Cold junction compensation method for thermocouple thermodetector and thermocouple thermodetector

Abstract

The invention belongs to the technical field of thermocouple thermodetectors, and particularly relates to a thermocouple thermodetector cold junction compensation method and a thermocouple thermodetector, and the method comprises the steps: an MCU circuit obtains a temperature value Te of an NTC chip reading circuit, an AD value Vt of a measurement thermocouple, and an AD value Voffset of a compensation thermocouple; the MCU circuit calculates the AD value V of the thermocouple after compensation; a conversion voltage value vt is generated according to the temperature value Te of the NTC chip reading circuit; generating a voltage value v of the target temperature according to the compensated AD value V of the thermocouple and the converted voltage value vt; and generating a final temperature value T of the target temperature according to the voltage value v of the target temperature. According to the method, real-time compensation can be achieved through the NTC chip reading circuit and the compensation thermocouple in cooperation with a compensation algorithm, the precision is stabilized within + / -0.3 DEG C, and the method is easy to operate and use and low in manufacturing cost.

Description

Technical Field

[0001] The present application relates to the technical field of thermocouple thermometers, and in particular to a cold-end compensation method for a thermocouple thermometer and a thermocouple thermometer. Background Art

[0002] Thermocouple temperature measurement principles indicate that the thermoelectric potential is a single-valued function of the measured temperature only when the cold-junction temperature of the thermocouple remains constant. In practical applications, the cold-junction temperature of a thermocouple is not constant but can be affected by the heat generated by internal electronic components over time or by the user's handling, which can affect the thermocouple's temperature measurement accuracy. Several common cold-junction compensation methods for thermocouples exist, including: cold-junction constant temperature, compensation bridge, PN junction compensation, zero-point migration, compensation wire, and the AD592 cold-junction compensation method.

[0003] The cold-junction constant temperature method requires placing the thermocouple cold junction inside a constant temperature device. While this method can compensate for cold-junction temperature variations caused by the external environment, it cannot compensate for cold-junction temperature variations caused by heat generated by the instrument's internal electronic components. The compensation bridge and PN junction compensation methods exhibit hysteresis, preventing real-time compensation. They are also difficult to debug for multi-channel thermocouples and exhibit low integration. The zero-point migration and compensation wire methods, while capable of compensating for cold-junction temperature variations caused by the external environment, cannot compensate for cold-junction temperature variations caused by heat generated by the instrument's internal electronic components. The AD592 cold-junction compensation method cannot compensate for changes in the instrument's cold-junction temperature caused by heat generated by the instrument's internal electronic components or by the tester's hand temperature. Furthermore, the cost is high.

[0004] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may include information that does not constitute prior art known to ordinary technicians in the field.

[0005] Application Contents

[0006] In view of at least one of the above technical problems, the present application provides a cold-end compensation method for a thermocouple thermometer and a thermocouple thermometer.

[0007] In a first aspect, a cold-end compensation method for a thermocouple thermometer is provided, which is applied to a thermocouple thermometer. The thermocouple thermometer includes: a compensating thermocouple, a measuring thermocouple, a compensating measurement circuit, a target measurement circuit, an NTC chip reading circuit, and an MCU circuit. The compensating thermocouple is connected to the compensating measurement circuit. The compensating thermocouple is used to measure the internal temperature of the thermocouple thermometer. The measuring thermocouple is connected to the target measurement circuit. The MCU circuit is respectively connected to the compensating measurement circuit, the target measurement circuit, and the NTC chip reading circuit.

[0008] Methods include:

[0009] The MCU circuit obtains the temperature value Te of the NTC chip reading circuit, measures the AD value Vt of the thermocouple, and compensates the AD value Voffset of the thermocouple;

[0010] The MCU circuit calculates the compensation and measures the thermocouple AD value V;

[0011] Generate a conversion voltage value vt based on the temperature value Te of the circuit read by the NTC chip;

[0012] Generate the voltage value v of the target temperature based on the compensated measured thermocouple AD value V and the converted voltage value vt;

[0013] According to the voltage value v of the target temperature, a final temperature value T of the target temperature is generated.

