An electronic device and a detection method for analog displacement sensor digitization

Abstract

The present application relates to displacement sensor signal conversion and industrial measurement field, concretely for a kind of electronic device and detection method for analog displacement sensor digitization.It includes signal sequentially connected overvoltage protection module, current voltage signal conversion module, analog-digital conversion module, single-chip microcomputer module and SSI output module;It also includes mode switching switch, shielding shell, analog signal acquisition board and SSI digital signal generation board, the mode switching switch is electrically connected with the control end of the current voltage signal conversion module, for switching between voltage input mode and current input mode.The beneficial effects of the present application are to solve the technical problems that the prior art has a single adaptation scenario, poor universality, high hardware cost, and cannot meet the needs of low-cost, large-scale and standardized transformation of 10,000 analog displacement sensors.

Description

Technical Field

[0001] This invention relates to the field of displacement sensor signal conversion and industrial measurement technology, and in particular to an electronic device that can accurately convert the voltage and current analog signals output by an analog displacement sensor into standard synchronous serial interface (SSI) digital signals, as well as a displacement detection method based on the device. It can be widely used in digital upgrade scenarios that require high-precision displacement measurement, such as aerospace ground strength testing, industrial automation measurement, structural health monitoring, and displacement detection of engineering machinery. Background Technology

[0003] Displacement sensors are one of the core fundamental sensors in the field of airborne ground strength testing. Their measurement accuracy, transmission stability, and anti-interference capabilities directly determine the performance ceiling of the entire measurement system and the test results.

[0004] In recent years, with the deepening of global industrial digital and intelligent transformation, digital displacement sensors have achieved rapid popularization and large-scale application in the field of industrial measurement due to their core advantages such as strong anti-electromagnetic interference capability, no signal attenuation over long distances, high measurement accuracy, ability to transmit absolute position data, and easy networking and integration with host computer measurement systems.

[0005] Among them, the Synchronous Serial Interface (SSI) is the mainstream standard interface for absolute displacement measurement devices in the industrial field. It has outstanding features such as unified timing specifications, strong interface compatibility, high transmission rate, and good synchronization. It has become the standard access interface for newly built and upgraded digital measurement systems in the industry. Most mainstream industrial measurement controllers and data acquisition devices use the SSI interface as the core access standard for displacement sensors.

[0006] Driven by this industry trend, the aviation strength testing system has also undergone a comprehensive digital upgrade, gradually initiating the digital iteration of the measurement system. It has procured and implemented digital displacement sensors compatible with SSI interfaces in bulk, marking the beginning of a high-precision, digital, and network-enabled upgrade of the measurement system. However, in the process of system upgrade implementation and daily production and operation, the applicant faces the dual core challenges of ensuring compatibility with existing equipment and adapting to new equipment. Firstly, the applicant has a huge stock of analog displacement sensors, mainly voltage and current analog displacement measurement products. The devices themselves still have good measurement performance and a compliant service life. If they are all replaced with brand new digital sensors due to the digital upgrade of the measurement system, it will result in a huge equipment replacement cost of tens of millions of yuan, causing serious waste of fixed assets. At the same time, large-scale equipment replacement and recalibration will lead to long-term shutdown of the production line, seriously affecting the normal production and operation order and causing unpredictable losses. Secondly, in the subsequent production operation, project implementation, equipment maintenance and spare parts turnover process, based on the adaptation requirements of special working conditions, the cost control of purchasing a single piece of equipment, the digestion of existing spare parts inventory and other factors, the applicant will continue to purchase and use some analog displacement sensors. However, the upgraded SSI interface digital measurement system cannot directly connect to the analog signal output by the analog displacement sensor, which makes the newly added analog sensor incompatible with the existing digital measurement system, which seriously restricts the flexible adaptation capability of the measurement system and the flexibility of equipment selection. Based on the aforementioned practical application scenarios, there is an urgent need for a solution that can accurately, stably, and with low latency convert the analog signals output by analog displacement sensors into standard SSI digital signals, achieving seamless compatibility between existing analog displacement sensors, newly added analog sensors, and existing SSI interface digital measurement systems. This solution must complete the digital adaptation of analog sensors without requiring large-scale replacement of existing sensor equipment or secondary modifications to the existing measurement system, while also considering industrial-grade measurement accuracy, strong anti-interference performance, low modification costs, and feasibility for mass deployment. Regarding the technology for converting analog signals to digital signals, there are currently some general-purpose technical solutions and commercial products in the industry. However, based on the applicant's comprehensive patent search, market research, and actual working condition verification, there is still no mature dedicated solution specifically adapted to industrial analog displacement sensors that can directly output standard SSI interface signals. Existing implementations that are most similar in function to this invention all have obvious technical defects and application limitations, and cannot meet the applicant's actual usage needs. The specific classification is as follows: A general-purpose analog signal acquisition and conversion module; this type of solution is the most mainstream commercial analog-to-digital conversion product on the market, and it is also the existing technology with the closest function to this invention. Its core capability is the acquisition and digital conversion of standard analog signals such as 4-20mA and ±10V. However, the core design goal of this type of solution is general-purpose industrial analog signal acquisition, rather than dedicated SSI signal conversion for analog displacement sensors, resulting in a fatal compatibility flaw.

