Cold junction compensation circuit of thermocouple

Abstract

The utility model is suitable for the field of temperature sensors, and provides a cold junction compensation circuit of a thermocouple, which comprises a signal acquisition module, a cold junction compensation module and a signal processing module, the signal acquisition module is used for acquiring temperature difference voltage generated by the thermocouple; the cold end compensation module comprises a resistor R4, a resistor R7, a variable resistor RC1 and a capacitor C8 and is used for adjusting compensation voltage according to the temperature of a cold end; one end of the resistor R4 is connected with a second signal input end of the signal processing module through the resistor R7 and is connected with a ground wire through the variable resistor RC1, and the resistor R4 is used for adjusting the ratio of the resistor R4 to the variable resistor RC1 according to the temperature of a cold end so as to adjust compensation voltage; and the signal processing module is used for outputting compensated processing voltage according to the compensation voltage adjusted by the cold junction compensation module and the temperature difference voltage generated by the thermocouple. The thermocouple cold junction compensation circuit solves the problem that a thermocouple cold junction compensation design circuit is high in cost.

Description

Technical Field

[0001] The utility model belongs to the field of temperature sensors, and in particular relates to a cold end compensation circuit of a thermocouple. Background Art

[0002] Thermocouples are commonly used temperature measuring elements in temperature measuring instruments. The working principle of thermocouples is based on the Seebeck effect, that is, when there is a temperature difference between the two ends of two different metals, a voltage will be generated between the metals. When the cold end is introduced into the circuit board, since the soldering point on the circuit board is composed of two different components, copper and tin, the potential at this soldering point will also be affected by the circuit board or ambient temperature, thereby interfering with the measured value on the probe.

[0003] At present, the cold end compensation of thermocouples is generally carried out by chip compensation or software compensation.

[0004] The circuit cost of using chip compensation or software compensation is relatively high, and there is a problem that the circuit cost of thermocouple cold end compensation design is relatively high. Utility Model Content

[0005] The purpose of the embodiment of the utility model is to provide a cold end compensation circuit of a thermocouple, aiming to solve the problem of high cost of designing the cold end compensation circuit of the thermocouple.

[0006] The utility model is implemented in this way: a cold end compensation circuit of a thermocouple, the cold end compensation circuit of the thermocouple comprises: a signal acquisition module, a cold end compensation module and a signal processing module;

[0007] The output end of the signal acquisition module is connected to the first signal input end of the signal processing module, and is used to obtain the temperature difference voltage generated by the thermocouple;

[0008] The cold end compensation module includes a resistor R4, a resistor R7, a variable resistor RC1 and a capacitor C8, and is used to adjust the compensation voltage according to the temperature of the cold end;

[0009] One end of the resistor R4 is connected to the second signal input end of the signal processing module through the resistor R7, and is connected to the ground line through the variable resistor RC1, so as to adjust the ratio of the resistor R4 to the variable resistor RC1 according to the temperature of the cold end, thereby adjusting the compensation voltage;

[0010] The capacitor C8 is arranged between the second signal input terminal of the signal processing module and the ground line;

[0011] The signal processing module is used to output a compensated processing voltage according to the compensation voltage adjusted by the cold end compensation module and the temperature difference voltage generated by the thermocouple.

[0012] Preferably, the variable resistor RC1 is arranged near the cold end of the thermocouple.

[0013] Preferably, the variable resistor RC1 is a PT100 positive temperature coefficient resistor.

[0014] Preferably, the signal acquisition module includes a resistor R1, a resistor R2, a capacitor C1, a resistor R5 and a diode D1;

[0015] One end of the resistor R1 is connected to the cold end of the thermocouple, and the other end is connected to the first signal input end of the signal processing module;

[0016] One end of the resistor R2 is connected to the hot end of the thermocouple, and the other end is connected to the ground wire;

[0017] One end of the capacitor C1 is connected to the first signal input end of the signal processing module, and the other end is connected to the ground line;

[0018] One end of the resistor R5 is connected to the first signal input end of the signal processing module, and the other end is connected to the ground line;

[0019] The anode of the diode D1 is connected to the first signal input terminal of the signal processing module, and the cathode is connected to the ground line.

[0020] Preferably, the signal processing module includes an operational amplifier U1, a resistor R3, a resistor R6, an output terminal J3, a capacitor C3, a capacitor C4, a capacitor C5, a capacitor C6 and a capacitor C7;

[0021] The -IN pin of the operational amplifier U1 is connected to the end of the resistor R1 that is not connected to the cold end of the thermocouple, the +IN pin is connected to the end of the resistor R7 that is not connected to the resistor R4, the +VS pin is connected to the ground wire through the capacitor C3, the VOUT pin is connected to the output terminal J3 through the resistor R6, the REF pin is connected to the ground wire, and the -VS pin is connected to the ground wire through the capacitor C4;

[0022] The resistor R3 is connected in series between the two RG pins of the operational amplifier U1;

[0023] The capacitor C5 is arranged between the +IN pin of the operational amplifier U1 and the ground line;

[0024] The capacitor C6 is arranged between the resistor R6 and the ground line;

[0025] The capacitor C7 is disposed between the -IN pin of the operational amplifier U1 and the VOUT pin of the operational amplifier U1.