[0014] This method can achieve real-time compensation through NTC chip reading circuit and compensation thermocouple, and cooperate with compensation algorithm, with stable accuracy within ±0.3℃, easy to operate and use, and low production cost.

[0015] In some possible implementations, the MCU circuit calculates the compensated thermocouple AD value V and further includes:

[0016] Smoothing is performed on the compensated measured thermocouple AD value V.

[0017] In some possible implementations, the compensated measured thermocouple AD value V is calculated using the following formula:

[0018] V=Vt+Voffset

[0019] Where V is the measured thermocouple AD value after compensation, Vt is the measured thermocouple AD value, and Voffset is the compensated thermocouple AD value.

[0020] In some possible implementations, generating the conversion voltage value vt includes:

[0021] Based on the thermocouple voltage-temperature conversion table, the temperature value Te of the NTC chip reading circuit is converted into a conversion voltage value vt.

[0022] In some possible implementations, the final temperature value T of the target temperature includes:

[0023] The voltage value v of the target temperature is converted into the final temperature value T of the target temperature based on the thermocouple voltage-temperature conversion table.

[0024] In some possible implementations, the voltage value v at the target temperature is generated using the following formula:

[0025] v=K×V+vt

[0026] Where v is the voltage value at the target temperature, K is the calibration coefficient, V is the measured thermocouple AD value after compensation, and vt is the converted voltage value vt.

[0027] In some possible implementations, the steps for calculating the calibration coefficient are:

[0028] Input a 4.096mV voltage at the interface of the thermocouple thermometer, and convert it into an AD value Vc of 4.096mV through the MCU circuit;

[0029] The calibration factor is calculated using the following formula:

[0030] K=4.096 / Vc

[0031] Where K is the calibration coefficient and Vc is the AD value of the 4.096mV voltage.

[0032] In a second aspect, a thermocouple thermometer is provided, which includes: a compensating thermocouple, a measuring thermocouple, a compensating measurement circuit, a target measurement circuit, an NTC chip reading circuit and an MCU circuit. The compensating thermocouple is connected to the compensating measurement circuit. The compensating thermocouple is used to measure the internal temperature of the thermocouple thermometer. The measuring thermocouple is connected to the target measurement circuit. The MCU circuit is respectively connected to the compensating measurement circuit, the target measurement circuit and the NTC chip reading circuit.

[0033] In some possible implementations, the compensation measurement circuit includes: a first interface end, a second bidirectional TVS tube, a fourth bidirectional TVS tube, a twenty-second capacitor, a twenty-first resistor, a first inductor and a twenty-third capacitor. The first interface end is connected to the compensation thermocouple, the second bidirectional TVS tube and the fourth bidirectional TVS tube are respectively connected to the first interface end, the first inductor is respectively connected to the second bidirectional TVS tube and the fourth bidirectional TVS tube, the first inductor is also connected to the MCU circuit, the twenty-second capacitor and the twenty-third capacitor are respectively connected to the two ends of the first inductor, and the twenty-first resistor is connected in parallel with the second bidirectional TVS tube.

[0034] In some possible implementations, the target measurement circuit includes: a second interface end, a first bidirectional TVS tube, a third bidirectional TVS tube, a nineteenth capacitor, a twentieth resistor, a second inductor, and a twentieth capacitor. The second interface end is connected to the measuring thermocouple, the first bidirectional TVS tube and the third bidirectional TVS tube are respectively connected to the second interface end, the second inductor is respectively connected to the first bidirectional TVS tube and the third bidirectional TVS tube, the second inductor is also connected to the MCU circuit, the nineteenth capacitor and the twentieth capacitor are respectively connected to both ends of the second inductor, and the twentieth resistor is connected in parallel with the first bidirectional TVS tube.

