the thermocouple 2 and the compensating conductor 3 are not disconnected, an alternating current component VA (alternating voltage drop) is generated between the connection terminals B1 and B2 as the alternating current IK flows. The AC component VA is the product of the combined resistance of the compensation conductor resistance 2r of the compensation conductor L1 and the compensation conductor L2 and the resistance value of the thermocouple 2 and the AC current IK.

  On the other hand, when the thermocouple 2 or the compensating lead wire 3 is disconnected (for example, the cutting point P1 or the cutting point P2), the alternating current IK does not flow and the alternating voltage VS appears between the connection terminals B1 and B2.

  The amplifying means 8 is composed of an operational amplifier (operational amplifier) driven by a + VC voltage and a -VC voltage, and has two input terminals connected to connection terminals B1 and B2, respectively. The amplification means 8 is set to a sufficiently large predetermined gain.

  The amplifying means 8 amplifies the thermoelectromotive force (DC voltage) VK and the AC component VA that are input without disconnection of the thermocouple 2 and the compensating lead wire 3, and outputs the amplified temperature detection voltage VT and AC component VO as temperature. Supply to means 5. Further, the AC component VO is supplied to the disconnection determining means 9 through the capacitor C1.

  FIG. 2 is an output voltage waveform diagram of an embodiment of the amplifying means according to the present invention. (A) The figure shows the output voltage waveform diagram when there is no disconnection, (b) The figure shows the output voltage waveform diagram when the disconnection occurs. (A) In the figure, the thermoelectromotive force (DC voltage) VK which is an input of the amplifying means 8 is amplified to become a temperature detection voltage VT. On the other hand, the AC component VA is also amplified to become an AC component VO. In the present embodiment, a case where a sine wave is used as an AC signal is shown, and the DC temperature detection voltage VT and the AC component VO appear on the plus (+) side. When the amplitude of the AC component VO is large, a part of the waveform may appear on the minus (−) side.

  (B) In the figure, the AC voltage VS which is the input of the amplifying means 8 is amplified and the sine wave is saturated with the drive power sources + VC and -VC of the amplifying means 8 and appears as an AC component VH close to a rectangular wave.

  The disconnection determination means 9 is composed of a rectification / smoothing circuit and a comparator, converts the AC component VO that is not disconnected or the AC component VH that is disconnected from the amplification means 8 into a DC component, and compares the DC component with a reference level. If the DC component exceeds the reference level, it is determined that the disconnection state has occurred, and the disconnection signal HD is output.

  FIG. 3 is a block diagram showing the principal part of one embodiment of the disconnection judging means according to the present invention. In FIG. 3, the disconnection determining means 9 includes a full-wave rectifier circuit constituted by a diode bridge DB, a smoothing capacitor C2, and a comparator 10, and rectifies and smoothes the AC component VO or AC component VH supplied from the amplifying means 8. The DC component VO1 corresponding to the AC component VO or the DC component VH1 corresponding to the AC component VH is used, and the DC component VO1 or DC component VH1 is supplied to the comparator 10.

  The comparator 10 compares the DC component VO1 or the DC component VH1 with the reference level Vα, and generates a disconnection signal HD when the DC component VO1 and the DC component VH1 exceed the reference level Vα (VO1> Vα, VH1> Vα). Then, the disconnection signal HD is provided to the notification means 6.

  On the other hand, the comparator 10 does not generate the disconnection signal HD when the DC component VO1 and the DC component VH1 are below the reference level Vα (VO1 ≦ Vα, VH1 ≦ Vα).

  Since the disconnection signal HD is not generated in the state where disconnection does not occur and the disconnection signal HD is generated in the state where disconnection occurs, the reference level Vα is set to be higher than the DC component VO1 and lower than the DC component VH1 (VO1 < Vα <VH1), for example, the reference level Vα = VC / 2 is set.

  Thus, the disconnection detecting means 4 according to the present invention amplifies the signal generating means 7 for generating an AC signal, the thermoelectromotive force (DC voltage) VK and the AC signal (AC component VA) converted by the thermocouple 2. The amplifying means 8 and the AC signal (VO, VH) amplified by the amplifier 8 are compared with the reference level Vα, and when the amplified AC signal exceeds the reference level, the disconnection is determined and the disconnection signal HD is output. Therefore, the disconnection of the thermocouple 2 or the compensating conductor 3 can be determined by amplifying the AC signal (AC voltage VS) and comparing the amplified AC signal with the reference level Vα. It is possible to appeal the accuracy and ease of disconnection determination.

  Further, since the disconnection determination means 9 according to the present invention includes the comparator 10, it is possible to determine disconnection only by comparing the AC signal (AC component VH) with the reference level Vα, and it is very easy to determine disconnection. be able to.