[0007] On the one hand, the output protocols of these modules are mainly asynchronous industrial bus protocols such as RS485, Modbus-RTU, Ethernet, and Profinet, without specific timing and protocol designs for SSI synchronous serial interfaces. Therefore, their output asynchronous serial signals cannot be directly connected to digital measurement systems that use SSI synchronous serial interfaces as the standard. To achieve compatibility, additional protocol conversion gateways and secondary programming adaptation on the host computer are required. This not only significantly increases system complexity and the cost of modifying a single device, but the additional protocol conversion steps also introduce problems such as signal transmission delay, data packet loss, and timing mismatch, failing to meet the real-time, synchronous, and reliable requirements of precision displacement measurement.

[0008] On the other hand, these general-purpose modules are not specifically optimized for the signal characteristics of analog displacement sensors, lack front-end conditioning circuits adapted to weak differential signals, and lack core designs such as linearization calibration, temperature drift compensation, and multi-stage noise filtering. In the complex electromagnetic environment and wide temperature conditions of industrial sites, the signal conversion accuracy is severely lost, and it cannot meet the accuracy standards of industrial precision displacement measurement.

[0009] A simplified analog-to-digital (A / D) conversion circuit solution; existing simplified A / D conversion circuit solutions that are only publicly available in a scattered manner only realize the basic function of converting analog signals to digital signals. They are the existing technologies that are most similar to the underlying hardware logic of this invention, but they lack complete industrial-grade product design and dedicated adaptation capabilities.

[0010] This type of solution does not follow the international specifications of the standard SSI interface, lacks core designs such as synchronous clock matching, standard frame format encapsulation, and data verification, and the output digital signal has no unified timing and protocol standard. It cannot achieve plug-and-play compatibility with mainstream SSI interface measurement controllers and acquisition devices on the market, has extremely poor universality, and is completely unfeasible for large-scale retrofitting of existing equipment.

[0011] Encoder-specific signal conversion solutions: There are a few existing customized conversion solutions for rotary encoders that can convert incremental encoder pulse signals to SSI digital signals. These are the only similar solutions in the current technology that can output standard SSI signals. However, the input signal type and core processing logic of these solutions are completely different from the present invention. Their design for encoder pulse counting signals cannot be adapted to the continuously changing analog signals output by analog displacement sensors. Neither the hardware circuits nor the software algorithms can be directly transferred to the signal conversion scenarios of analog displacement sensors. At the same time, these customized solutions generally suffer from high hardware costs, large size, and limited adaptability. The cost of modifying a single unit far exceeds the value of the analog displacement sensor itself, making it uneconomical for large-scale equipment modification of tens of thousands of units.

[0012] In summary, there is currently no mature and dedicated solution in the existing technology specifically for industrial analog displacement sensors that can achieve accurate and stable conversion of analog signals to standard SSI digital signals. Existing similar solutions all suffer from core defects such as interface incompatibility, insufficient conversion accuracy, poor anti-interference performance, weak adaptability to working conditions, and high transformation costs. They cannot solve the problem of seamless compatibility between existing and newly added analog displacement sensors and SSI interface digital measurement systems during the digital upgrade of industrial measurement systems, and there is a significant technological gap. This is the core technical problem that this invention aims to solve. Summary of the Invention

[0013] This invention addresses the technical problems existing in the prior art by providing an electronic device and detection method for digitizing analog displacement sensors, aiming to solve the following core technical issues: Addressing the core pain point of interface compatibility in digital measurement systems: Existing digital measurement systems generally use the SSI synchronous serial interface as the standard access specification for displacement measurement devices, which cannot directly receive and parse the continuous analog signals output by analog displacement sensors. This results in existing analog displacement sensors not being able to be seamlessly reused with the existing system, and new analog sensors not being able to be adapted for access, causing asset waste and poor system adaptability. Addressing the timing and protocol deficiencies of existing solutions: Existing general analog-to-digital solutions only support asynchronous communication protocols such as RS485 and Modbus, lacking synchronous timing and frame format adaptation designs for standard SSI interfaces, making them unsuitable for plug-and-play use with mainstream SSI interface measurement devices; additional protocol conversion steps introduce problems such as transmission delay, timing mismatch, poor synchronization of multi-channel data, and increased system complexity, failing to meet the real-time and synchronization requirements of precision displacement measurement; To address the issues of insufficient measurement accuracy and operational stability: Existing simple A / D conversion circuits and general acquisition modules have not been specifically optimized for the signal characteristics of analog displacement sensors. They lack dedicated front-end signal conditioning, linearization calibration, temperature drift compensation, and multi-stage anti-interference design, resulting in signal conversion accuracy loss, data distortion, and insufficient operational stability under complex electromagnetic environments and wide temperature conditions in industrial settings, thus failing to guarantee the measurement accuracy of the original sensors. Addressing the issues of adaptability and cost-effectiveness in large-scale applications: Existing similar solutions have limited applicability to specific scenarios, poor versatility, and high hardware costs. They cannot simultaneously support voltage-type and current-type analog displacement sensors, and the cost of retrofitting a single unit is too high, failing to meet the needs of low-cost, large-scale, and standardized retrofitting of tens of thousands of existing analog displacement sensors.

