An APL output temperature transmitter circuit integrated with a 2088 temperature measurement front end

Abstract

This invention discloses an APL output temperature transmitter circuit integrating a 2088 temperature sensing front-end. The 2088 temperature sensing front-end unit collects analog signals from an external temperature sensor, performs analog-to-digital conversion and algorithm processing, and then sends the temperature data and device status to a protocol conversion unit via a UART serial interface. The UART to APL protocol conversion unit encapsulates the data into APL Ethernet frames conforming to the 10BASE-T1L standard, converts them into differential signals through the physical layer, and outputs them to the field APL bus through the APL interface protection and matching unit. It also supports calibration and configuration commands issued from the APL bus side, which are transmitted transparently to the 2088 temperature sensing front-end unit via UART. The bus power supply management unit uses the DC power supply voltage input from the APL bus, which is converted and then uniformly powered by the power management unit. Compared with existing technologies, this invention achieves integrated design of the 2088 temperature sensing board and the APL conversion circuit, which can be built into a standard transmitter housing; it significantly shortens the R&D cycle, reduces costs, and enables the rapid launch of temperature transmitter products that meet the needs of industrial Ethernet upgrades.

Description

Technical Field

[0001] This invention belongs to the field of industrial automation instrumentation and industrial fieldbus technology, and particularly relates to an APL output temperature transmitter circuit with an integrated 2088 temperature measurement front end. Background Technology

[0002] In process industry sites, temperature is one of the most critical measurement parameters. The 2088 series intelligent temperature measuring board is a mature temperature measurement solution widely used in the industrial field. It supports multiple sensor inputs such as Pt100 / Pt1000 RTDs and S / K / E type thermocouples. It has a built-in 24-bit high-precision ADC and temperature measurement algorithm, and features temperature linearization, cold junction compensation, and fault self-diagnosis functions. The temperature measurement accuracy can reach ±0.1%FS. It typically provides 4-20mA+HART analog output and a local UART debugging interface.

[0003] APL (Advanced Physical Layer) is a new generation of process industry Ethernet physical layer specification based on the IEEE 802.3cg (10BASE-T1L) standard. It supports long-distance transmission of up to 1km with a single pair of twisted-pair cables, bus power supply and intrinsically safe explosion protection. It can be directly connected to industrial Ethernet DCS systems and is the core bus technology for the digital upgrade of process industries.

[0004] There are currently two main types of solutions for implementing APL output of temperature signals: ① Separate gateway solution: The 2088 temperature measuring board outputs a 4-20mA or HART signal, which is connected to an independent DIN rail-mounted APL gateway to convert the analog / bus signal into an APL Ethernet signal. ② Fully Customized Solution: Develop a brand-new temperature measurement motherboard from scratch, directly integrate the APL physical layer chip and protocol stack, and design a dedicated APL temperature transmitter unit.

[0005] The existing solutions have the following drawbacks and shortcomings: 1) Discrete gateway solutions have low integration and poor reliability: General APL gateways are rail-mounted, bulky, and cannot be built into the explosion-proof housing of standard temperature transmitters; additional connection cables from temperature measuring instruments to the gateway are required on site, resulting in many failure points and high wiring costs; moreover, most gateways only support one-way data acquisition and cannot be compatible with the original two-way interactive functions of the 2088 temperature measuring board, such as remote calibration, parameter configuration, and fault diagnosis, so the core functions of the temperature measuring board cannot be fully utilized.

[0006] 2) Fully customized solutions have high R&D costs and long cycles: Completely redesigning the APL temperature transmitter requires redeveloping the temperature measurement and conditioning circuit, calibration algorithm, and protocol stack, with an R&D cycle of 6 to 12 months; it also requires re-applying for metrological certification and explosion-proof certification, resulting in high investment costs and making it impossible to quickly adapt to market demands; at the same time, it is impossible to reuse the stability and algorithm resources of the 2088 series temperature measurement board that have been industrially verified over a long period of time.