  Returning to FIG. 1, the temperature output means 5 includes a correspondence table between the temperature detection voltage VT and the temperature data TD, converts the temperature detection voltage VT supplied from the amplification means 8 into the temperature data TD in the correspondence table, and converts the temperature data TD into the temperature data TD. Provide to the notification means 6.

  FIG. 4 is a block diagram showing the principal part of an embodiment of the temperature output means according to the present invention. In FIG. 4, the temperature output unit 5 includes a memory access unit 11 and a temperature storage unit 12. The memory access means 11 takes in the temperature detection voltage VT supplied from the amplification means 8, accesses the temperature storage means 12, reads the temperature data TD corresponding to the temperature detection voltage VT from the temperature storage means 12, and reads the read temperature. Data TD is provided to the notification means 6.

  The temperature storage means 12 is composed of a rewritable memory such as an EEPROM, stores a correspondence table between the temperature detection voltage VT and the temperature data TD in advance, and if the memory access means 11 accesses the temperature detection voltage VT, the temperature detection means 12 Temperature data TD corresponding to the voltage VT is provided to the memory access means 11.

  FIG. 5 is a block diagram of an embodiment of the notification means according to the present invention. In FIG. 5, the notification means 6 includes a display driving means 13 for displaying the temperature data TD provided from the temperature output means 5 and an LCD display 14 for displaying the temperature data TD. The notification unit 6 includes a speaker SP that outputs the disconnection signal HD provided from the disconnection determination unit 9 by voice, and a light-emitting diode LED that displays the signal by lighting or blinking.

  The display drive means 13 converts the temperature data TD into a drive signal SD in a format matched to the LCD (liquid crystal device) and supplies it to the LCD display 14. The LCD display 14 receives the thermocouple 2 based on the drive signal SD. Displays the temperature detected by.

  As described above, the thermocouple input circuit 1 according to the present invention applies an AC signal to the thermocouple 2 and the compensating conductor 3, and when the thermocouple 2 or the compensating conductor 3 is disconnected, the thermocouple 2 is provided with disconnection detection means 4 for detecting disconnection based on the change of the AC signal (VA → VS) superimposed on the thermoelectromotive force (DC voltage) VK converted, so that the temperature is converted when detecting the temperature of the object. The detected thermoelectromotive force (DC voltage) VT value can be accurately detected, and when the thermocouple 2 or the compensating lead wire 3 is disconnected, the disconnection can be reliably determined from the state in which the AC signal has changed (VO → VH). Convenience can be improved with a simple configuration and rough design using an AC signal.

  In the present embodiment, the temperature sensor is composed of the thermocouple 2 and the compensating lead wire 3. However, if the sensor can detect a physical quantity of the object and convert it into a DC voltage, the thermocouple input circuit of the present invention is used. Can be applied.

  Next, an example in which the thermocouple input circuit according to the present invention is applied to a temperature controller will be described. FIG. 6 is a block diagram of an embodiment of a temperature controller to which the thermocouple input circuit according to the present invention is applied. In FIG. 6, the temperature controller 15 includes a temperature setting unit 16, a temperature control calculation unit 17, an SSR drive unit 18, a current measurement unit 19, and a thermocouple input circuit 20, and an SSR (solid state circuit) with a predetermined drive amount. Relay) 22 is turned on / off, AC power supply VAC is intermittently connected, heater current IH is supplied to heater HT of furnace 24, and the temperature of semiconductor wafer 25 in the furnace is controlled by thermocouple input circuit 20 having thermocouple 21. By detecting and measuring, the predetermined drive amount is controlled so that the measured temperature of the semiconductor wafer 25 becomes a preset temperature, and the AC heater current IH flowing through the heater HT is detected and measured.

  In the temperature controller 15, the SSR driving unit 18 outputs a driving amount corresponding to the temperature set in advance by the temperature setting unit 16, and drives the SSR (solid state relay) 22 on / off with the driving amount.

  The SSR 22 is driven on / off with a driving amount, and the AC power source VAC is intermittently supplied, and a heater current IH corresponding to the driving amount is supplied to the heater HT of the furnace 24. The heater current IH flows through the heater HT, the furnace 24 is heated to warm the semiconductor wafer 25, the temperature of the semiconductor wafer 25 is detected by the thermocouple 21, and the detected temperature is provided to the input circuit 20 of the thermocouple.

  The thermocouple input circuit 20 measures the temperature provided from the thermocouple 21 and supplies the measured temperature to the temperature control calculation unit 17. The temperature control calculation unit 17 calculates a temperature deviation between the set temperature set by the temperature setting unit 16 and the temperature supplied from the thermocouple input circuit 20 and supplies the temperature deviation to the SSR drive unit 18.