[0014] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: An electronic device for digitizing an analog displacement sensor includes an overvoltage protection module, a current-to-voltage signal conversion module, an analog-to-digital conversion module, a microcontroller module, and an SSI output module connected in sequence; it also includes a mode switching switch, a shielded housing, an analog signal acquisition board, and an SSI digital signal generation board. The mode switching switch is electrically connected to the control terminal of the current-to-voltage signal conversion module and is used to switch between a voltage input mode and a current input mode. The overvoltage protection module serves as the signal input terminal of the device, used to receive the analog signal output by the analog displacement sensor and suppress transient overvoltages; the current-to-voltage signal conversion module converts a 4-20mA current signal into a 0-10V voltage signal in current input mode, and directly conducts the 0-10V voltage signal in voltage input mode; the analog-to-digital conversion module converts the analog voltage signal into a parallel digital signal and transmits it to the microcontroller module; the microcontroller module calibrates the digital signal and generates serial data conforming to the SSI protocol specification; the SSI output module converts the serial data into a standard differential SSI signal and outputs it to an external data acquisition device; The analog signal acquisition board and the SSI digital signal generation board are arranged in layers inside the shielded shell, with a metal shielding layer in between. The overvoltage protection module and the current-voltage signal conversion module are integrated into the analog signal acquisition board. The analog-to-digital conversion module, the microcontroller module, and the SSI output module are integrated into the SSI digital signal generation board. The shielded shell is made of aluminum alloy with a conductive anodized surface and an electromagnetic shielding effectiveness of ≥60dB. One end of the shielded shell has an analog signal female connector, the other end has an SSI signal male connector, a mode switching switch is located on the side, and fixing bolts are located at the bottom.

[0015] A detection method for digitizing an analog displacement sensor, the detection method specifically includes the following steps: Step 1: Working mode selection: According to the output type of the analog displacement sensor to be connected, toggle the mode switch to the corresponding position and select voltage input mode or current input mode; Step 2: Wiring the analog displacement sensor; Connect the signal output terminal of the analog displacement sensor to the analog signal female connector of the electronic device through a shielded cable, confirming that the wiring polarity is correct, the connection is secure, and the shielding layer is reliably grounded at one end. Step 3: Wiring the digital acquisition system; Connect the SSI signal male connector of the electronic device to the SSI standard interface of the data acquisition system through the dedicated SSI shielded cable, and confirm that the cable termination resistance is matched and the connection is secure; Step 4: System power-on and parameter configuration; sequentially connect the power supplies to the analog displacement sensor, electronic device and data acquisition system, configure the SSI interface parameters on the data acquisition system, and complete device identification and communication establishment; Step 5: System calibration and accuracy verification; Perform zero-point calibration and full-scale calibration on the electronic device. After calibration, input a standard displacement signal to verify the accuracy, linearity, and stability of the output data, and confirm that it meets the measurement requirements. Step 6; Formal Test and Data Acquisition; Start the test process. The data acquisition system synchronously reads the displacement data of each channel through the SSI interface, monitors the displacement changes in real time, and records the data of the entire test process. Step 7: End of test and equipment removal; After the test is completed, first disconnect the power supply to the data acquisition system and electronic devices, then disconnect the SSI side cables and analog sensor side cables in sequence, and organize and store the equipment.

[0016] The beneficial effects of this invention are: 1) The detection device of the present invention solves the technical problem that existing digital measurement systems generally use SSI synchronous serial interface as the standard access specification for displacement measurement equipment, which cannot directly receive and parse the continuous analog signals output by analog displacement sensors. This results in existing analog displacement sensors not being able to be seamlessly reused with the existing system and new analog sensors not being able to be adapted for access. Furthermore, it solves the technical problems that existing general analog-to-digital solutions only support asynchronous communication protocols such as RS485 and Modbus, lack synchronous timing and frame format adaptation design for standard SSI interfaces, cannot be plugged and played with mainstream SSI interface measurement equipment, and introduce transmission delay, timing mismatch, poor data synchronization, and increased system complexity through additional protocol conversion.

[0017] 2) The detection method of this invention solves the problems of insufficient measurement accuracy and working condition stability. It addresses the technical problems of existing simple A / D conversion circuits and general acquisition modules not being specifically optimized for the signal characteristics of analog displacement sensors, lacking dedicated front-end signal conditioning, linearization calibration, temperature drift compensation, and multi-stage anti-interference design, which leads to signal conversion accuracy loss, data distortion, and insufficient operational stability under complex industrial conditions. Furthermore, it solves the technical problems of existing similar solutions having limited applicability to specific scenarios, poor versatility, and high hardware costs, which cannot meet the needs of low-cost, large-scale, and standardized retrofitting of tens of thousands of existing analog displacement sensors.

[0018] Based on the above technical solution, the present invention can be further improved as follows.

[0019] Furthermore, the overvoltage protection module includes a transient suppression diode and a current-limiting resistor. The transient suppression diode is connected in parallel between the signal input path and ground, with a response time of less than 1ps and a breakdown voltage covering a range of 0-30V, and is used to absorb surge voltage and electrostatic pulses in industrial environments.

[0020] Furthermore, the current-voltage signal conversion module includes a sampling unit, an input filtering unit, a range calibration unit, and a differential amplification unit; The sampling unit includes a high-precision low-temperature drift sampling resistor with a resistance of 500Ω, an accuracy class of ±0.01%, a temperature coefficient of ≤5ppm / ℃, a rated power of ≥300mW, and is connected to the signal circuit using a four-wire connection method. The input filtering unit is an RC low-pass filter, consisting of a 100Ω precision resistor and a 0.1μF ceramic capacitor, with a cutoff frequency of approximately 15.9kHz, used to suppress high-frequency electromagnetic interference. The range calibration unit includes a zero-adjustment potentiometer and a full-scale potentiometer. The zero-adjustment potentiometer has a resistance of 10kΩ and is used to calibrate the zero-point parameter corresponding to 0V output for a 4mA input. The full-scale potentiometer has a resistance of 100kΩ and is used to calibrate the full-scale parameter corresponding to 10V output for a 20mA input. The differential amplifier unit uses an instrumentation amplifier with a common-mode rejection ratio ≥100dB to amplify the differential voltage across the sampling resistor to the 0-10V standard range.