[0007] 3) Insufficient interface compatibility and EMC performance: The existing general-purpose UART to APL module is not specifically adapted for the power and communication interfaces of the 2088 temperature measuring board, and the power and signal are not isolated and matched; the APL port protection circuit design is rudimentary and cannot meet the electromagnetic compatibility requirements of ±15kV ESD and surge impact in industrial sites, resulting in a high failure rate in harsh environments such as chemical and power plants. Summary of the Invention

[0008] The purpose of this invention is to provide an APL output temperature transmitter circuit that integrates a 2088 temperature measurement front end, realizing the integrated integration of the 2088 temperature measurement board and the APL conversion circuit, which can be built into a standard transmitter housing; significantly shortening the R&D cycle, reducing costs, and quickly launching temperature transmitter products that meet the industrial Ethernet upgrade requirements, thereby solving the problems mentioned in the background art.

[0009] To achieve the above objectives, the present invention provides the following technical solution: An APL output temperature transmitter circuit integrating a 2088 temperature measurement front-end includes a 2088 temperature measurement front-end unit, a UART to APL protocol conversion unit, an APL interface protection and matching unit, and a bus power supply management unit. The 2088 temperature measurement front-end unit acquires analog signals from an external temperature sensor, performs analog-to-digital conversion and algorithm processing, and then sends the temperature data and device status to the UART to APL protocol conversion unit via a UART serial interface. The UART to APL protocol conversion unit encapsulates the data into APL Ethernet frames conforming to the 10BASE-T1L standard, converts them into differential signals through the physical layer, and outputs them to the field APL bus through the APL interface protection and matching unit. It also supports calibration and configuration commands issued from the APL bus side, which are transmitted via UART to the 2088 temperature measurement front-end unit, achieving bidirectional full-function interaction. The bus power supply management unit uses the DC power supply voltage input from the APL bus, which is converted and then uniformly powered by the power management unit.

[0010] A further improvement to this invention is that the 2088 temperature sensing front-end unit uses the 2088 temperature sensing plate as the temperature sensing core and leads out four types of pins: The sensor input pin is connected to an external Pt100 / Pt1000 RTD or thermocouple, which is then connected to the on-site temperature measurement point.

[0011] The UART communication pins, including UART_TX, UART_RX, and GND, are full-duplex serial communication interfaces with a default baud rate of 9600bps, supporting temperature data upload and command issuance.

[0012] Power input pin, supports 3.3V DC power supply.

[0013] Functional pins are reserved for calibration and debugging interfaces.

[0014] A further improvement of the present invention is that the 2088 temperature measurement front-end unit has a built-in temperature measurement MCU and a 24-bit ADC, which can independently complete the entire process of signal conditioning, sampling, linearization compensation, and fault diagnosis, with a temperature measurement accuracy of ±0.1%FS and an operating temperature range of -40℃ to 85℃.

[0015] A further improvement to this invention is that the UART to APL protocol conversion unit is based on an industrial Ethernet control chip integrating the 10BASE-T1L physical layer, with peripheral configurations including reset, startup configuration, status indication, and communication interface circuits. The specific structure includes a control chip, reset and startup configuration circuits, and status indication circuits. Control chip: It has a built-in APL physical layer (PHY) and media access control layer (MAC), supports the IEEE 802.3cg10BASE-T1L standard, and is compatible with the APL bus specification; it also integrates multiple UART, GPIO, and SPI peripherals to realize protocol conversion and peripheral control.

[0016] The UART_RX pin of the control chip is connected to the UART_TX pin of the 2088 temperature measuring board, and the UART_TX pin is cross-connected with the UART_RX pin of the 2088 temperature measuring board. Both share a common ground (GND) to achieve full-duplex serial data pass-through.

[0017] The SPI interface (including pins such as SPI_MISO) is reserved for chip firmware upgrades and peripheral expansion.

[0018] Ethernet media interfaces such as ETH1_RX_N / ETH1_RX_P and ETH2_TX_N / ETH2_TX_P are brought out and finally converted into APL_P and APL_N differential bus signals.

[0019] Reset and startup configuration circuit: The RESET pin connects to the power-on reset RC circuit and the manual reset button to achieve automatic power-on reset and manual reset functions.

[0020] The BOOT pin is configured with pull-up and pull-down resistors to set the chip's boot mode to internal Flash boot, eliminating the need for an external memory chip.

