Thermocouple acquisition circuit and thermocouple acquisition method

Abstract

The invention provides a thermocouple acquisition circuit and an acquisition method, the thermocouple acquisition circuit comprises a CPU circuit, a channel selection circuit and an ADC acquisition circuit, and the channel selection circuit comprises a selection switch chip and a plurality of optocoupler relays; the CPU circuit is used for sending the control instruction to the selection switch chip; the selection switch chip is used for controlling the plurality of optocoupler relays to be turned on in turn according to the control instruction; the plurality of optocoupler relays are used for transmitting thermocouple analog signals to the ADC acquisition circuit; and the ADC acquisition circuit is used for converting the thermocouple analog signal into a digital signal and transmitting the digital signal to the CPU circuit. According to the invention, a plurality of optocoupler relays are supported through the same hardware ADC acquisition circuit, acquisition of various types of thermocouples is supported through different calculation coefficients of the CPU circuit, multiplexing of one ADC acquisition circuit by multiple channels is realized, and the problems that the number of channels is large and the cost is high are solved.

Description

Technical Field

[0001] The present disclosure relates to the field of industrial control technology, and in particular to a thermocouple acquisition circuit and an acquisition method. Background Art

[0002] In the DCS control system (distributed control system) in the field of industrial control, temperature monitoring is an important link. The temperature data of equipment in various places is under constant monitoring, which is directly related to safe production. Thermocouples are widely used in thermal instruments, so the thermocouple temperature acquisition module occupies an important position. Thermocouples output analog signals, which are easily interfered with. At the same time, there are many devices on site, which require a large number of acquisition channels. Based on the above multiple requirements, the existing technology usually adopts the following methods for acquisition: (1) Through a single interface, different channels can be acquired in sequence, thereby realizing the multi-channel thermocouple acquisition function, which can realize multi-channel thermocouple acquisition with fewer resources and maximize resource utilization. This method belongs to the field of aviation electrical technology, focusing on collecting multiple thermocouple channels, which is quite different from the application environment in the field of industrial control; (2) By designing an open slot, the isothermal block is placed in the open slot of each thermocouple connector, and is tightly combined with the two conductive copper plates of each thermocouple connector through a thermally conductive silicone sheet, so that the thermocouple connector of each input channel is tightly combined through a thermally conductive silicone sheet, which avoids the inconsistency between the two electrodes of the thermocouple and the two poles of multiple thermocouples, ensuring the real-time and accuracy of the cold end compensation. At the same time, the isothermal block is also tightly combined with the internal temperature compensation circuit sensor of the thermocouple acquisition system on the PCB board (printed circuit board) through a thermally conductive silicone sheet, which improves the overall heat capacity of the cold end structure and reduces the temperature sensitivity of the cold end to the outside world. At the same time, the temperature board is a circuit board for installing the channel temperature sensor, and the thickness of the circuit board is a customized thickness, which can lift the channel temperature sensor close to the rear end of the conductive copper plate of the thermocouple connector, ensuring the accuracy of temperature measurement. This method mainly involves temperature compensation processing to improve the accuracy of temperature acquisition. It cannot meet the quantity and cost requirements in the field of industrial control; (3) Through a thermocouple and thermal resistor integrated acquisition card, including a solid-state relay connected to the thermocouple or thermal resistor; a control module connected to the solid-state relay; the control module controls the solid-state relay to switch the mode of thermocouple acquisition or thermal resistor acquisition. Multiple solid-state relays are configured, each connected to a thermocouple or thermal resistor; the control module polls the solid-state relay to make the channel between the selected solid-state relay and the thermocouple or thermal resistor conductive, and collect the analog value of the corresponding thermocouple or thermal resistor. This method is flexible in design and compatible with thermocouple and thermal resistor sensors in application scenarios, but it does not achieve the goal of one-to-many channels. Summary of the invention

[0003] The technical problem to be solved by the present disclosure is to overcome the defects of a large number of channels and high cost in the thermocouple acquisition method in the prior art, and to provide a thermocouple acquisition circuit and an acquisition method.