  The SSR drive unit 18 adjusts the drive amount corresponding to the temperature deviation supplied from the temperature control calculation unit 17 and drives the SSR (solid state relay) 22 on / off with the adjusted drive amount, The heater current IH flowing through the heater HT is adjusted to adjust the temperature of the semiconductor wafer 25 in the furnace 24.

  Again, the thermocouple 21 detects the temperature of the semiconductor wafer 25, the thermocouple input circuit 20 measures the temperature, the temperature control calculation unit 17 calculates the temperature deviation, and the SSR drive unit 18 drives corresponding to the temperature deviation. The driving of the SSR 22 with the amount is repeated, and when the measured temperature matches the set temperature, the driving amount becomes a constant value and the heater current IH also becomes a constant value. The set temperature, measurement temperature, and temperature deviation system forms a feedback (negative feedback) loop.

  The current value measuring means 19 is a maximum value obtained by detecting a heater current IH of an alternating current flowing through the heater HT with an AC voltage by the current transformer 23 and converting a peak value on the positive electrode side from a detected zero value to a digital value. Since the current is measured as a current, the minute current value of the heater current IH is also measured linearly.

  As described above, since the disconnection detecting means according to the present invention is applied to the temperature controller 15, correction of the temperature detection value of the temperature controller 15 is not required, the AC signal is not restricted, and highly accurate temperature detection and Reliable disconnection determination can be simplified and the ease of use of the temperature controller can be appealed.

  The thermocouple input circuit according to the present invention easily performs temperature detection using a DC voltage and temperature sensor disconnection detection using an AC signal by applying an AC signal to a temperature sensor composed of a thermocouple and a compensating conductor. The present invention can be applied to detection of disconnection of any sensor that detects a physical quantity with a DC voltage and a device including the sensor.

1 is a block diagram of a thermocouple input circuit according to an embodiment of the present invention. One embodiment of amplifying means according to the present invention Output voltage waveform diagram Block diagram of one embodiment of a disconnection determining means according to the present invention Block diagram of main part of one embodiment of temperature output means according to the present invention Configuration of one embodiment of notification means according to the present invention 1 is a block diagram of an embodiment of a temperature controller to which a thermocouple input circuit according to the present invention is applied. Temperature detection voltage diagram of conventional thermocouple input circuit Temperature detection voltage waveform diagram of conventional thermocouple input circuit

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Input circuit of thermocouple 2,21 Thermocouple 3 Compensation lead 4 Disconnection detection means 5 Temperature output means 6 Notification means 7 Signal generation means 8 Amplification means 9 Disconnection determination means 10 Comparator 11 Memory access means 12 Temperature storage means 13 Display drive means DESCRIPTION OF SYMBOLS 14 LCD display device 15 Temperature controller 16 Temperature setting part 17 Temperature control calculating part 18 SSR drive part 19 Current measurement part 22 SSR (solid state relay)
23 Current transformer 24 Furnace 25 Semiconductor wafer X Compensation lead length r Compensation lead resistance DB Diode bridge SP Speaker LED Light emitting diode VK Thermoelectromotive force (DC voltage)
VS AC voltage IK AC current VA, VO, VH AC component VT Temperature detection voltage Vα Reference level TD Temperature data HD Disconnection signal

Claims (5)

In the input circuit of the thermocouple that connects the thermocouple and the compensating lead, converts the temperature of the object into the corresponding thermoelectromotive force (DC voltage) and detects it,
When an AC signal is applied to the thermocouple and the compensation conductor, and a disconnection occurs in the thermocouple or the compensation conductor, the change in the AC signal superimposed on the thermoelectromotive force (DC voltage) converted by the thermocouple An input circuit for a thermocouple, characterized by comprising disconnection detecting means for detecting disconnection on the basis thereof. The disconnection detecting means includes a signal generating means for generating an AC signal, a thermoelectromotive force (DC voltage) converted by the thermocouple and an amplifying means for amplifying the AC signal, an AC signal amplified by the amplifier and a reference level. 2. The thermocouple input circuit according to claim 1, further comprising: a disconnection determination unit configured to determine disconnection and output a disconnection signal when the compared and amplified AC signal exceeds a reference level. 3. The thermocouple input circuit according to claim 2, wherein the signal generating means generates an AC signal that is not limited to a frequency and a level. The thermocouple input circuit according to claim 2, wherein the disconnection determination means includes a comparator. The thermocouple input circuit according to claim 1, wherein the disconnection detecting means is applied to a temperature controller.

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