[0021] The RESTORE_FACTORY pin is connected to a touch button. Pressing and holding the button for 5 seconds will trigger the factory reset function for on-site fault recovery.

[0022] Status indication circuit: The GPIO4 / 5 / 6 / 8 / 9 / 10 pins of the control chip drive multiple LED indicators respectively.

[0023] ETH_LED_SF1, ETH_LED_SF2: APL bus connection and speed status indicator lights, which stay on when the bus connection is successfully established.

[0024] ETH_LED_BF1, ETH_LED_BF2: APL bus data transceiver indicator lights, flashing during data transmission.

[0025] READY indicator light: stays on after the device initialization is complete, indicating the system running status.

[0026] Operation indicator light: flashes periodically during normal operation, and remains off or constantly lit during a fault.

[0027] A further improvement of the present invention is that the APL differential output and external bus terminal of the APL interface protection and matching unit are key circuits for ensuring EMC performance and signal integrity, and the specific structure is as follows: Differential ESD surge protection uses two differential signal lines, APL_P and APL_N, each connected in series with a TVS transient suppression diode. The cathode of the TVS transient suppression diode is connected to the differential signal line, and the anode is connected to the system protective ground. This TVS transient suppression diode can provide ±15kV contact discharge ESD protection and ±2kV surge suppression, while having low junction capacitance, which will not affect the quality of high-frequency differential signals.

[0028] The differential impedance matching network uses a 100Ω high-precision chip resistor in parallel between APL_P and APL_N to achieve differential characteristic impedance matching, eliminate signal reflection during long-distance transmission, and ensure signal integrity within a 1km transmission distance. At the same time, a small-value current-limiting resistor is connected in series, which, together with a TVS transient suppression diode, improves surge withstand capability.

[0029] The bus terminals, including APL_P and APL_N, are ultimately led out to the transmitter's two-wire terminals, directly connecting to the field APL bus cable, and simultaneously obtaining operating power through the bus.

[0030] A further improvement of the present invention is that the DC power supply management unit receives the DC power supply voltage from the APL bus, which passes through the reverse connection protection diode and the input filter circuit before entering the isolated DC-DC converter chip to output a stable 3.3V DC power supply, simultaneously powering the 2088 temperature measurement front-end unit and the UART to APL protocol conversion unit; the power supply circuit is equipped with an overcurrent protection fuse and multi-stage filter capacitors to meet the requirements of industrial-grade wide voltage input and intrinsically safe circuits.

[0031] A further improvement of the present invention is that the control chip is a 10BASE-T1LPHY industrial-grade chip.

[0032] A further improvement of the present invention is that the TVS transient suppression diode is model CDSOD323-T15SC.

[0033] The beneficial effects of this invention are: The APL output temperature transmitter circuit of the present invention, which integrates the 2088 temperature measurement front end, can directly reuse all the hardware, algorithms and certification resources of the mature 2088 series temperature measurement board, without the need to redevelop the temperature measurement circuit and calibration algorithm, shortening the R&D cycle by more than 70% and reducing the R&D cost by 60%; at the same time, it can be adapted to 2088 series temperature measurement boards with different ranges and different accuracy levels, and has strong product scalability.

[0034] The APL output temperature transmitter circuit of the present invention integrates the 2088 temperature measurement front end. All circuits can be built into the explosion-proof housing of a standard temperature transmitter. Compared with the separate solution of temperature measuring instrument + external gateway, the overall size is reduced by 75%, reducing field wiring and failure points. It supports two-wire bus power supply and is compatible with the installation and wiring methods of traditional transmitters, without the need to modify the field cable tray.

[0035] The APL output temperature transmitter circuit of the present invention, which integrates the 2088 temperature measurement front end, reduces the BOM cost by more than 30% compared with a fully customized APL temperature transmitter. At the same time, by reusing the mass production supply chain of mature temperature measurement boards, mass production can be achieved quickly, and the product launch cycle is significantly shortened. Attached Figure Description

[0036] Figure 1 This is a circuit schematic diagram of the UART to APL protocol conversion unit of the present invention.

[0037] Figure 2 , 3 4 and 5 are Figure 1 A magnified view of a portion of the image.