[0004] The present invention solves the above technical problems through the following technical solutions:

[0005] A first aspect of the present disclosure provides a thermocouple acquisition circuit, comprising a CPU circuit, a channel selection circuit and an ADC acquisition circuit, wherein the channel selection circuit comprises a selection switch chip and a plurality of optical coupler relays;

[0006] The CPU circuit is used to send control instructions to the selection switch chip;

[0007] The selection switch chip is used to control the multiple optical coupling relays to turn on in turn according to the control instruction;

[0008] The multiple photocoupler relays are used to transmit the thermocouple analog signal to the ADC acquisition circuit;

[0009] The ADC acquisition circuit is used to convert the thermocouple analog signal into a digital signal and transmit the digital signal to the CPU circuit.

[0010] Preferably, the thermocouple acquisition circuit further includes a post-stage isolation circuit;

[0011] The post-stage isolation circuit is used to isolate the multiple photocoupler relays from the CPU circuit.

[0012] Preferably, the thermocouple acquisition circuit further includes a channel front-stage protection circuit;

[0013] The channel front-stage protection circuit is used to filter and resist interference on the thermocouple acquisition circuit.

[0014] Preferably, the thermocouple acquisition circuit further includes a power supply circuit;

[0015] The power supply circuit is used to supply power to the thermocouple acquisition circuit.

[0016] Preferably, the thermocouple acquisition circuit further includes a temperature compensation circuit;

[0017] The temperature compensation circuit is used to perform temperature compensation on the collected external thermocouple device and transmit the temperature data to the CPU circuit.

[0018] Preferably, the thermocouple acquisition circuit further includes a post-stage isolation circuit;

[0019] The ADC acquisition circuit is used to convert the thermocouple analog signal into a digital signal, and transmit the digital signal to the CPU circuit through the post-stage isolation circuit.

[0020] Preferably, the channel front-stage protection circuit includes a thermocouple sensor access terminal and a filter combination component.

[0021] Preferably, the temperature compensation circuit includes an RTD acquisition circuit or a temperature sensor.

[0022] A second aspect of the present disclosure provides a thermocouple acquisition method, which is applicable to the thermocouple acquisition circuit described in the first aspect, and includes:

[0023] Sending control instructions to the selection switch chip through the CPU circuit;

[0024] Controlling multiple photocoupler relays to open in turn according to the control instruction through the selection switch chip;

[0025] The thermocouple analog signal is transmitted to the ADC acquisition circuit through the opened optical coupler relay;

[0026] The ADC acquisition circuit converts the thermocouple analog signal into a digital signal, and transmits the digital signal to the CPU circuit.

[0027] Preferably, the thermocouple acquisition method further comprises:

[0028] The CPU circuit converts the received digital signal into a corresponding numerical value, and transmits the numerical value to the host computer.

[0029] On the basis of being in accordance with the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present disclosure.

[0030] The positive and progressive effects of this disclosure are:

[0031] The present invention supports multiple optocoupler relays through the same hardware ADC acquisition circuit, supports various types of thermocouple acquisition through different calculation coefficients of the CPU circuit, realizes multi-channel multiplexing of one ADC acquisition circuit, and solves the problem of large number of channels and high cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A schematic diagram of a thermocouple acquisition circuit provided in Example 1 of the present disclosure;

[0033] Figure 2 A flow chart of a thermocouple acquisition method provided in Example 2 of the present disclosure. DETAILED DESCRIPTION

[0034] The present disclosure is further described below by way of examples, but the present disclosure is not limited to the scope of the examples.

[0035] Prefixes such as "first" and "second" are used in the embodiments of the present disclosure only to distinguish different description objects, and have no limiting effect on the position, order, priority, quantity or content of the described objects. The use of prefixes such as ordinal numbers to distinguish description objects in the embodiments of the present disclosure does not constitute a limitation on the described objects. For the statement of the described objects, please refer to the description in the context of the claims or embodiments, and no unnecessary limitation should be constituted due to the use of such prefixes. In addition, in the description of the present embodiment, unless otherwise specified, the meaning of "plurality" is two or more.

[0036] In the embodiments of the present disclosure, the collection, storage, use, processing, transmission, provision and disclosure of user personal information involved are in compliance with the provisions of relevant laws and regulations and do not violate public order and good morals.