[0021] Furthermore, the differential amplifier unit adopts Texas Instruments OPA series instrumentation amplifiers with an input offset voltage of less than 10μV, an offset voltage temperature drift of less than 0.1μV / ℃, a gain error of less than 0.01%, and a gain temperature drift of less than 1ppm / ℃.

[0022] Furthermore, the analog-to-digital conversion module adopts a 24-bit ΔΣ type analog-to-digital converter, supports four-channel synchronous sampling, has a maximum sampling rate of 128kSPS, and an effective resolution of 20.6 bits at a sampling rate of 8kSPS. It has a built-in programmable gain amplifier and digital filter, and supports communication with the microcontroller module via an SPI interface.

[0023] Furthermore, the microcontroller module adopts a 32-bit microcontroller with built-in Flash memory and RAM memory, and operates at a main frequency of not less than 72MHz. The microcontroller module has built-in sampling control unit, data calibration unit, and timing generation unit. The sampling control unit is used to configure the sampling rate, gain, and channel parameters of the analog-to-digital conversion module. The data calibration unit has built-in linear calibration algorithm, temperature drift compensation algorithm, and digital filtering algorithm to correct signal conversion errors. The timing generation unit is used to generate synchronous clocks and data frame timings that conform to the SSI international standard.

[0024] Furthermore, the SSI output module includes an RS-485 transceiver chip, supports a maximum transmission rate of 10Mbps, and outputs differential levels that conform to the SSI interface electrical specifications. The SSI signal frame output by the SSI output module includes a start bit, data bits, parity bits, and stop bits. The data bit length is configurable from 16 to 32 bits, and the parity mode supports switching between odd parity, even parity, and no parity, making it compatible with mainstream industrial SSI interface data acquisition devices.

[0025] Furthermore, in step 1, when the current input mode is selected, the mode switching switch connects the signal paths of the sampling unit and the differential amplifier unit, and the 4-20mA current signal is converted into a voltage signal and then output; when the voltage input mode is selected, the mode switching switch bypasses the sampling unit and the differential amplifier unit, and the 0-10V voltage signal is directly input to the analog-to-digital converter module after filtering.

[0026] The SSI interface parameter configuration in step 4 specifically includes setting the SSI clock frequency to 100kHz-2MHz, setting the data bit length to 24 bits, setting the parity method to odd parity, and setting the data encoding format to binary encoding. After the configuration is completed, the data acquisition system actively sends a clock synchronization signal, and the electronic device returns the device identification data, thus completing the handshake connection.

[0027] The specific procedures for zero-point calibration and full-scale calibration in step 5 are as follows: Step 501: Zero-point calibration; Place the analog displacement sensor at the zero-displacement reference position. After the signal stabilizes, trigger the zero-point calibration command at the data acquisition system. The electronic device records the current ADC sampling value and stores it as the zero-point reference value. Step 502: Full-scale calibration; Place the analog displacement sensor at the full-scale displacement reference position. After the signal stabilizes, trigger the full-scale calibration command. The electronic device records the current ADC sampling value and stores it as the full-scale reference value. Step 503: Linear Fitting; The microcontroller module establishes a linear mapping relationship between the ADC sampled value and the actual displacement value based on the zero-point reference value and the full-scale reference value, and completes the basic range calibration.

[0028] Furthermore, step 5 also includes multi-point linear calibration, specifically, at least 5 calibration points are uniformly selected within the measurement range, the standard displacement signal corresponding to each point is input sequentially, the ADC sampling value and standard displacement value of each calibration point are recorded, a high-order linear correction curve is obtained by fitting using the least squares method, and stored in the non-volatile memory of the microcontroller module to correct nonlinear errors within the entire measurement range.

[0029] Furthermore, in step 6, the data acquisition system uses an SSI synchronization clock to achieve synchronous acquisition of multiple electronic devices with a synchronization error of less than 1μs. The microcontroller module performs moving average filtering and outlier removal on the sampled data, and the data update rate supports up to 8kHz. The total signal transmission delay is less than 1ms. Attached Figure Description

[0030] Figure 1 This is a circuit block diagram of the electronic device of the present invention; Figure 2 This is a side view of the electronic device of the present invention. Figure 3 This is a top view of the electronic device of the present invention.

[0031] The attached diagram lists the components represented by each number as follows: 1. SSI signal male connector; 2. SSI digital signal generation board (PCB1); 3. Shielding housing; 4. Signal cable; 5. Mode switch; 6. Fixing bolts; 7. Analog signal acquisition board (PCB2); 8. Analog signal female connector; 101. Overvoltage protection module; 102. Current-voltage signal conversion module; 103. Analog-to-digital conversion module; 104. Microcontroller module; 105. SSI output module; 106. Analog displacement sensor; 107. Data acquisition equipment. Detailed Implementation