[0038] Figure 6 This is a schematic diagram of the structure of the APL interface protection and matching unit of the present invention.

[0039] Figure 7 ,8 9 is Figure 6 A magnified view of a portion of the image. Detailed Implementation

[0040] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments.

[0041] Example 1: This invention discloses an APL output temperature transmitter circuit integrating a 2088 temperature measurement front-end, including a 2088 temperature measurement front-end unit, a UART to APL protocol conversion unit, an APL interface protection and matching unit, and a bus power supply management unit. The 2088 temperature measurement front-end unit collects analog signals from an external temperature sensor, performs analog-to-digital conversion and algorithm processing, and then sends the temperature data and device status to the UART to APL protocol conversion unit via a UART serial interface. The UART to APL protocol conversion unit encapsulates the data into APL Ethernet frames conforming to the 10BASE-T1L standard, converts them into differential signals through the physical layer, and outputs them to the field APL bus through the APL interface protection and matching unit. It also supports calibration and configuration commands issued from the APL bus side, which are transmitted via UART to the 2088 temperature measurement front-end unit, achieving bidirectional full-function interaction. The bus power supply management unit uses the DC power supply voltage input from the APL bus, which is converted by the power management unit and then uniformly powered.

[0042] 2088 Temperature Measurement Front-End Unit:

[0043] This unit is a mature, general-purpose 2088 intelligent temperature measuring board for industrial applications. It supports Pt100 three-wire input, has a temperature measuring range of -200℃ to 600℃, a temperature measuring accuracy of ±0.1%FS, and a UART interface with a default baud rate of 9600bps. As the core of the temperature measuring system, it has four types of pins exposed to the outside.

[0044] Sensor input pins: Connect an external Pt100 / Pt1000 RTD or thermocouple to the field temperature measurement point.

[0045] UART communication pins: including UART_TX, UART_RX, and GND, is a full-duplex serial communication interface with a default baud rate of 9600bps, supporting temperature data upload and command issuance.

[0046] Power input pin: Supports 3.3V DC power supply.

[0047] Functional pins: Reserved for calibration and debugging interfaces.

[0048] This unit has a built-in temperature measurement MCU and a 24-bit ADC, which can independently complete the entire process of signal conditioning, sampling, linearization compensation, and fault diagnosis. The temperature measurement accuracy is ±0.1%FS, and the operating temperature range is -40℃ to 85℃.

[0049] UART to APL protocol conversion unit (corresponding principle) Figure 1-5 ):

[0050] This unit is the core conversion module of the invention. It is based on an industrial Ethernet control chip that integrates the 10BASE-T1L physical layer, and is equipped with reset, startup configuration, status indication, and communication interface circuits. The specific structure includes a control chip, a reset and startup configuration circuit, and a status indication circuit.

[0051] Control chip: It adopts an industrial-grade control chip with integrated 10BASE-T1LPHY, operates at 3.3V, and supports Class A intrinsically safe bus power supply. The control chip integrates the APL physical layer (PHY) and media access control layer (MAC), supports the IEEE 802.3cg10BASE-T1L standard, and is compatible with the APL bus specification; it also integrates multiple UART, GPIO, and SPI peripherals to realize protocol conversion and peripheral control.

[0052] The UART_RX pin of the control chip is connected to the UART_TX pin of the 2088 temperature measuring board, and the UART_TX pin is cross-connected with the UART_RX pin of the 2088 temperature measuring board. Both share a common ground (GND) to achieve full-duplex serial data pass-through.

[0053] An SPI interface (including pins such as SPI_MISO) is reserved for chip firmware upgrades and peripheral expansion.

[0054] Ethernet media interfaces such as ETH1_RX_N / ETH1_RX_P and ETH2_TX_N / ETH2_TX_P are brought out and finally converted into APL_P and APL_N differential bus signals.

[0055] Reset and startup configuration circuit: The RESET pin connects to the power-on reset RC circuit and the manual reset button to achieve automatic power-on reset and manual reset functions.

[0056] The BOOT pin is configured with pull-up and pull-down resistors to set the chip's boot mode to internal Flash boot, eliminating the need for an external memory chip.

