A temperature measurement circuit and method based on a thermocouple sensor

Abstract

The application discloses a PLC temperature measurement circuit based on thermocouple sensors, comprising: a plurality of thermocouple sensors; a signal channel unit, which is provided with a plurality of paths in one-to-one correspondence with each thermocouple sensor, wherein each path of the signal channel unit adopts a combined low-pass filter circuit composed of a pi-type passive low-pass filter, an instrument amplifier, a first-order active low-pass filter and a second-order active Butterworth low-pass filter; a signal acquisition unit, which adopts a SAR-type ADC integrated circuit chip; and a signal processing unit, which further filters and processes received digital signals, and converts the processed digital signals into final required temperature values. The PLC temperature measurement circuit greatly improves the reliability of a PLC control system in temperature acquisition and control of automatic equipment.

Description

Technical Field

[0001] This invention relates to the field of PLC temperature measurement, and specifically to a circuit and implementation method for PLC temperature measurement based on a thermocouple sensor. Background Technology

[0002] A PLC (Programmable Logic Controller) is a microprocessor-based digital controller. Because it can automatically control external expansion components, it has important applications in the control systems of various types of equipment.

[0003] In the application of automated control of equipment, PLC temperature measurement based on thermocouple sensors is an indispensable and important application of PLC control systems in the field of automation control.

[0004] PLC temperature measurement based on thermocouple sensors often adopts the traditional technical solution with imported brand Σ-Δ type ADC integrated circuit chips as the core: the small voltage analog signal generated by the thermocouple sensor is processed by a simple low-pass filter circuit and then transmitted to the analog voltage input port of the ADC integrated circuit chip. The ADC integrated circuit chip converts the analog signal into a digital signal before further processing.

[0005] Traditional technical solutions suffer from the following drawbacks: simple low-pass filter circuits are insufficient to eliminate severe interference in complex electromagnetic environments, causing interference signals to superimpose on the tiny analog voltage signal generated by the thermocouple sensor, leading to temperature measurement deviations; the analog-to-digital conversion time within a Σ-Δ ADC integrated circuit chip is typically on the order of hundreds of milliseconds, and the polling acquisition cycle for multi-channel systems can reach hundreds of milliseconds or even seconds, resulting in temperature measurement lag. This inevitably affects the reliability of the PLC control system in acquiring and controlling the temperature of automated equipment. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a PLC temperature measurement circuit and its implementation method based on a thermocouple sensor. This temperature measurement circuit effectively eliminates interference signals aliased on the minute analog voltage signal generated by the thermocouple sensor, thus resolving the problem of temperature measurement deviation. The employed temperature measurement method effectively reduces the multi-channel polling acquisition cycle time, solving the problem of temperature measurement lag. This significantly improves the reliability of the PLC control system for temperature acquisition and control of automated equipment.

[0007] To achieve the above objectives, the present invention proposes the following technical solution:

[0008] A PLC temperature measurement circuit based on a thermocouple sensor includes:

[0009] Several thermocouple sensors;

[0010] The signal channel unit is equipped with several channels corresponding to each thermocouple sensor. Each signal channel unit transmits the small voltage analog signal generated by the corresponding thermocouple sensor to the signal acquisition unit. The signal channel unit adopts a combined low-pass filter circuit consisting of a π-type passive low-pass filter, an instrumentation amplifier, a first-order active low-pass filter, and a second-order active Butterworth low-pass filter to amplify and filter the received small voltage analog signal.

[0011] The signal acquisition unit includes an analog signal amplification / filtering circuit, which uses a SAR-type ADC integrated circuit chip to convert the received analog signal into a digital signal and transmit it to the signal processing unit.

[0012] The signal processing unit further filters the received digital signal and converts the processed digital signal into the final required temperature value.

[0013] The signal processing unit includes an MCU microprocessor chip and a digital signal communication interface.

[0014] The signal acquisition unit includes a SAR-type ADC integrated circuit chip, a digital signal communication interface, and an analog signal input interface;

[0015] Furthermore, the SAR-type ADC integrated circuit chip of the signal acquisition unit can be, but is not limited to, chips such as SGM51652 and ADS8688;

[0016] The signal channel unit includes an analog signal amplification / filtering circuit composed of operational amplifiers, resistors, capacitors, common-mode inductors, etc., an analog signal input interface, and an analog signal output interface;

[0017] Furthermore, the analog signal amplification / filtering circuit of the above signal channel unit includes operational amplifiers U1A, U1B, U2A, U2B, resistors R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13, R14, R15, R16, R17, R18, R19, capacitors C1, C2, C3, C4, C5, C6, C7, C8, C9, and common-mode inductor CM1;

[0018] Furthermore, the analog signal amplification / filtering circuit of the signal channel unit is a combined low-pass filter circuit consisting of a π-type passive low-pass filter, an instrumentation amplifier, a first-order active low-pass filter, and a second-order active Butterworth low-pass filter.