[0032] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0033] The present invention provides the following preferred embodiments. Example 1: like Figure 1-3 As shown, an electronic device for digitizing an analog displacement sensor is provided in this embodiment. The circuit part of the electronic device consists of an overvoltage protection module 101, a current-voltage signal conversion module 102, an analog-to-digital conversion module 103, a microcontroller module 104, and an SSI output module 105 connected in series. It can convert the analog signal output by the analog displacement sensor 106 into a standard SSI digital signal and connect it to the data acquisition device 107. The specific circuit design and working principle of each module are described in detail below. Overvoltage protection module 101; The overvoltage protection module 101 is located at the very front of the device's signal input and serves as the first line of defense against electrical interference in industrial environments. Industrial environments are prone to transient overvoltages generated by inductive load starts and stops, electrostatic discharge, and lightning strikes, with amplitudes reaching hundreds of volts. If these voltages directly enter subsequent precision circuits, they can cause permanent damage to components. This module utilizes a transient voltage suppressor diode (TVS) and a current-limiting resistor to form a protective circuit. The TVS diode is connected in parallel between the signal input line and signal ground. A bidirectional TVS device is selected, with a breakdown voltage set at 30V, slightly higher than the device's maximum input voltage (10V). This ensures that normal signal transmission is not affected while effectively suppressing overvoltages. When a transient high voltage occurs at the input, the TVS diode rapidly breaks down and conducts within picoseconds, clamping the voltage within a safe range and dissipating surge energy. A current-limiting resistor is connected in series in the signal path to limit the magnitude of the surge current and further protect the subsequent circuits. The response time of this module is less than 1ps and can withstand a peak surge current of up to 100A. The electrostatic discharge protection level meets the ±15kV air discharge requirements of the IEC 61000-4-2 standard, which can fully ensure the electrical safety of the subsequent precision analog circuits. Current-to-voltage signal conversion module 102; The current-to-voltage signal conversion module 102 is the core signal conditioning unit of the device, responsible for converting current signals to voltage signals, signal filtering, range calibration, and signal amplification. Its performance directly determines the conversion accuracy of the entire device. This module consists of four parts: a sampling unit, an input filtering unit, a range calibration unit, and a differential amplification unit. It also supports switching the operating mode via the mode switching switch 5. Sampling unit; The core function of the sampling unit is to convert a 4-20mA current signal into a voltage signal. The core component is a high-precision, low-temperature-drift sampling resistor. According to Ohm's law, current flowing through a resistor will generate a corresponding voltage drop. To convert a 20mA full-scale current into a voltage suitable for subsequent circuits, this design uses a 500Ω sampling resistor. A 20mA current flowing through it generates a 10V voltage drop, perfectly matching the 0-10V standard range. To ensure sampling accuracy, a high-precision metal foil resistor is used, with an accuracy class of ±0.01%, a temperature coefficient ≤5ppm / ℃, and a rated power of [missing information]. With a power rating ≥300mW, conventional carbon film resistors have an accuracy of only ±1% and a temperature drift of hundreds of ppm / ℃, which cannot meet the requirements for precision measurement. The sampling resistor selected in this design has an extremely low temperature drift; within an industrial temperature range of -40℃ to +85℃, the resistance change is less than 0.06%, significantly reducing measurement errors caused by temperature variations. Simultaneously, the sampling resistor uses a four-wire (Kelvin) connection: two wires are current paths, flowing through the 4-20mA current output by the sensor; the other two wires are voltage sampling lines, directly connected to the two ends of the sampling resistor and then to the subsequent amplifier circuit. The four-wire connection completely eliminates measurement errors caused by lead resistance, because almost no current flows through the voltage sampling lines, and the voltage drop on the leads is negligible, ensuring that the sampled voltage is exactly equal to the true voltage across the sampling resistor. This design is particularly important for long-distance transmission scenarios, avoiding additional errors introduced by temperature changes in cable resistance. Input filtering unit; Electromagnetic interference in industrial environments can couple onto signal cables, creating high-frequency noise that is superimposed on the effective displacement signal, causing fluctuations in measurement data. To suppress high-frequency interference, this module is designed with an RC low-pass filter, consisting of a 100Ω precision resistor and a 0.1μF multilayer ceramic capacitor. The calculated cutoff frequency of this RC filter is: fc = 1 / (2πRC) = 1 / (2×π×100×0.1×10^-6) ≈ 15.9kHz; The cutoff frequency design balances noise suppression and signal response speed: displacement signals are low-frequency, slowly varying signals, typically with a bandwidth not exceeding 1kHz, and a cutoff frequency of 15.9kHz will not attenuate the effective displacement signal; simultaneously, it can effectively suppress high-frequency electromagnetic interference above 10kHz commonly found in industrial environments, such as switching power supply noise and motor brush spark interference. Low-temperature coefficient NPO ceramic capacitors are selected to ensure minimal change in filtering characteristics with temperature. In voltage input mode, the input voltage signal directly passes through this RC filter unit before entering the subsequent circuit, eliminating the need for sampling and amplification stages, simplifying the signal path and reducing error sources. Range calibration unit; Due to manufacturing tolerances in components, the sampling resistor value and amplifier gain cannot be exactly equal to the theoretical values, leading to zero-point offset and full-scale error. Therefore, this module is designed with a range calibration unit, including a zero-adjustment circuit and a full-scale adjustment circuit, to correct system errors. The zero-adjustment circuit uses a 10kΩ multi-turn precision potentiometer to introduce a small compensation voltage to the amplifier input terminal through voltage division, which is used to offset the zero-point offset voltage of the circuit. The calibration method is as follows: apply a 4mA standard current (corresponding to zero displacement) to the input terminal, adjust the zero-adjustment potentiometer until the amplifier output voltage is exactly 0V, and complete the zero-point calibration. The full-scale adjustment circuit uses a 100kΩ multi-turn precision potentiometer to fine-tune the closed-loop gain of the amplifier and correct the full-scale error. The calibration method is as follows: apply a 20mA standard current (corresponding to full-scale displacement) to the input terminal, adjust the full-scale adjustment potentiometer until the amplifier output voltage is exactly 10V, and complete the full-scale calibration. The adjustment resolution of the multi-turn precision potentiometer is extremely high, which can achieve fine adjustment at the millivolt level to ensure calibration accuracy. The calibration parameters are calibrated at the hardware level and are fixed after calibration, so they are not affected by the microcontroller program and have higher reliability. Differential amplifier unit; The voltage across the sampling resistor is a differential signal with a relatively small amplitude (2V at 4mA and 10V at 20mA). It needs to be amplified and converted to single-ended signal by a differential amplifier while suppressing common-mode interference. This unit uses Texas Instruments' OPA series instrumentation amplifier, which is designed for precision industrial measurement and has an extremely high common-mode rejection ratio (CMRR≥100dB). It can effectively suppress common-mode electromagnetic interference on the signal line. Its input offset voltage is less than 10μV, offset voltage temperature drift is less than 0.1μV / ℃, gain error is less than 0.01%, and gain temperature drift is less than 1ppm / ℃. It has excellent overall performance and will not introduce significant additional errors. The amplifier gain is precisely set by an external resistor, converting the 0-10V differential voltage across the sampling resistor into a 0-10V single-ended voltage output. At the same time, impedance transformation is achieved, reducing the output impedance, improving the load-driving capacity, and ensuring the accuracy of sampling by the subsequent ADC. Analog-to-digital conversion module 103; The function of the analog-to-digital converter module 103 is to convert continuously changing analog voltage signals into discrete digital signals. It is a bridge connecting the analog world and the digital world. Its resolution and linearity directly determine the upper limit of the measurement accuracy of the device. This design selects the TI ADS131A04 24-bit ΔΣ analog-to-digital converter. This chip is designed for industrial precision measurement and has the following core characteristics. High resolution and high precision: Adopting a ΔΣ oversampling architecture with a built-in digital filter, the effective resolution reaches 20.6 bits at a sampling rate of 8kSPS. For the full scale of 0-10V, the minimum resolution is approximately 10V / 2^20.6 ≈ 6.6μV, which is much higher than the 10mV resolution corresponding to a 0.1% accuracy sensor, ensuring that the measurement accuracy of the sensor is not compromised at all. The typical chip integral nonlinearity (INL) is ±3ppm, guaranteeing excellent linearity across the entire scale. Synchronous sampling: Supports four-channel synchronous sampling. Although this device uses a single channel, the synchronous sampling architecture ensures that the sampling time is accurate and controllable, which is convenient for multiple devices to work synchronously. Programmable gain: Built-in programmable gain amplifier (PGA) supports gain switching from 1 to 128 times, which can adapt to input signals of different amplitudes and improve the accuracy of small signal measurement; Low power consumption and industrial-grade temperature range: Operating temperature range -40℃ to +125℃, meeting the requirements of industrial applications; The ADC chip is connected to the microcontroller module 104 via the SPI interface. The microcontroller configures the ADC's sampling rate, gain, channels, and other parameters via the SPI bus and reads the converted digital sampled values. After the ADC conversion is completed, it sends an interrupt signal to the microcontroller via the DRDY pin to notify the microcontroller to read the data, ensuring the real-time performance of data reading. The oversampling and noise shaping characteristics of the ΔΣ type ADC itself have extremely strong anti-interference capabilities, which can push high-frequency noise outside the signal bandwidth and then filter it out by a digital filter. Compared with the traditional SAR type ADC, it is more suitable for the noise environment of industrial sites. 104 microcontroller module; The microcontroller module 104 is the core of the control and data processing of the entire device. It uses an STM32F1 series 32-bit ARM Cortex-M3 microcontroller with a main frequency of 72MHz. It has 128KB Flash memory and 20KB RAM memory, which are sufficient in resources, low in cost, industrial-grade temperature range, and high reliability. The internal functions of the microcontroller module can be divided into three core units: sampling control unit, data calibration unit and timing generation unit. Sampling control unit; The sampling control unit is responsible for configuring the operating parameters of the ADC chip and reading the ADC sampling data according to a fixed timing sequence. After the microcontroller powers on, it first writes the configuration register to the ADC via the SPI interface, setting parameters such as the sampling rate to 8kSPS, gain to 1x, enabling the internal reference voltage, and enabling the digital filter. After configuration, the ADC begins continuous conversion. After each conversion, an external interrupt is triggered on the microcontroller. In the interrupt service routine, the microcontroller reads the 24-bit sampling data and stores it in the data buffer. This unit is also responsible for monitoring the ADC's operating status. If a communication abnormality or data error occurs, it will automatically reset the ADC and reconfigure it to ensure the reliability of the system operation. Data calibration unit; The raw ADC sample values ​​contain hardware system errors, temperature drift errors, and random noise, which need to be corrected using digital algorithms to obtain accurate displacement values. The data calibration unit has three built-in algorithms; Linear calibration algorithm: Based on the zero-point reference value and full-scale reference value obtained from calibration, a linear mapping formula between the ADC sampled code value and the actual displacement value is established. Actual displacement = (sampled code value - zero-point code value) / (full-scale code value - zero-point code value) × full-scale displacement value. For multi-point calibration scenarios, the least squares method is used to fit the second-order correction curve to correct the nonlinear error between the ADC and the front-end circuit, and further improve the full-scale linearity. Temperature drift compensation algorithm: The microcontroller has a built-in temperature sensor that can monitor the internal temperature of the chip in real time. Based on a pre-calibrated temperature drift coefficient, the sampled values ​​are compensated for to offset the zero-point drift and gain drift caused by temperature changes, thereby improving measurement accuracy in a wide temperature range. Digital filtering algorithm: A composite filtering algorithm combining moving average filtering and median filtering is used to process continuously sampled data. This algorithm can filter out random high-frequency noise and suppress sudden pulse interference, outputting smooth and stable displacement data. The filtering depth is configurable, allowing users to adjust it according to their needs for response speed and smoothness. The calibration parameters are stored in the microcontroller's internal Flash memory and are not lost when power is off, allowing for long-term use after a single calibration. A calibration command interface is also provided, supporting on-site recalibration via the SSI bus or a dedicated calibration interface. SSI timing generation unit; The SSI interface is a synchronous serial interface. The master device (data acquisition system) provides the synchronization clock, and the slave device (this device) outputs data bit by bit under clock drive. The timing generation unit's function is to serially output the calibrated displacement data according to the standard SSI frame format, synchronized with an external clock. The standard SSI frame structure includes: a start bit (1 bit, active low), data bits (N bits, displacement data, high-order bit first), a parity bit (1 bit, optional), and a stop bit (1 bit, active high). This design supports configurable 16-32 data bits, with a default of 24 data bits, corresponding to a 24-bit displacement resolution. It supports switching between odd parity, even parity, and no parity, with odd parity as the default, used to detect transmission errors. The timing generation unit strictly adheres to the SSI timing specification; data is updated on the falling edge of the clock and stabilized on the rising edge. Setup and hold times meet nanosecond-level requirements, ensuring reliable sampling by the master device. It supports clock frequencies up to 2MHz, adapting to high-speed data acquisition needs. SSI output module 105; The SSI signal output by the microcontroller is a TTL single-ended level, which has poor anti-interference capability and is not suitable for long-distance transmission. The function of the SSI output module 105 is to convert the TTL single-ended signal into an RS-485 differential signal, which conforms to the electrical standards of the SSI interface, improves the signal transmission distance and anti-interference capability. This module uses the MAX3490ESA+T type RS-485 transceiver. This chip supports a maximum transmission rate of 10Mbps, which fully meets the requirements of high-speed SSI transmission; it has ±15kV electrostatic protection capability, industrial-grade temperature range, and high reliability. The differential output level conforms to the EIA / TIA-485 standard. With a 120Ω terminating resistor, the transmission distance can reach hundreds of meters, and the signal has no attenuation and strong anti-interference capability. The SSI interface includes two pairs of differential signal lines: one pair is the clock line (CLK+, CLK-) driven by the master device; the other pair is the data line (DATA+, DATA-) driven by this device. The clock signal is input to the timing generation unit of the microcontroller, and the data signal is output by the microcontroller and then converted into a differential signal output by the RS-485 chip. The signal output by this module fully conforms to the SSI international standard and can be directly connected to SSI interface data acquisition devices and PLCs from mainstream brands such as Siemens, Beckhoff, and Advantech, achieving true plug-and-play functionality without any additional protocol conversion or secondary development.