[0035] The present application is further described below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0037] Figure 1 1 is a flow chart of a cold junction compensation method for a thermocouple thermometer provided in an embodiment of the present application;

[0038] Figure 2 Schematic diagram of the structure of the thermocouple thermometer provided in the embodiment of the present application;

[0039] Figure 3 is a circuit diagram of a compensation measurement circuit provided in an embodiment of the present application;

[0040] Figure 4 is a circuit diagram of a target measurement circuit provided in an embodiment of the present application;

[0041] Figure 5 1 is a circuit diagram of an NTC chip reading circuit provided in an embodiment of the present application;

[0042] Figure 6 1 is a circuit diagram of the MCU circuit provided in an embodiment of the present application; DETAILED DESCRIPTION

[0043] To make the above-mentioned objects, features, and advantages of the present application more clearly understood, the specific embodiments of the present application are described in detail below with reference to the accompanying drawings. The following description sets forth many specific details to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the scope of the present application. Therefore, the present application is not limited to the specific embodiments disclosed below.

[0044] like Figures 2 to 6 As shown, this embodiment provides a thermocouple thermometer, which includes: a compensating thermocouple, a measuring thermocouple, a compensating measurement circuit, a target measurement circuit, an NTC chip reading circuit and an MCU circuit. The compensating thermocouple is connected to the compensating measurement circuit. The compensating thermocouple is used to measure the internal temperature of the thermocouple thermometer. The measuring thermocouple is connected to the target measurement circuit. The MCU circuit is respectively connected to the compensating measurement circuit, the target measurement circuit and the NTC chip reading circuit.

[0045] The MCU circuit is used to obtain the temperature value Te of the NTC chip reading circuit, measure the AD value Vt of the thermocouple, and compensate the AD value Voffset of the thermocouple.

[0046] like Figures 2 to 6 As shown, in some embodiments, the compensation measurement circuit includes: a first interface end, a second bidirectional TVS tube, a fourth bidirectional TVS tube, a twenty-second capacitor, a twenty-first resistor, a first inductor and a twenty-third capacitor. The first interface end is connected to the compensation thermocouple, the second bidirectional TVS tube and the fourth bidirectional TVS tube are respectively connected to the first interface end, the first inductor is respectively connected to the second bidirectional TVS tube and the fourth bidirectional TVS tube, the first inductor is also connected to the MCU circuit, the twenty-second capacitor and the twenty-third capacitor are respectively connected to the two ends of the first inductor, and the twenty-first resistor is connected in parallel with the second bidirectional TVS tube.

[0047] The first interface end is used to input the differential signal of the compensation thermocouple. The second bidirectional TVS tube and the fourth bidirectional TVS tube are used to suppress transient overvoltage and prevent excessive voltage from damaging subsequent circuits. The twenty-second capacitor is a differential mode filter capacitor, which is used to filter out differential mode high-frequency noise, bypass the high-frequency interference in the differential signal output by the compensation thermocouple, and retain the low-frequency differential mode signal. The twenty-first resistor cooperates with the second bidirectional TVS tube to limit the discharge current during overvoltage and avoid excessive current from damaging the circuit when the second bidirectional TVS tube is turned on. The twenty-third capacitor is a grounded filter capacitor, which forms a low-pass filter circuit with the first inductor to further filter out high-frequency noise and ensure that the signal input to the MCU circuit is a clean low-frequency differential voltage, meeting the signal quality requirements of the analog input module.

[0048] like Figures 2 to 6 As shown, in some embodiments, the target measurement circuit includes: a second interface end, a first bidirectional TVS tube, a third bidirectional TVS tube, a nineteenth capacitor, a twentieth resistor, a second inductor and a twentieth capacitor. The second interface end is connected to the measuring thermocouple, the first bidirectional TVS tube and the third bidirectional TVS tube are respectively connected to the second interface end, the second inductor is respectively connected to the first bidirectional TVS tube and the third bidirectional TVS tube, the second inductor is also connected to the MCU circuit, the nineteenth capacitor and the twentieth capacitor are respectively connected to the two ends of the second inductor, and the twentieth resistor is connected in parallel with the first bidirectional TVS tube.