[0026] Preferably, the cold end compensation circuit of the thermocouple further includes a capacitor C2;

[0027] The capacitor C2 is disposed between the −IN pin of the operational amplifier U1 and the +IN pin of the operational amplifier U1 .

[0028] Preferably, the cold end compensation circuit of the thermocouple further includes a power supply module and a main control module;

[0029] The power supply module is connected to the end of the resistor R4 that is not connected to the resistor R7, the +VS pin of the operational amplifier U1, and the main control module, and is used to provide a compensation voltage for the cold end compensation module and provide an operating voltage for the signal processing module and the main control module;

[0030] The signal input end of the main control module is connected to the output terminal J3, and is used to determine the temperature of the thermocouple according to the processing voltage output by the signal processing module.

[0031] The cold-end compensation circuit of a thermocouple provided by the embodiment of the utility model has the following beneficial effects:

[0032] First, the signal acquisition module obtains the temperature difference voltage generated by the thermocouple, and then the voltage division size of the resistor R4 is changed by adjusting the ratio of the resistor R4 and the variable resistor RC1, so as to adjust the compensation voltage, and finally the signal processing module outputs the compensated processing voltage according to the compensation voltage adjusted by the cold end compensation module and the temperature difference voltage generated by the thermocouple. In this way, the redundant circuit required for chip compensation or software compensation is not required, and only the resistor is needed to perform cold end compensation on the thermocouple, which solves the problem of high design cost of the thermocouple. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A structural diagram of a cold-end compensation circuit of a thermocouple provided in an embodiment of the utility model;

[0034] Figure 2 A partial circuit diagram of a cold-end compensation circuit for a thermocouple provided in an embodiment of the utility model. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solution and advantages of the utility model more clear, the utility model is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the utility model and are not used to limit the utility model.

[0036] The specific implementation of the present utility model is described in detail below in conjunction with specific embodiments.

[0037] like Figure 1 , Figure 2As shown, it is a structural diagram of a cold end compensation circuit of a thermocouple provided by an embodiment of the utility model, comprising: a signal acquisition module, a cold end compensation module and a signal processing module;

[0038] The output end of the signal acquisition module is connected to the first signal input end of the signal processing module, and is used to obtain the temperature difference voltage generated by the thermocouple;

[0039] The cold end compensation module includes a resistor R4, a resistor R7, a variable resistor RC1 and a capacitor C8, and is used to adjust the compensation voltage according to the temperature of the cold end;

[0040] One end of the resistor R4 is connected to the second signal input end of the signal processing module through the resistor R7, and is connected to the ground line through the variable resistor RC1, so as to adjust the ratio of the resistor R4 to the variable resistor RC1 according to the temperature of the cold end, thereby adjusting the compensation voltage;

[0041] The capacitor C8 is arranged between the second signal input terminal of the signal processing module and the ground line;

[0042] The signal processing module is used to output a compensated processing voltage according to the compensation voltage adjusted by the cold-end compensation module and the temperature difference voltage generated by the thermocouple.

[0043] In the embodiment of the utility model, there are various types of thermocouples, and a T-type thermocouple is preferred.

[0044] In the embodiment of the utility model, the temperature difference voltage generated by the thermocouple is related to the temperature difference between the hot end and the cold end. The smaller the temperature difference, the smaller the temperature difference. Theoretically, the cold end of the thermocouple should be 0°.

[0045] In the embodiment of the present invention, when the cold end temperature rises, the resistance of the variable resistor RC1 rises, and the shared voltage becomes larger, while the voltage of the resistor R4 becomes smaller as the resistance of the variable resistor RC1 increases, so the compensation voltage becomes smaller.

[0046] In an embodiment of the utility model, the signal processing module processes the compensation voltage adjusted by the cold end compensation module and the temperature difference voltage generated by the thermocouple based on the principle of an operational amplifier. When the temperature of the hot end of the thermocouple remains unchanged, the output processing voltage cannot change. When the temperature of the cold end of the thermocouple rises, the temperature difference voltage will decrease, and the compensation voltage at this time should also decrease, so that the output processing voltage will remain unchanged, that is, the cold end compensation of the thermocouple is performed by changing the compensation voltage so that the processing voltage output by the signal processing module remains unchanged, and the processing voltage corresponds to the temperature of the hot end of the thermocouple.