[0019] The digital signal communication interface of the aforementioned signal processing unit can be a conventional digital signal communication interface such as SPI, I2C, CAN, or USART built into the MCU microprocessor chip.

[0020] The digital signal communication interface of the signal acquisition unit can be a conventional digital signal communication interface such as SPI, I2C, CAN or USART built into the SAR-type ADC integrated circuit chip.

[0021] The digital signal communication interface of the signal processing unit is connected to the digital signal communication interface of the signal acquisition unit.

[0022] The analog signal input interface of the signal acquisition unit is connected to the analog signal output interface of the plurality of signal channel units;

[0023] The analog signal input interface of the signal channel unit is connected to the thermocouple sensor.

[0024] The thermocouple sensors mentioned above can be, but are not limited to, conventional K-type, J-type, T-type, or S-type thermocouple sensors.

[0025] The present invention also provides a method for performing temperature measurement using the above-mentioned PLC temperature measurement circuit, comprising the following steps:

[0026] S1. The tiny analog voltage signal generated by the thermocouple sensor is transmitted to the signal channel unit through the analog signal input interface of the signal channel unit. After being processed by the analog signal amplification / filtering circuit, it is transmitted to the analog signal output interface of the signal channel unit.

[0027] S2. The analog signal output interface of several signal channel units transmits several analog signals to the analog signal input interface of the signal acquisition unit. The SAR-type ADC integrated circuit chip in the signal acquisition unit sequentially polls and acquires the analog voltage signal of the analog signal input interface of the signal acquisition unit. After being processed internally by the SAR-type ADC integrated circuit chip, it is converted into a digital signal and transmitted to the digital signal communication interface of the signal acquisition unit.

[0028] S3, the digital signal communication interface of the signal acquisition unit transmits the digital signal to the digital signal communication interface of the signal processing unit. After receiving the digital signal, the MCU microprocessor chip of the signal processing unit can arbitrarily and flexibly configure a variety of digital filtering algorithms to further digitally filter the digital signal and convert the processed digital signal into the final required temperature value.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] This invention relates to a PLC temperature measurement circuit based on a thermocouple sensor, which improves upon the traditional ADC integrated circuit chip and low-pass filter circuit. The simple low-pass filter circuit is replaced with a combined low-pass filter circuit consisting of a π-type passive low-pass filter, an instrumentation amplifier, a first-order active low-pass filter, and a second-order active Butterworth low-pass filter. This effectively eliminates interference signals aliased on the small analog voltage signal generated by the thermocouple sensor, solving the problem of temperature measurement deviation. Furthermore, the Σ-Δ type ADC integrated circuit chip is replaced with a SAR type ADC integrated circuit chip. The time for converting analog signals to digital signals within the ADC integrated circuit chip is reduced from hundreds of milliseconds to several microseconds, effectively reducing the multi-channel polling acquisition cycle time and solving the problem of temperature measurement lag.

[0031] The PLC temperature measurement circuit based on thermocouple sensors of this invention can effectively improve the reliability of PLC control system for temperature acquisition and control of automated equipment.

[0032] It should be understood that all combinations of the foregoing concepts and the additional concepts described in more detail below can be considered part of the inventive subject matter of this disclosure, provided that such concepts do not contradict each other.

[0033] The foregoing and other aspects, embodiments, and features of the teachings of the present invention will be more fully understood from the following description in conjunction with the accompanying drawings. Other additional aspects of the invention, such as features and / or beneficial effects of exemplary embodiments, will become apparent from the following description or may be learned through practice of specific embodiments according to the teachings of the present invention. Attached Figure Description

[0034] The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component shown in the various figures may be denoted by the same reference numeral. For clarity, not every component is labeled in each figure. Embodiments of various aspects of the invention will now be described by way of example and with reference to the accompanying drawings, wherein:

[0035] Figure 1 This is a schematic diagram of the circuit structure for PLC temperature measurement based on a thermocouple sensor as described in this invention.

[0036] Figure 2 This is a schematic diagram of the signal channel unit described in this invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the described embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art.