[0057] The RESTORE_FACTORY pin is connected to a touch button. Pressing and holding the button for 5 seconds will trigger the factory reset function for on-site fault recovery.

[0058] Status indication circuit: The GPIO4 / 5 / 6 / 8 / 9 / 10 pins of the control chip drive multiple LED indicators respectively.

[0059] ETH_LED_SF1, ETH_LED_SF2: APL bus connection and speed status indicator lights, which stay on when the bus connection is successfully established.

[0060] ETH_LED_BF1, ETH_LED_BF2: APL bus data transceiver indicator lights, flashing during data transmission.

[0061] READY indicator light: stays on after the device initialization is complete, indicating the system running status.

[0062] Operation indicator light: flashes periodically during normal operation, and remains off or constantly lit during a fault.

[0063] APL Interface Protection and Matching Unit (Corresponding Principle) Figure 6-9 ):

[0064] This unit connects the APL differential output of the protocol conversion unit to the external bus terminal. It is a key circuit for ensuring EMC performance and signal integrity. The specific structure is as follows: Differential ESD surge protection: Two differential signal lines, APL_P and APL_N, are each connected in series with a CDSD323-T15SC type TVS transient voltage suppressor diode (principle). Figure 6-9 The device features a differential matching resistor with 1% accuracy (D2), a TVS transient suppression diode with its cathode connected to the differential signal line and its anode connected to the system protective ground. This device provides ±15kV contact discharge ESD protection and ±2kV surge suppression, while maintaining low junction capacitance to avoid affecting the quality of high-frequency differential signals.

[0065] Differential impedance matching network: A 100Ω high-precision chip resistor is connected in parallel between APL_P and APL_N to achieve differential characteristic impedance matching, eliminate signal reflection during long-distance transmission, and ensure signal integrity within a 1km transmission distance; at the same time, a small-value current-limiting resistor is connected in series, which, together with a TVS transient suppression diode, improves surge withstand capability.

[0066] Bus terminals: Finally, the APL_P and APL_N wires are led out to the two-wire terminals of the transmitter, which are directly connected to the field APL bus cable and obtain the working power through the bus.

[0067] Bus-powered power management unit: The APL bus input of the bus-fed power management unit receives a DC power supply voltage of 9V to 36V. After passing through the reverse polarity protection diode and the input filter circuit, the voltage enters the isolated DC-DC converter chip, which outputs a stable 3.3V DC power supply, simultaneously powering the 2088 temperature measurement front-end unit and the protocol conversion unit. The power circuit is equipped with an overcurrent protection fuse and multi-stage filter capacitors. The entire circuit can be integrated into a standard industrial temperature transmitter explosion-proof housing, with a protection rating of IP65, meeting the on-site installation requirements of chemical, power and other industries.

[0068] The specific working process of this invention is as follows: (1) Power-on initialization phase After the APL bus is connected, the bus power supply enters the power management unit, outputting a stable 3.3V power supply. The 2088 temperature measurement front-end unit and the protocol conversion unit are powered on simultaneously. The protocol conversion chip completes the startup according to the BOOT pin configuration, loads the APL protocol stack and UART driver, and lights up the READY indicator after initialization. The 2088 temperature measurement board simultaneously completes the temperature measurement circuit self-test and initialization.

[0069] (2) Temperature acquisition and data upload stage The 2088 temperature measurement front-end unit periodically collects signals from external temperature sensors. After ADC sampling, cold junction compensation, and linearization calculation, it generates a data frame containing temperature value, equipment status, and diagnostic information. This data frame is then sent to the UART to APL protocol conversion unit via the UART interface at fixed intervals.

[0070] Protocol conversion and bus output stage After receiving the UART data frame, the protocol conversion unit encapsulates it into an Ethernet frame according to the APL protocol specification, converts it into a 10BASE-T1L differential analog signal through the internal PHY, and outputs it to the APL bus through the interface protection and matching circuit, and then uploads it to the DCS or upper control system.

[0071] Downlink instruction processing stage When the APL bus side sends commands such as parameter configuration, range modification, zero-point calibration, and firmware upgrade, the protocol conversion unit parses the command format and transmits it to the 2088 temperature measurement front-end unit through the UART interface. After the temperature measurement unit performs the corresponding operation, it sends the response result and execution status back through the UART. The protocol conversion unit encapsulates the data and returns it to the host system via the APL bus, realizing fully bidirectional functional interaction.