[0037] Example 1

[0038] Figure 1 A schematic diagram of a thermocouple acquisition circuit provided in Example 1 of the present disclosure, such as Figure 1 As shown, it includes a CPU circuit 1, a channel selection circuit 2 and an ADC acquisition circuit 3. The channel selection circuit 2 includes a selection switch chip 21 and a plurality of optical coupler relays 22. It should be noted that an optical coupler relay has one TC channel, such as Figure 1 As shown, 8 optocoupler relays have 8 TC channels (for example, TC1, TC2, TC3, TC4, TC5, TC6, TC7, TC8)

[0039] CPU circuit 1, used for sending control instructions to the selection switch chip 21;

[0040] In this embodiment, the CPU circuit includes the chip MCU_GD32F450ZGT6 and FPGA_GW2A-18K.

[0041] In this embodiment, the CPU circuit uses FPGA_GW2A-18K chip, which sends configuration data information to each circuit to configure the chip working mode, and receives digital signals and transmits them to MCU_GD32F450ZGT6. MCU_GD32F450ZGT6 is responsible for running the collected data algorithm, converting the thermocouple analog signal into temperature value, and communicating with the host computer controller.

[0042] The selection switch chip 21 is used to control multiple optical coupler relays 22 to turn on in turn according to the control instruction;

[0043] A plurality of optical coupler relays 22, used for transmitting the thermocouple analog signal to the ADC acquisition circuit 3;

[0044] In this embodiment, the number of optocoupler relays is set according to actual conditions. For example, it can be 8 optocoupler relays, or it can be set to other numbers, which are not specifically limited here.

[0045] In this embodiment, for example, the channel selection circuit mainly includes a SN74LVC138 selection switch chip and eight APW214S optocoupler relays.

[0046] Specifically, the channel selection circuit mainly receives the control of FPGA_GW2A-18K; the G1 pin of the SN74LVC138 chip receives the enable signal, and operates the chip pins Y0~Y7 output according to the high and low levels of the 123 pins. The output pins are connected to 8 APW214S optocoupler relays respectively. Only one optocoupler relay is turned on at the same time, allowing the thermocouple voltage signal to pass through and enter the ADC acquisition circuit. The 8 APW214S optocoupler relays switch in turn to achieve the purpose of multi-channel acquisition, and another function of the optocoupler relay is to withstand 2KV high voltage, which helps to protect the back-end ADC acquisition circuit from high voltage damage.

[0047] The ADC acquisition circuit 3 is used to convert the thermocouple analog signal into a digital signal and transmit the digital signal to the CPU circuit 1.

[0048] In this embodiment, the ADC acquisition circuit includes a first-level filter design composed of resistors and capacitors, a 5V pull-up and pull-down circuit design, and an external reference power supply chip SGM4027A. The purpose of the first-level filter design is to help filter out some interference of the ADC acquisition circuit when acquiring thermocouple signals. The purpose of the 5V pull-up and pull-down circuit design is to ensure that the ADC acquisition circuit reads full scale when no data is collected. The power supply chip SGM4027A provides a high-precision voltage signal of 2.048V for the ADC acquisition circuit, which is connected to the 7-pin AIN3, ensuring the accuracy requirements of the ADC acquisition circuit in converting digital signals. The working principle of the ADC acquisition circuit: The 2-pin ALERT of the power supply chip SGM4027A sends a ready instruction to the FPGA_GW2A-18K, and receives configuration signals, including gain multiples, internal and external reference voltage selection, etc. The voltage analog signal is converted into a digital signal and transmitted to the isolation chip, and then sent to the CPU circuit.

[0049] It should be noted that the ADC acquisition circuit uses domestic ADC, and the domestic ADC can be SGM58200.

[0050] This embodiment supports multiple optocoupler relays through the same hardware ADC acquisition circuit, supports various types of thermocouple acquisition through different calculation coefficients of the CPU circuit, realizes multi-channel multiplexing of one ADC acquisition circuit, and solves the problem of large number of channels and high cost.

[0051] In an optional embodiment, if Figure 1 As shown, the thermocouple acquisition circuit also includes a post-stage isolation circuit 4;

[0052] The post-stage isolation circuit 4 is used to isolate the multiple optocoupler relays from the CPU circuit.