[0034] Example 2: like Figure 1-3 As shown, an electronic device for digitizing analog displacement sensors adopts an integrated shielding structure, which takes into account electromagnetic shielding, ease of installation and industrial protection capabilities. The device has a cylindrical, elongated structure, approximately 120mm in length and 35mm in diameter. Its compact size makes it easy to install next to sensors or inside control cabinets. Input and output interfaces are located at both ends, and an operation switch is located on the side. Internally, it integrates two PCBs and a shielding structure. From left to right, the components are: SSI signal male connector 1, SSI digital signal generation board (PCB1) 2, shielding shell 3, mode switch 5, fixing bolts 6, analog signal acquisition board (PCB2) 7, and analog signal female connector 8. The two internal PCBs are coaxially fixed by fixing bolts 6, with a gap in between and a metal shielding layer installed to achieve physical isolation between the analog and digital circuits. The shielding shell 3 is made of 6061 aluminum alloy profile with a wall thickness of 1.5mm. The surface is treated with conductive oxidation to form a continuous conductive shield. The aluminum alloy shell has excellent electromagnetic shielding performance and has a good shielding effect on both electric and magnetic fields. The overall shielding effectiveness is ≥60dB, which can effectively attenuate external electromagnetic interference and prevent high-frequency noise from internal digital circuits from radiating outward and affecting analog circuits. The two ends of the shell are sealed with end caps, and conductive rubber strips are installed between the end caps and the shell to achieve 360° continuous conductive contact and avoid leakage from shielding gaps. The shell is designed with mounting ears, which can be used to fix the device to the equipment frame or mounting rail with screws. The device uses two independent PCB boards to separate the analog and digital circuits, reducing digital interference coupling to the analog circuits. Analog signal acquisition board (PCB2) 7: integrates all analog circuits such as overvoltage protection module and current-voltage signal conversion module. It is located close to analog signal female connector 8 to shorten the length of analog signal traces and reduce interference pickup. This board is designed with pure analog ground and single-point connection to digital ground to avoid ground loop interference. SSI Digital Signal Generation Board (PCB1) 2: Integrates digital circuits such as analog-to-digital conversion module, microcontroller module, and SSI output module. It is located near SSI signal male connector 1. This board is designed for digital ground and is connected to analog ground at a single point through a ferrite bead to block digital noise from being conducted to the analog side. A thin copper shielding layer is added between the two PCBs to completely separate the analog area and the digital area, further improving the isolation effect. The PCBs are all made of industrial-grade FR-4 substrate and immersion gold process to ensure long-term operational reliability. Analog signal female connector 8: Utilizes an M12 industrial-grade circular shielded connector with a 4-pin design, supporting wiring for both voltage and current sensors. It features IP67 waterproof and dustproof protection, suitable for outdoor and industrial applications. The connector housing and shielding housing are seamlessly integrated 360°, ensuring continuous shielding. SSI Signal Male Connector 1: Adopts a standard SSI interface circular connector with a 5-pin design, including clock differential pairs, data differential pairs, and shielded ground. It is fully compatible with standard SSI sensor cables, and users can directly use their existing SSI sensor cables without the need for custom cables. Mode switch 5: This waterproof toggle switch is mounted on the side of the housing. Its moderate protrusion height makes it easy to operate with your fingers, and it is also waterproof and dustproof. The switch positions are clearly marked with "V" (voltage) and "I" (current) indicators, allowing users to intuitively select the operating mode. Fixing bolt 6: Stainless steel internal hex bolts are used to fix the internal PCB board and end cover, ensuring a solid structure, strong resistance to vibration and impact, and meeting the vibration environment requirements of industrial equipment. The accompanying signal cable 4 is a dedicated double-shielded signal cable, with an inner layer of aluminum foil shielding and an outer layer of braided copper mesh shielding, achieving a shielding coverage of ≥95%. The cable shielding layer is 360° connected to the connector housing, with single-end grounding, forming a complete shielded link to minimize interference pickup on the cable.