[0072] Status monitoring and fault indication phase During equipment operation, the bus status light indicates the APL link status in real time, and the transmit / receive indicator light flashes as data is transmitted. If an abnormality such as temperature measurement failure or bus link failure occurs, the corresponding indicator light switches status, and a fault code is uploaded through the bus for easy on-site maintenance.

[0073] This invention uses the mature 2088 temperature measuring board as the core of temperature measurement. It cross-connects with the APL protocol conversion unit via a UART serial interface, achieving modular integration of temperature measurement and bus communication functions. APL bus adaptation can be completed without modifying the core circuitry of the 2088 board. Two CDSOD323-T15SC TVS transient suppression diodes are used to provide surge protection to ground on the APL_P and APL_N differential lines, respectively. Combined with 100Ω impedance matching resistors between the lines, this ensures signal integrity for transmission over a 1km long distance while meeting industrial-grade EMC protection requirements. The protocol conversion unit provides complete transparency for the UART data from the 2088 temperature measuring board. The device supports bidirectional transmission, enabling both uplink transmission of temperature data and status information, and downlink transmission of parameter configuration, calibration, and diagnostic commands, fully retaining all the original functions of the 2088 temperature sensor board. It utilizes a single-channel APL bus for simultaneous data transmission and power supply, with the power management unit outputting a unified 3.3V power supply to both the temperature sensor and conversion units, eliminating the need for external power supplies, simplifying field wiring, and adapting to two-wire transmitter installation specifications. Multiple LED indicators are extended via GPIO, covering three categories: device operating status, bus connection status, and data transmission / reception status. This allows for quick fault identification without external debugging tools, improving field maintainability.

[0074] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent transformations or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. An APL output temperature transmitter circuit integrating a 2088 temperature sensing front-end, characterized in that: It includes a 2088 temperature measurement front-end unit, a UART to APL protocol conversion unit, an APL interface protection and matching unit, and a bus power supply management unit; The 2088 temperature measurement front-end unit collects analog signals from external temperature sensors. After analog-to-digital conversion and algorithm processing, it sends the temperature data and device status to the UART to APL protocol conversion unit via a UART serial interface. The UART to APL protocol conversion unit encapsulates the data into APL Ethernet frames conforming to the 10BASE-T1L standard, converts them into differential signals through the physical layer, and outputs them to the field APL bus through the APL interface protection and matching unit. It also supports calibration and configuration commands issued from the APL bus side, which are transmitted to the 2088 temperature measurement front-end unit via UART, realizing bidirectional full-function interaction. The bus power supply management unit uses the DC power supply voltage input from the APL bus, which is converted by the power management unit and then uniformly powered.

2. The APL output temperature transmitter circuit integrating a 2088 temperature sensing front-end as described in claim 1, characterized in that, The 2088 temperature sensing front-end unit uses the 2088 temperature sensing plate as the temperature sensing core and leads out four types of pins: The sensor input pin is connected to an external Pt100 / Pt1000 resistance temperature detector or thermocouple, and then connected to the field temperature measurement point. The UART communication pins, including UART_TX, UART_RX, and GND, are full-duplex serial communication interfaces with a default baud rate of 9600bps, supporting temperature data upload and command issuance. Power input pin, supports 3.3V DC power supply; Functional pins are reserved for calibration and debugging interfaces.

3. The APL output temperature transmitter circuit integrating a 2088 temperature sensing front end as described in claim 2, characterized in that: The 2088 temperature measurement front-end unit has a built-in temperature measurement MCU and a 24-bit ADC, which can independently complete the entire process of signal conditioning, sampling, linearization compensation, and fault diagnosis. The temperature measurement accuracy is ±0.1%FS, and the operating temperature range is -40℃ to 85℃.