[0049] The circuit structure and principle of the target measurement circuit are the same as those of the compensation measurement circuit, and are not described in detail here.

[0050] like Figure 1 As shown, this embodiment provides a cold-end compensation method for a thermocouple thermometer, which is applied to the thermocouple thermometer. The method includes steps S100 to S500.

[0051] Step S100: The MCU circuit obtains the temperature value Te of the NTC chip reading circuit, the AD value Vt of the measurement thermocouple, and the AD value Voffset of the compensation thermocouple;

[0052] In step S200, the MCU circuit calculates and compensates the thermocouple AD value V.

[0053] In this step, after the compensated measured thermocouple AD value V is calculated, the compensated measured thermocouple AD value V is smoothed.

[0054] In addition, the following formula is used to calculate the compensated measured thermocouple AD value V: V = Vt + Voffset

[0055] Where V is the measured thermocouple AD value after compensation, Vt is the measured thermocouple AD value, and Voffset is the compensated thermocouple AD value.

[0056] Step S300, generating a conversion voltage value vt according to the temperature value Te of the circuit read by the NTC chip;

[0057] Specifically, based on a thermocouple voltage-temperature conversion table, the temperature value Te of the NTC chip reading circuit is converted into a conversion voltage value vt. The thermocouple voltage-temperature conversion table is pre-set in the thermocouple thermometer.

[0058] Step S400 : generating a voltage value v of a target temperature according to the compensated measured thermocouple AD value V and the converted voltage value vt.

[0059] Specifically, the voltage value v of the target temperature is generated using the following formula: v = K × V + vt

[0060] Where v is the voltage value at the target temperature, K is the calibration coefficient, V is the measured thermocouple AD value after compensation, and vt is the converted voltage value vt.

[0061] The calculation steps of the calibration coefficient are:

[0062] Input a 4.096mV voltage at the interface of the thermocouple thermometer, and convert it into an AD value Vc of 4.096mV through the MCU circuit;

[0063] The calibration coefficient is calculated using the following formula: K = 4.096 / Vc

[0064] Where K is the calibration coefficient and Vc is the AD value of the 4.096mV voltage.

[0065] Step S500 : generating a final temperature value T of the target temperature according to the voltage value v of the target temperature.

[0066] Specifically, based on the thermocouple voltage-temperature conversion table, the voltage value v of the target temperature is converted into the final temperature value T of the target temperature.

[0067] This method can achieve real-time compensation through NTC chip reading circuit and compensation thermocouple, and cooperate with compensation algorithm, with stable accuracy within ±0.3℃, easy to operate and use, and low production cost.

[0068] The compensation method is verified by experimental data below. A thermocouple thermometer with LED lighting was used for verification. When the LED lighting function was turned on, the internal components of the thermometer heated up significantly, causing its internal temperature to rise from 25.8°C to 30.2°C within one hour, a change of 4.4°C. The changes in the target temperature measured by the thermometer within one hour were then recorded with and without the addition of a compensating thermocouple. Without the addition of a compensating thermocouple, the measured temperature increased from 25.8°C to 26.7°C, resulting in a measurement error of 0.9°C, as shown in Table (I) below. After the addition of the compensating thermocouple, the measured temperature changed from a maximum of 26.0°C to 25.7°C, stabilized after one hour, and the measurement error was within ±0.2°C, as shown in Table (II) below.

[0069] When no thermocouple compensation is added, the change of the measured target temperature within 1 hour is shown in Table (1):

[0070]

[0071]

[0072]

[0073]

[0074]

[0075] After adding the compensation thermocouple, the change of the measured target temperature within 1 hour is shown in Table (2):

[0076]

[0077]

[0078]

[0079]

[0080] It can be seen that after adding the compensation thermocouple, the accuracy of the change of the measured target temperature within 1 hour is within ±0.3℃, which effectively improves the measurement accuracy.