[0038] The terms "first," "second," and similar words used in the specification and claims of this patent application do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, unless the context clearly indicates otherwise, the singular forms of "an," "a," or "the," etc., do not indicate a quantity limitation, but rather indicate the presence of at least one. Terms such as "comprising" or "including" indicate that the element or object preceding "comprising" encompasses the features, wholes, steps, operations, elements, and / or components listed following "comprising" or "including," and do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or collections thereof. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0039] This invention provides a circuit and implementation method for PLC temperature measurement based on a thermocouple sensor. The temperature measurement circuit effectively eliminates interference signals aliased on the small analog voltage signal generated by the thermocouple sensor, solving the problem of temperature measurement deviation. The temperature measurement method effectively reduces the multi-channel polling acquisition cycle time, solving the problem of temperature measurement lag. This significantly improves the reliability of the PLC control system for temperature acquisition and control of automated equipment. The invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0040] like Figure 1 As shown, a PLC temperature measurement circuit based on a thermocouple sensor includes a signal processing unit, a signal acquisition unit, and several signal channel units mounted on the signal acquisition unit.

[0041] The signal processing unit includes an MCU microprocessor chip and a digital signal communication interface;

[0042] The signal acquisition unit includes a SAR-type ADC integrated circuit chip, a digital signal communication interface, and an analog signal input interface;

[0043] Furthermore, the SAR-type ADC integrated circuit chip of the aforementioned signal acquisition unit can be, but is not limited to, chips such as SGM51652 and ADS8688;

[0044] The aforementioned signal channel unit includes an analog signal amplification / filtering circuit composed of operational amplifiers, resistors, capacitors, common-mode inductors, and other components, as well as an analog signal input interface and an analog signal output interface.

[0045] Furthermore, the analog signal amplification / filtering circuit of the signal channel unit includes operational amplifiers U1A, U1B, U2A, U2B, resistors R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13, R14, R15, R16, R17, R18, R19, capacitors C1, C2, C3, C4, C5, C6, C7, C8, C9, and common-mode inductor CM1;

[0046] Furthermore, the analog signal amplification / filtering circuit of the signal channel unit is a combined low-pass filter circuit consisting of a π-type passive low-pass filter, an instrumentation amplifier, a first-order active low-pass filter, and a second-order active Butterworth low-pass filter.

[0047] The digital signal communication interface of the signal processing unit can be a conventional digital signal communication interface such as SPI, I2C, CAN or USART built into the MCU microprocessor chip mentioned above.

[0048] The digital signal communication interface of the signal acquisition unit can be a conventional digital signal communication interface such as SPI, I2C, CAN or USART built into the SAR-type ADC integrated circuit chip mentioned above.

[0049] The digital signal communication interface of the signal processing unit is connected to the digital signal communication interface of the signal acquisition unit; the analog signal input interface of the signal acquisition unit is connected to the analog signal output interface of several signal channel units; the analog signal input interface of the signal channel units is connected to the thermocouple sensor.

[0050] Thermocouple sensors can be, but are not limited to, conventional K-type, J-type, T-type, or S-type thermocouple sensors.

[0051] In this embodiment, the analog signal amplification / filtering circuit of the signal channel unit is as follows: Figure 2 As shown, the system includes operational amplifiers U1A, U1B, U2A, and U2B; resistors R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13, R14, R15, R16, R17, R18, and R19; capacitors C1, C2, C3, C4, C5, C6, C7, C8, and C9; and a common-mode inductor CM1. Their connection relationship is as follows:

[0052] Pin 1 of common-mode inductor CM1 is connected to IN+ of the analog signal input interface; pin 2 of common-mode inductor CM1 is connected to IN- of the analog signal input interface; pin 3 of common-mode inductor CM1 is connected to one end of resistors R1 and R3; pin 4 of common-mode inductor CM1 is connected to one end of resistors R2 and R4; the other end of resistor R1 is connected to the power supply V-; the other end of resistor R2 is connected to the power supply V+; the other end of resistor R3 is connected to one end of resistor R5 and capacitor C1; the other end of resistor R4 is connected to one end of resistor R6 and capacitor C2; the other end of capacitors C1 and C2... One end of resistor R5 is connected to the power supply GND. The other end of resistor R5 is connected to one end of capacitor C3 and the non-inverting input of operational amplifier U1A. The other end of resistor R6 is connected to the other end of capacitor C3 and the non-inverting input of operational amplifier U1B. The inverting input of operational amplifier U1A is connected to one end of resistor R7 and one end of resistor R8. The inverting input of operational amplifier U1B is connected to the other end of resistor R7 and one end of resistor R9. The other end of resistor R8 is connected to one end of resistor R10. The other end of resistor R9 is connected to one end of resistor R11. The other end of resistor R10 is connected to the operational amplifier... The output terminal of amplifier U1A is connected to one end of resistor R12. The other end of resistor R11 is connected to the output terminal of operational amplifier U1B and one end of resistor R13. The other end of resistor R12 is connected to one end of resistor R14, one end of capacitor C4, and the non-inverting input terminal of operational amplifier U2A. The other end of resistor R13 is connected to one end of resistor R15, one end of capacitor C5, and the inverting input terminal of operational amplifier U2A. The other ends of resistor R14 and capacitor C4 are connected to power supply GND. The other end of resistor R15 and capacitor C5 are connected to the output terminal of operational amplifier U1B. One end of the signal channel unit is connected to one end of resistor R16. The other end of resistor R16 is connected to one end of resistor 18 and one end of capacitors C7, C8, and C9. The other end of resistor 18 is connected to one end of resistor R17. The other end of resistor R17 is connected to one end of capacitor C6 and the non-inverting input of operational amplifier U2B. The other end of capacitor C6 is connected to power supply GND. The inverting input of operational amplifier U2B is connected to one end of resistor R19. The other ends of capacitors C7, C8, and C9, the other end of resistor R19, and the output of operational amplifier U2B are connected to the OUT terminal of the analog signal output interface. In this embodiment, the number of signal channel units corresponds to the number of channels in the SAR-type ADC integrated circuit chip. As the number of SAR-type ADC integrated circuit chips increases, the number of signal channel units will also increase accordingly.

[0053] The following is in conjunction with the appendix Figure 1 The implementation method of the PLC temperature measurement circuit based on a thermocouple sensor disclosed in this invention will be further described in detail. The implementation method includes the following steps:

[0054] S1. The tiny analog voltage signal generated by the thermocouple sensor is transmitted to the signal channel unit through the analog signal input interface of the signal channel unit. After being processed by the analog signal amplification / filtering circuit, it is transmitted to the analog signal output interface of the signal channel unit.

[0055] S2. The analog signal output interface of several signal channel units transmits several analog signals to the analog signal input interface of the signal acquisition unit. The SAR-type ADC integrated circuit chip in the signal acquisition unit sequentially polls and acquires the analog voltage signal of the analog signal input interface of the signal acquisition unit. After being processed internally by the SAR-type ADC integrated circuit chip, it is converted into a digital signal and transmitted to the digital signal communication interface of the signal acquisition unit.

[0056] S3, the digital signal communication interface of the signal acquisition unit transmits the digital signal to the digital signal communication interface of the signal processing unit. After receiving the digital signal, the MCU microprocessor chip of the signal processing unit can arbitrarily and flexibly configure a variety of digital filtering algorithms to further digitally filter the digital signal and convert the processed digital signal into the final required temperature value.

[0057] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A PLC temperature measurement circuit based on a thermocouple sensor, characterized in that, include: Several thermocouple sensors; The signal channel unit is equipped with several channels corresponding to each thermocouple sensor. Each signal channel unit transmits the small voltage analog signal generated by the corresponding thermocouple sensor to the signal acquisition unit. The signal channel unit adopts a combined low-pass filter circuit consisting of a π-type passive low-pass filter, an instrumentation amplifier, a first-order active low-pass filter, and a second-order active Butterworth low-pass filter to amplify and filter the received small voltage analog signal. The signal acquisition unit includes an analog signal amplification / filtering circuit, which uses a SAR-type ADC integrated circuit chip to convert the received analog signal into a digital signal and transmit it to the signal processing unit. The signal processing unit further filters the received digital signal and converts the processed digital signal into the final required temperature value. The analog signal amplification / filtering circuit includes operational amplifiers U1A, U1B, U2A, and U2B; resistors R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13, R14, R15, R16, R17, R18, and R19; capacitors C1, C2, C3, C4, C5, C6, C7, C8, and C9; and a common-mode inductor CM1. The connections are as follows: pin 1 of common-mode inductor CM1 is connected to the IN+ pin of the analog signal input interface; pin 2 of common-mode inductor CM1 is connected to the IN- pin of the analog signal input interface; pin 3 of common-mode inductor CM1 is connected to one end of resistors R1 and R3; and the common-mode inductor... Pin 4 of CM1 is connected to one end of resistors R2 and R4. The other end of resistor R1 is connected to power supply V-, and the other end of resistor R2 is connected to power supply V+. The other end of resistor R3 is connected to one end of resistor R5 and capacitor C1. The other end of resistor R4 is connected to one end of resistor R6 and capacitor C2. The other ends of capacitors C1 and C2 are connected to power supply GND. The other end of resistor R5 is connected to one end of capacitor C3 and the non-inverting input of operational amplifier U1A. The other end of resistor R6 is connected to the other end of capacitor C3 and the non-inverting input of operational amplifier U1B. The inverting input of operational amplifier U1A is connected to one end of resistor R7 and resistor R8. The inverting input of operational amplifier U1B... The input terminal is connected to the other end of resistor R7 and one end of resistor R9. The other end of resistor R8 is connected to one end of resistor R10. The other end of resistor R9 is connected to one end of resistor R11. The other end of resistor R10 is connected to the output terminal of operational amplifier U1A and one end of resistor R12. The other end of resistor R11 is connected to the output terminal of operational amplifier U1B and one end of resistor R13. The other end of resistor R12 is connected to one end of resistor R14, one end of capacitor C4, and the non-inverting input terminal of operational amplifier U2A. The other end of resistor R13 is connected to one end of resistor R15, one end of capacitor C5, and the inverting input terminal of operational amplifier U2A. The other end of resistor R14 and the other end of capacitor C4... One end is connected to the power supply GND. The other end of resistor R15, the other end of capacitor C5, the output terminal of operational amplifier are connected to one end of resistor R16. The other end of resistor R16 is connected to one end of resistor 18, one end of capacitors C7, C8, and C9. The other end of resistor 18 is connected to one end of resistor R17. The other end of resistor R17 is connected to one end of capacitor C6 and the non-inverting input terminal of operational amplifier U2B. The other end of capacitor C6 is connected to the power supply GND. The inverting input terminal of operational amplifier U2B is connected to one end of resistor R19. The other ends of capacitors C7, C8, and C9, the other end of resistor R19, the output terminal of operational amplifier U2B are connected to the OUT of the analog signal output interface.