[0053] In this embodiment, the post-stage isolation circuit mainly utilizes the isolation chip NSI810XN-DSPR to isolate multiple optocoupler relays and the CPU circuit.

[0054] In an optional embodiment, the thermocouple acquisition circuit further includes a channel pre-stage protection circuit;

[0055] The channel pre-stage protection circuit is used to filter and resist interference for the thermocouple acquisition circuit.

[0056] In an optional embodiment, the channel front-stage protection circuit includes a thermocouple sensor access terminal and a filter combination component.

[0057] In an optional embodiment, if Figure 1 As shown, the thermocouple acquisition circuit also includes a power supply circuit 5;

[0058] The power supply circuit 5 is used to supply power to the thermocouple acquisition circuit.

[0059] In this embodiment, the power supply circuit mainly uses the domestic Jinshengyang module DC-DC 24V, that is, the power supply circuit mainly uses the URB2405S-6WR3 power module responsible for converting DC24V to 5V, and the SGM61022XTDE8G power module is responsible for converting DC5V to 3.3V. The above mainly involves the use of related chips such as CPU circuits. In addition, the power supply network is composed of B2412S, RS3007-5.0AYF, and RS3007-3.3AYF, and the 24V to 12V, 12V to 5V, and 5V to 3.3V power supply channels are used to isolate the front-end circuit.

[0060] In an optional embodiment, if Figure 1 As shown, the thermocouple acquisition circuit also includes a temperature compensation circuit 6;

[0061] The temperature compensation circuit 6 is used to perform temperature compensation on the collected external thermocouple device and transmit the temperature data to the CPU circuit.

[0062] In an optional embodiment, the temperature compensation circuit 6 includes an RTD acquisition circuit 61 or a temperature sensor 62 .

[0063] In this embodiment, there are two types of temperature compensation circuits. One is the RTD acquisition circuit, which requires an external three-wire PT100 sensor for signal acquisition and transmits it to the host computer for combined calculation with thermocouple data. Another design is to place the temperature sensor chip CT7117AJ4R near the terminal side, directly transmit the temperature data to the CPU circuit through the IIC protocol, and uniformly process it to obtain the actual temperature value.

[0064] In an optional embodiment, the thermocouple acquisition circuit further includes a post-stage isolation circuit;

[0065] The ADC acquisition circuit is used to convert the thermocouple analog signal into a digital signal and transmit the digital signal to the CPU circuit through a post-stage isolation circuit.

[0066] In the specific implementation process, the CPU circuit sends a configuration signal, opens the channel selection circuit, selects a thermocouple analog signal to enter the pins AIN0 and AIN1 of the ADC acquisition circuit through the optocoupler relay and the filter circuit, and at the same time, the ADC acquisition circuit selects the corresponding gain and reference source for conversion, and then transmits the digital signal to the CPU circuit through the isolation circuit; the temperature compensation circuit at the other end also transmits the corresponding digital signal to the CPU circuit, and the CPU circuit processes the collected data with a unified algorithm, and converts it into corresponding numerical values ​​through different calculation coefficients and displays them on the interface of the host computer 7 for the user to read.

[0067] Furthermore, this embodiment uses FPGA_GW2A-18K to control the SN74LVC138 chip to switch the APW214S channel. Through the ADC acquisition circuit, channel selection circuit, and external high-precision reference source design, the one thousandth accuracy requirement is achieved. Through the hardware circuit and software program to cooperate with analog quantity acquisition, the goal of multiplexing one ADC acquisition circuit is achieved. Redundancy is achieved through two temperature compensation methods to ensure the safety and reliability of the temperature acquisition function.

[0068] In the DCS control system, the present embodiment can achieve the same hardware ADC acquisition circuit to support multiple thermocouple temperature acquisitions, and support various types of thermocouple acquisitions through different calculation coefficients of the CPU circuit. Multiple channels can be switched to reuse one ADC acquisition circuit, saving a lot of hardware costs. The dual temperature compensation circuit provides redundant function guarantee for safe production. Specifically, two temperature compensation channel solutions are supported on one PCB board, which can be flexibly used according to user needs, solving the problem of a large number of TC channels and high module hardware cost in the DCS control system, meeting engineering application requirements, and being able to read temperature data transmitted by various types of thermocouples, with strong anti-interference ability.