[0035] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0036] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0037] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An electronic device for digitizing an analog displacement sensor, characterized in that: The system includes an overvoltage protection module, a current-to-voltage signal conversion module, an analog-to-digital conversion module, a microcontroller module, and an SSI output module, which are connected in sequence. It also includes a mode switching switch, a shielded enclosure, an analog signal acquisition board, and an SSI digital signal generation board. The mode switching switch is electrically connected to the control terminal of the current-to-voltage signal conversion module and is used to switch between voltage input mode and current input mode. The overvoltage protection module serves as the signal input terminal of the device, used to receive the analog signal output by the analog displacement sensor and suppress transient overvoltages; the current-to-voltage signal conversion module converts a 4-20mA current signal into a 0-10V voltage signal in current input mode, and directly conducts the 0-10V voltage signal in voltage input mode; the analog-to-digital conversion module converts the analog voltage signal into a parallel digital signal and transmits it to the microcontroller module; the microcontroller module calibrates the digital signal and generates serial data conforming to the SSI protocol specification; the SSI output module converts the serial data into a standard differential SSI signal and outputs it to an external data acquisition device; The analog signal acquisition board and the SSI digital signal generation board are arranged in layers inside the shielded shell, with a metal shielding layer in between; the overvoltage protection module and the current-voltage signal conversion module are integrated into the analog signal acquisition board. The analog-to-digital conversion module, the microcontroller module, and the SSI output module are integrated into the SSI digital signal generation board. The shielding shell is made of aluminum alloy with a conductive oxidation treatment on the surface, and the electromagnetic shielding effectiveness is ≥60dB. One end of the shielding shell is equipped with an analog signal female connector, the other end is equipped with an SSI signal male connector, a mode switching switch is provided on the side, and fixing bolts are provided at the bottom.