2. The PLC temperature measurement circuit according to claim 1, characterized in that, The capacitors C1 and C2 have the same parameters; the capacitors C4 and C5 have the same parameters; the capacitors C6, C7, C8, and C9 have the same parameters; the resistors R3 and R4 have the same parameters; the resistors R5 and R6 have the same parameters; the resistors R7, R8, R9, R10, and R11 have the same parameters; the resistors R12 and R13 have the same parameters; and the resistors R14 and R15 have the same parameters.

3. The PLC temperature measurement circuit according to claim 1 or 2, characterized in that, The signal processing unit includes an MCU microprocessor chip and a digital signal communication interface; the signal acquisition unit includes a digital signal communication interface, an analog signal input interface, and the SAR-type ADC integrated circuit chip; the signal channel unit includes an analog signal input interface, an analog signal output interface, and the analog signal amplification / filtering circuit; the digital signal communication interface of the signal processing unit is connected to the digital signal communication interface of the signal acquisition unit, and the analog signal input interface of the signal acquisition unit is connected to the analog signal output interface of each signal channel unit; the analog signal input interface of the signal channel unit is connected to the thermocouple sensor.

4. The PLC temperature measurement circuit according to claim 3, characterized in that, The SAR-type ADC integrated circuit chip uses SGM51652 or ADS8688; the digital signal communication interface of the signal acquisition unit uses the SPI, I2C, CAN or USART digital signal communication interface built into the SAR-type ADC integrated circuit chip; the digital signal communication interface of the signal processing unit uses the SPI, I2C, CAN or USART digital signal communication interface built into the MCU microprocessor chip; the thermocouple sensor uses K-type, J-type, T-type or S-type thermocouple sensor.

5. A measurement method using the PLC temperature measurement circuit of claim 3, characterized in that, Includes the following steps: S1. The tiny analog voltage signal generated by the thermocouple sensor is transmitted to the signal channel unit through the analog signal input interface of the signal channel unit. After being processed by the analog signal amplification / filtering circuit, it is transmitted to the analog signal output interface of the signal channel unit. S2. The analog signal output interface of several signal channel units transmits several analog signals to the analog signal input interface of the signal acquisition unit. The SAR-type ADC integrated circuit chip in the signal acquisition unit sequentially polls and acquires the analog voltage signal of the analog signal input interface of the signal acquisition unit. After being processed internally by the SAR-type ADC integrated circuit chip, it is converted into a digital signal and transmitted to the digital signal communication interface of the signal acquisition unit. S3. The digital signal communication interface of the signal acquisition unit transmits the digital signal to the digital signal communication interface of the signal processing unit. After receiving the digital signal, the MCU microprocessor chip of the signal processing unit further filters the digital signal through a digital filtering algorithm and converts the processed digital signal into the final required temperature value.

Images