4. The APL output temperature transmitter circuit integrating a 2088 temperature sensing front-end as described in claim 2, characterized in that, The UART to APL protocol conversion unit is based on an industrial Ethernet control chip integrating the 10BASE-T1L physical layer, and is surrounded by reset, startup configuration, status indication, and communication interface circuits. The specific structure includes a control chip, reset and startup configuration circuits, and status indication circuits. Control chip: It has a built-in APL physical layer and media access control layer, supports the IEEE 802.3cg10BASE-T1L standard, and is compatible with the APL bus specification; it also integrates multiple UART, GPIO, and SPI peripherals to realize protocol conversion and peripheral control. The UART_RX pin of the control chip is connected to the UART_TX pin of the 2088 temperature measuring board, and the UART_TX pin is cross-connected with the UART_RX pin of the 2088 temperature measuring board. Both share a common GND ground to achieve full-duplex serial data pass-through. An SPI interface is reserved for chip firmware upgrades and peripheral expansion. Ethernet media interfaces such as ETH1_RX_N / ETH1_RX_P and ETH2_TX_N / ETH2_TX_P are brought out and finally converted into APL_P and APL_N differential bus signals; Reset and startup configuration circuit: The RESET pin is connected to the power-on reset RC circuit and the manual reset button to realize the functions of automatic power-on reset and manual reset on site. The BOOT pin is configured with pull-up and pull-down resistors to set the chip's boot mode to internal Flash boot, eliminating the need for an external memory chip. The RESTORE_FACTORY pin is connected to a touch button. Pressing and holding the button for 5 seconds will trigger the factory reset function for on-site fault recovery. Status indication circuit: The GPIO4 / 5 / 6 / 8 / 9 / 10 pins of the control chip drive multiple LED indicators respectively; ETH_LED_SF1, ETH_LED_SF2: APL bus connection and speed status indicator lights, which are constantly lit when the bus connection is successfully established; ETH_LED_BF1 and ETH_LED_BF2: APL bus data transceiver indicator lights, flashing during data transmission; READY indicator light: stays on after device initialization is complete, indicating the system's operating status; Operation indicator light: flashes periodically during normal operation, and remains off or constantly lit during a fault.

5. The APL output temperature transmitter circuit integrating a 2088 temperature sensing front-end as described in claim 2, characterized in that, The APL differential output and external bus terminal of the APL interface protection and matching unit are key circuits for ensuring EMC performance and signal integrity. The specific structure is as follows: Differential ESD surge protection: Two differential signal lines, APL_P and APL_N, are each connected in series with a TVS transient suppression diode. The cathode of the TVS transient suppression diode is connected to the differential signal line, and the anode is connected to the system protective ground. This TVS transient suppression diode can provide ±15kV contact discharge ESD protection and ±2kV surge suppression. At the same time, it has low junction capacitance and will not affect the quality of high-frequency differential signals. The differential impedance matching network uses a 100Ω high-precision chip resistor in parallel between APL_P and APL_N to achieve differential characteristic impedance matching, eliminate signal reflection during long-distance transmission, and ensure signal integrity within a 1km transmission distance. At the same time, a small-value current-limiting resistor is connected in series with a TVS transient suppression diode to improve surge withstand capability. The bus terminals, including APL_P and APL_N, are ultimately led out to the transmitter's two-wire terminals, directly connecting to the field APL bus cable, and simultaneously obtaining operating power through the bus.

6. The APL output temperature transmitter circuit integrating a 2088 temperature sensing front end as described in claim 4, characterized in that: The bus-fed power management unit receives DC power from the APL bus input. After passing through a reverse polarity protection diode and an input filter circuit, the power enters an isolated DC-DC converter chip, outputting a stable 3.3V DC power supply. This power supply simultaneously powers the 2088 temperature measurement front-end unit and the UART to APL protocol conversion unit. The power circuit is equipped with an overcurrent protection fuse and multi-stage filter capacitors to meet industrial-grade wide voltage input and intrinsically safe circuit requirements.

7. The APL output temperature transmitter circuit integrating a 2088 temperature sensing front end as described in claim 4, characterized in that: The control chip is a 10BASE-T1LPHY industrial-grade chip.

8. The APL output temperature transmitter circuit integrating a 2088 temperature sensing front end as described in claim 5, characterized in that: The TVS transient suppression diode is model CDSD323-T15SC.

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