[0081] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0082] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of such features. Throughout the description of this application, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.

[0083] Any process or method description in a flowchart or otherwise described herein may be understood to represent a module, segment or portion of code comprising one or more executable instructions for implementing the steps of a custom logical function or process, and the scope of the preferred embodiments of the present application includes alternative implementations in which functions may be performed out of the order shown or discussed, including performing functions in a substantially simultaneous manner or in the reverse order depending on the functions involved, which should be understood by those skilled in the art to which the embodiments of the present application belong.

[0084] The logic and / or steps represented in the flowcharts or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing the logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (e.g., a computer-based system, a system including a processor, or other system that can fetch and execute instructions from an instruction execution system, apparatus, or device). For purposes of this specification, a "computer-readable medium" can be any device that can contain, store, communicate, propagate, or transport a program for use by, or in conjunction with, an instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of computer-readable media include the following: an electrical connection with one or more wires (electronic devices), a portable computer disk cartridge (magnetic device), random access memory (RAM), read-only memory (ROM), erasable and programmable read-only memory (EPROM or flash memory), fiber optic devices, and a portable compact disc read-only memory (CDROM). Furthermore, the computer-readable medium may even be paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium and then editing, interpreting or otherwise processing it in a suitable manner if necessary, and then storing it in a computer memory.

[0085] It should be understood that various parts of the present application can be implemented using hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented using software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented using hardware, as in another embodiment, any one of the following technologies known in the art or a combination thereof can be used to implement: a discrete logic circuit having a logic gate circuit for implementing a logic function on a data signal, an application-specific integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0086] Those skilled in the art will appreciate that all or part of the steps in the above-described method embodiments can be performed by instructing related hardware through a program. The program can be stored in a computer-readable storage medium, and when executed, the program includes one or a combination of the steps in the method embodiments. The aforementioned storage medium can be a read-only memory, a magnetic disk, or an optical disk.

[0087] In addition, the functional units in the various embodiments of the present application may be integrated into a processing module, or each unit may exist physically separately, or two or more units may be integrated into a module. The above-mentioned integrated module may be implemented in the form of hardware or in the form of a software functional module. If the integrated module is implemented in the form of a software functional module and sold or used as an independent product, it may also be stored in a computer-readable storage medium.

[0088] The above are merely preferred embodiments of the present application and do not constitute any form of limitation to the present application. Any person skilled in the art can, without departing from the scope of the technical solution of the present application, use the methods and technical contents disclosed above to make many possible changes and modifications to the technical solution of the present application, or modify it into an equivalent embodiment with equivalent changes. Therefore, all equivalent changes made based on the shape, structure and principle of the present application without departing from the content of the technical solution of the present application should be included in the scope of protection of the present application.

Claims

1. A cold junction compensation method for a thermocouple thermometer, applied to a thermocouple thermometer, characterized in that: The thermocouple thermometer includes: a compensating thermocouple, a measuring thermocouple, a compensating measurement circuit, a target measurement circuit, an NTC chip reading circuit and an MCU circuit, wherein the compensating thermocouple is connected to the compensating measurement circuit, the compensating thermocouple is used to measure the internal temperature of the thermocouple thermometer, the measuring thermocouple is connected to the target measurement circuit, and the MCU circuit is respectively connected to the compensating measurement circuit, the target measurement circuit and the NTC chip reading circuit; The method comprises: The MCU circuit obtains the temperature value Te of the NTC chip reading circuit, the AD value Vt of the measuring thermocouple, and the AD value Voffset of the compensation thermocouple; The MCU circuit calculates and compensates the measured thermocouple AD value V; Generate a conversion voltage value vt according to the temperature value Te of the circuit read by the NTC chip; Generate the voltage value v of the target temperature based on the compensated measured thermocouple AD value V and the converted voltage value vt; According to the voltage value v of the target temperature, a final temperature value T of the target temperature is generated.