[0069] Example 2

[0070] Corresponding to the aforementioned embodiment of a thermocouple acquisition circuit, the present disclosure also provides an embodiment of a thermocouple acquisition method.

[0071] Figure 2 This is a flow chart of a thermocouple acquisition method provided in Example 1 of the present disclosure. The thermocouple acquisition method is applicable to the thermocouple acquisition circuit described in Example 1. Figure 2 As shown, the thermocouple acquisition method includes:

[0072] S1, sending control instructions to the selection switch chip through the CPU circuit;

[0073] In this embodiment, the CPU circuit includes the chip MCU_GD32F450ZGT6 and FPGA_GW2A-18K.

[0074] In this embodiment, the CPU circuit uses FPGA_GW2A-18K chip, which sends configuration data information to each circuit to configure the chip working mode, and receives digital signals and transmits them to MCU_GD32F450ZGT6. MCU_GD32F450ZGT6 is responsible for running the collected data algorithm, converting the thermocouple analog signal into temperature value, and communicating with the host computer controller.

[0075] S2, through the selection switch chip according to the control instruction to control multiple optocoupler relays to open in turn;

[0076] S3, transmit the thermocouple analog signal to the ADC acquisition circuit through the opened optical coupler relay;

[0077] In this embodiment, the number of optocoupler relays is set according to actual conditions. For example, it can be 8 optocoupler relays, or it can be set to other numbers, which are not specifically limited here.

[0078] In this embodiment, for example, the channel selection circuit mainly includes a SN74LVC138 selection switch chip and eight APW214S optocoupler relays.

[0079] Specifically, the channel selection circuit mainly receives the control of FPGA_GW2A-18K; the G1 pin of the SN74LVC138 chip receives the enable signal, and operates the chip pins Y0~Y7 output according to the high and low levels of the 123 pins. The output pins are connected to 8 APW214S optocoupler relays respectively. Only one optocoupler relay is turned on at the same time, allowing the thermocouple voltage signal to pass through and enter the ADC acquisition circuit. The 8 APW214S optocoupler relays switch in turn to achieve the purpose of multi-channel acquisition, and another function of the optocoupler relay is to withstand 2KV high voltage, which helps to protect the back-end ADC acquisition circuit from high voltage damage.

[0080] S4. Convert the thermocouple analog signal into a digital signal through the ADC acquisition circuit, and transmit the digital signal to the CPU circuit.

[0081] In this embodiment, the ADC acquisition circuit includes a first-level filter design composed of resistors and capacitors, a 5V pull-up and pull-down circuit design, and an external reference power supply chip SGM4027A. The purpose of the first-level filter design is to help filter out some interference of the ADC acquisition circuit when acquiring thermocouple signals. The purpose of the 5V pull-up and pull-down circuit design is to ensure that the ADC acquisition circuit reads full scale when no data is collected. The power supply chip SGM4027A provides a high-precision voltage signal of 2.048V for the ADC acquisition circuit, which is connected to the 7-pin AIN3, ensuring the accuracy requirements of the ADC acquisition circuit in converting digital signals. The working principle of the ADC acquisition circuit: The 2-pin ALERT of the power supply chip SGM4027A sends a ready instruction to the FPGA_GW2A-18K, and receives configuration signals, including gain multiples, internal and external reference voltage selection, etc. The voltage analog signal is converted into a digital signal and transmitted to the isolation chip, and then sent to the CPU circuit.

[0082] It should be noted that the ADC acquisition circuit uses domestic ADC, and the domestic ADC can be SGM58200.

[0083] This embodiment supports multiple optocoupler relays through the same hardware ADC acquisition circuit, supports various types of thermocouple acquisition through different calculation coefficients of the CPU circuit, realizes multi-channel multiplexing of one ADC acquisition circuit, and solves the problem of large number of channels and high cost.

[0084] In an optional embodiment, the thermocouple acquisition method further includes:

[0085] The received digital signal is converted into a corresponding numerical value through the CPU circuit and the numerical value is transmitted to the host computer.