[0047] The cold end compensation circuit of a thermocouple provided by the embodiment of the utility model first obtains the temperature difference voltage generated by the thermocouple through the signal acquisition module, and then changes the voltage division size of the resistor R4 by adjusting the ratio of the resistor R4 and the variable resistor RC1, thereby adjusting the compensation voltage, and finally the signal processing module outputs the compensated processing voltage according to the compensation voltage adjusted by the cold end compensation module and the temperature difference voltage generated by the thermocouple. In this way, the redundant circuit required for chip compensation or software compensation is not required, and only resistors are needed to perform cold end compensation on the thermocouple, which solves the problem of high cost of designing circuits for cold end compensation of thermocouples.

[0048] As a preferred embodiment of the present utility model, the variable resistor RC1 is arranged near the cold end of the thermocouple.

[0049] In the embodiment of the present invention, in order to synchronize with the cold end temperature and achieve an ideal cold end compensation effect, the variable resistor RC1 is arranged close to the cold end of the thermocouple.

[0050] As a preferred embodiment of the present invention, the variable resistor RC1 is a PT100 positive temperature coefficient resistor.

[0051] In the embodiment of the utility model, when the resistance of the PT100 positive temperature coefficient resistor is 100 ohms at 0 degrees Celsius, its resistance will increase at an approximately uniform rate as the temperature rises.

[0052] like Figure 2 As shown, as a preferred embodiment of the utility model, the signal acquisition module includes a resistor R1, a resistor R2, a capacitor C1, a resistor R5 and a diode D1;

[0053] One end of the resistor R1 is connected to the cold end of the thermocouple, and the other end is connected to the first signal input end of the signal processing module;

[0054] One end of the resistor R2 is connected to the hot end of the thermocouple, and the other end is connected to the ground wire;

[0055] One end of the capacitor C1 is connected to the first signal input end of the signal processing module, and the other end is connected to the ground line;

[0056] One end of the resistor R5 is connected to the first signal input end of the signal processing module, and the other end is connected to the ground line;

[0057] The anode of the diode D1 is connected to the first signal input terminal of the signal processing module, and the cathode is connected to the ground line.

[0058] In the embodiment of the utility model, the end of the resistor R1 connected to the first signal input end of the signal processing module is the output end of the signal acquisition module.

[0059] In the embodiment of the present utility model, Figure 2 As shown, the cold end of the thermocouple is terminal J1, and the hot end of the thermocouple is terminal J2.

[0060] like Figure 2 As shown, as a preferred embodiment of the utility model, the signal processing module includes an operational amplifier U1, a resistor R3, a resistor R6, an output terminal J3, a capacitor C3, a capacitor C4, a capacitor C5, a capacitor C6 and a capacitor C7;

[0061] The -IN pin of the operational amplifier U1 is connected to the end of the resistor R1 that is not connected to the cold end of the thermocouple, the +IN pin is connected to the end of the resistor R7 that is not connected to the resistor R4, the +VS pin is connected to the ground wire through the capacitor C3, the VOUT pin is connected to the output terminal J3 through the resistor R6, the REF pin is connected to the ground wire, and the -VS pin is connected to the ground wire through the capacitor C4;

[0062] The resistor R3 is connected in series between the two RG pins of the operational amplifier U1;

[0063] The capacitor C5 is arranged between the +IN pin of the operational amplifier U1 and the ground line;

[0064] The capacitor C6 is arranged between the resistor R6 and the ground line;

[0065] The capacitor C7 is disposed between the -IN pin of the operational amplifier U1 and the VOUT pin of the operational amplifier U1.

[0066] In the embodiment of the present utility model, the model of the operational amplifier U1 may be AD8221.

[0067] In the embodiment of the present invention, the resistor R3 is used to adjust the gain effect of the operational amplifier U1.

[0068] In the embodiment of the utility model, the first signal input terminal of the signal processing module is the -IN pin of the operational amplifier U1; the second signal input terminal is the +IN pin of the operational amplifier U1; and the output terminal is the output terminal J3.

[0069] In the embodiment of the utility model, the temperature difference voltage and the compensation voltage input to the operational amplifier U1 and the processing voltage output by the operational amplifier U1 are essentially voltage signals.

[0070] In the embodiment of the utility model, the purpose of capacitor C7 is to optimize its frequency response characteristics through the advance compensation technology, reduce the noise caused by self-oscillation and other problems, and ensure that the operational amplifier can maintain a stable working state under various working conditions.

[0071] like Figure 2 As shown, as a preferred embodiment of the utility model, the cold end compensation circuit of the thermocouple further includes a capacitor C2;

[0072] The capacitor C2 is disposed between the −IN pin of the operational amplifier U1 and the +IN pin of the operational amplifier U1 .

[0073] In the embodiment of the utility model, capacitor C2 is connected between the output end of the signal acquisition module and the output end of the cold end compensation module in order to reduce or eliminate the influence of external interference signals on the input end of the operational amplifier, thereby playing the role of anti-interference and filtering.