2. The cold junction compensation method of thermocouple thermometer according to claim 1, characterized in that: The MCU circuit calculates and compensates the thermocouple AD value V, and further includes: The compensated measured thermocouple AD value V is smoothed.

3. The cold junction compensation method of thermocouple thermometer according to claim 1, characterized in that: The following formula is used to calculate the measured thermocouple AD value V after compensation: V=Vt+Voffset Where V is the measured thermocouple AD value after compensation, Vt is the measured thermocouple AD value, and Voffset is the compensated thermocouple AD value.

4. The cold junction compensation method of thermocouple thermometer according to claim 1, characterized in that: Generating the conversion voltage value vt includes: Based on the thermocouple voltage-temperature conversion table, the temperature value Te of the NTC chip reading circuit is converted into a conversion voltage value vt.

5. The cold junction compensation method of thermocouple thermometer according to claim 1, characterized in that: The final temperature value T of the target temperature includes: The voltage value v of the target temperature is converted into the final temperature value T of the target temperature based on the thermocouple voltage-temperature conversion table.

6. The cold junction compensation method of thermocouple thermometer according to claim 1, characterized in that: The voltage value v at the target temperature is generated using the following formula: v=K×V+vt Where v is the voltage value at the target temperature, K is the calibration coefficient, V is the measured thermocouple AD value after compensation, and vt is the converted voltage value vt.

7. The cold junction compensation method of thermocouple thermometer according to claim 6, characterized in that: The calculation steps of the calibration coefficient are: Input a 4.096mV voltage at the interface of the thermocouple thermometer, and convert the 4.096mV voltage into an AD value Vc through the MCU circuit; The calibration factor is calculated using the following formula: K=4.096 / Vc Where K is the calibration coefficient and Vc is the AD value of the 4.096mV voltage.

8. A thermocouple thermometer, characterized in that: The thermocouple thermometer includes: a compensating thermocouple, a measuring thermocouple, a compensating measurement circuit, a target measurement circuit, an NTC chip reading circuit and an MCU circuit. The compensating thermocouple is connected to the compensating measurement circuit. The compensating thermocouple is used to measure the internal temperature of the thermocouple thermometer. The measuring thermocouple is connected to the target measurement circuit. The MCU circuit is respectively connected to the compensating measurement circuit, the target measurement circuit and the NTC chip reading circuit.

9. The thermocouple thermometer according to claim 1, characterized in that: The compensation measurement circuit includes: a first interface end, a second bidirectional TVS tube, a fourth bidirectional TVS tube, a twenty-second capacitor, a twenty-first resistor, a first inductor, and a twenty-third capacitor. The first interface end is connected to the compensation thermocouple, the second bidirectional TVS tube and the fourth bidirectional TVS tube are respectively connected to the first interface end, the first inductor is respectively connected to the second bidirectional TVS tube and the fourth bidirectional TVS tube, the first inductor is also connected to the MCU circuit, the twenty-second capacitor and the twenty-third capacitor are respectively connected to both ends of the first inductor, and the twenty-first resistor is connected in parallel with the second bidirectional TVS tube.

10. The thermocouple thermometer according to claim 1, characterized in that: The target measurement circuit includes: a second interface end, a first bidirectional TVS tube, a third bidirectional TVS tube, a nineteenth capacitor, a twentieth resistor, a second inductor, and a twentieth capacitor. The second interface end is connected to the measurement thermocouple, the first bidirectional TVS tube and the third bidirectional TVS tube are respectively connected to the second interface end, the second inductor is respectively connected to the first bidirectional TVS tube and the third bidirectional TVS tube, the second inductor is also connected to the MCU circuit, the nineteenth capacitor and the twentieth capacitor are respectively connected to both ends of the second inductor, and the twentieth resistor is connected in parallel with the first bidirectional TVS tube.

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