[0086] In the DCS control system, the present embodiment can achieve the same hardware ADC acquisition circuit to support multiple thermocouple temperature acquisitions, and support various types of thermocouple acquisitions through different calculation coefficients of the CPU circuit. Multiple channels can be switched to reuse one ADC acquisition circuit, saving a lot of hardware costs. The dual temperature compensation circuit provides redundant function guarantee for safe production. Specifically, two temperature compensation channel solutions are supported on one PCB board, which can be flexibly used according to user needs, solving the problem of a large number of TC channels and high module hardware cost in the DCS control system, meeting engineering application requirements, and being able to read temperature data transmitted by various types of thermocouples, with strong anti-interference ability.

[0087] As for the system embodiment, since it basically corresponds to the method embodiment, the relevant parts can refer to the partial description of the method embodiment. The system embodiment described above is only illustrative, wherein the units described as separate components may or may not be physically separated, and the components as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the disclosed solution.

[0088] Although the specific embodiments of the present disclosure are described above, those skilled in the art should understand that this is only an example, and the protection scope of the present disclosure is defined by the appended claims. Those skilled in the art may make various changes or modifications to these embodiments without departing from the principles and essence of the present disclosure, but these changes and modifications all fall within the protection scope of the present disclosure.

Claims

1. A thermocouple acquisition circuit, characterized in that: It includes a CPU circuit, a channel selection circuit and an ADC acquisition circuit, wherein the channel selection circuit includes a selection switch chip and a plurality of optical coupler relays; The CPU circuit is used to send control instructions to the selection switch chip; The selection switch chip is used to control the multiple optical coupling relays to turn on in turn according to the control instruction; The multiple photocoupler relays are used to transmit the thermocouple analog signal to the ADC acquisition circuit; The ADC acquisition circuit is used to convert the thermocouple analog signal into a digital signal and transmit the digital signal to the CPU circuit.

2. The thermocouple acquisition circuit according to claim 1, characterized in that: The thermocouple acquisition circuit also includes a post-stage isolation circuit; The post-stage isolation circuit is used to isolate the multiple photocoupler relays from the CPU circuit.

3. The thermocouple acquisition circuit according to claim 1, characterized in that: The thermocouple acquisition circuit also includes a channel front-stage protection circuit; The channel front-stage protection circuit is used to filter and resist interference on the thermocouple acquisition circuit.

4. The thermocouple acquisition circuit according to claim 1, characterized in that: The thermocouple acquisition circuit also includes a power supply circuit; The power supply circuit is used to supply power to the thermocouple acquisition circuit.

5. The thermocouple acquisition circuit according to claim 1, characterized in that: The thermocouple acquisition circuit also includes a temperature compensation circuit; The temperature compensation circuit is used to perform temperature compensation on the collected external thermocouple device and transmit the temperature data to the CPU circuit.

6. The thermocouple acquisition circuit according to claim 1, characterized in that: The thermocouple acquisition circuit also includes a post-stage isolation circuit; The ADC acquisition circuit is used to convert the thermocouple analog signal into a digital signal, and transmit the digital signal to the CPU circuit through the post-stage isolation circuit.

7. The thermocouple acquisition circuit as claimed in claim 3, characterized in that: The channel front-stage protection circuit includes a thermocouple sensor access terminal and a filter combination component.

8. The thermocouple acquisition circuit as claimed in claim 5, characterized in that: The temperature compensation circuit includes an RTD acquisition circuit or a temperature sensor.

9. A thermocouple collection method, characterized in that: The thermocouple acquisition method is applicable to the thermocouple acquisition circuits described in claims 1 to 8, and the thermocouple acquisition method comprises: Sending control instructions to the selection switch chip through the CPU circuit; Controlling multiple photocoupler relays to open in turn according to the control instruction through the selection switch chip; The thermocouple analog signal is transmitted to the ADC acquisition circuit through the opened optical coupler relay; The ADC acquisition circuit converts the thermocouple analog signal into a digital signal, and transmits the digital signal to the CPU circuit.

10. The thermocouple collection method according to claim 9, characterized in that: The thermocouple acquisition method also includes: The CPU circuit converts the received digital signal into a corresponding numerical value, and transmits the numerical value to the host computer.

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