[0074] As a preferred embodiment of the utility model, the cold end compensation circuit of the thermocouple further includes a power supply module and a main control module;

[0075] The power supply module is connected to the end of the resistor R4 that is not connected to the resistor R7, the +VS pin of the operational amplifier U1, and the main control module, and is used to provide a compensation voltage for the cold end compensation module and provide an operating voltage for the signal processing module and the main control module;

[0076] The signal input end of the main control module is connected to the output terminal J3, and is used to determine the temperature of the thermocouple according to the processing voltage output by the signal processing module.

[0077] In the embodiment of the utility model, the power module outputs a DC voltage of +15V.

[0078] In the embodiment of the present utility model, there are many ways for the main control voltage to determine the temperature of the thermocouple according to the processing voltage, such as a table lookup method.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A cold-end compensation circuit for a thermocouple, characterized in that: The cold end compensation circuit of the thermocouple comprises: a signal acquisition module, a cold end compensation module and a signal processing module; The output end of the signal acquisition module is connected to the first signal input end of the signal processing module, and is used to obtain the temperature difference voltage generated by the thermocouple; The cold end compensation module includes a resistor R4, a resistor R7, a variable resistor RC1 and a capacitor C8, and is used to adjust the compensation voltage according to the temperature of the cold end; One end of the resistor R4 is connected to the second signal input end of the signal processing module through the resistor R7, and is connected to the ground line through the variable resistor RC1, so as to adjust the ratio of the resistor R4 to the variable resistor RC1 according to the temperature of the cold end, thereby adjusting the compensation voltage; The capacitor C8 is arranged between the second signal input terminal of the signal processing module and the ground line; The signal processing module is used to output a compensated processing voltage according to the compensation voltage adjusted by the cold-end compensation module and the temperature difference voltage generated by the thermocouple.

2. The cold end compensation circuit of the thermocouple according to claim 1, characterized in that: The variable resistor RC1 is arranged near the cold end of the thermocouple.

3. The cold junction compensation circuit of the thermocouple according to claim 1, characterized in that: The variable resistor RC1 is a PT100 positive temperature coefficient resistor.

4. The cold junction compensation circuit of the thermocouple according to claim 1, characterized in that: The signal acquisition module includes a resistor R1, a resistor R2, a capacitor C1, a resistor R5 and a diode D1; One end of the resistor R1 is connected to the cold end of the thermocouple, and the other end is connected to the first signal input end of the signal processing module; One end of the resistor R2 is connected to the hot end of the thermocouple, and the other end is connected to the ground wire; One end of the capacitor C1 is connected to the first signal input end of the signal processing module, and the other end is connected to the ground line; One end of the resistor R5 is connected to the first signal input end of the signal processing module, and the other end is connected to the ground line; The anode of the diode D1 is connected to the first signal input terminal of the signal processing module, and the cathode is connected to the ground line.

5. The cold end compensation circuit of the thermocouple according to claim 4, characterized in that: The signal processing module includes an operational amplifier U1, a resistor R3, a resistor R6, an output terminal J3, a capacitor C3, a capacitor C4, a capacitor C5, a capacitor C6 and a capacitor C7; The -IN pin of the operational amplifier U1 is connected to the end of the resistor R1 that is not connected to the cold end of the thermocouple, the +IN pin is connected to the end of the resistor R7 that is not connected to the resistor R4, the +VS pin is connected to the ground wire through the capacitor C3, the VOUT pin is connected to the output terminal J3 through the resistor R6, the REF pin is connected to the ground wire, and the -VS pin is connected to the ground wire through the capacitor C4; The resistor R3 is connected in series between the two RG pins of the operational amplifier U1; The capacitor C5 is arranged between the +IN pin of the operational amplifier U1 and the ground line; The capacitor C6 is arranged between the resistor R6 and the ground line; The capacitor C7 is disposed between the -IN pin of the operational amplifier U1 and the VOUT pin of the operational amplifier U1.

6. The cold end compensation circuit of the thermocouple according to claim 5, characterized in that: The cold end compensation circuit of the thermocouple also includes a capacitor C2; The capacitor C2 is disposed between the −IN pin of the operational amplifier U1 and the +IN pin of the operational amplifier U1 .

7. The cold end compensation circuit of the thermocouple according to claim 5, characterized in that: The cold end compensation circuit of the thermocouple also includes a power supply module and a main control module; The power supply module is connected to the end of the resistor R4 that is not connected to the resistor R7, the +VS pin of the operational amplifier U1, and the main control module, and is used to provide a compensation voltage for the cold end compensation module and provide an operating voltage for the signal processing module and the main control module; The signal input end of the main control module is connected to the output terminal J3, and is used to determine the temperature of the thermocouple according to the processing voltage output by the signal processing module.

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