2. The electronic device for digitizing an analog displacement sensor according to claim 1, characterized in that: The overvoltage protection module includes a transient suppression diode and a current-limiting resistor. The transient suppression diode is connected in parallel between the signal input path and ground, with a response time of less than 1ps and a breakdown voltage covering a range of 0-30V. It is used to absorb surge voltage and electrostatic pulses in industrial environments.

3. The electronic device for digitizing an analog displacement sensor according to claim 1, characterized in that: The current-voltage signal conversion module includes a sampling unit, an input filtering unit, a range calibration unit, and a differential amplification unit. The sampling unit includes a high-precision low-temperature drift sampling resistor with a resistance of 500Ω, an accuracy class of ±0.01%, a temperature coefficient of ≤5ppm / ℃, a rated power of ≥300mW, and is connected to the signal circuit using a four-wire connection method. The input filtering unit is an RC low-pass filter, consisting of a 100Ω precision resistor and a 0.1μF ceramic capacitor, with a cutoff frequency of approximately 15.9kHz, used to suppress high-frequency electromagnetic interference. The range calibration unit includes a zero-adjustment potentiometer and a full-scale potentiometer. The zero-adjustment potentiometer has a resistance of 10kΩ and is used to calibrate the zero-point parameter corresponding to 0V output for a 4mA input. The full-scale potentiometer has a resistance of 100kΩ and is used to calibrate the full-scale parameter corresponding to 10V output for a 20mA input. The differential amplifier unit uses an instrumentation amplifier with a common-mode rejection ratio ≥100dB to amplify the differential voltage across the sampling resistor to the 0-10V standard range.

4. The electronic device for digitizing an analog displacement sensor according to claim 1, characterized in that: The differential amplifier unit uses Texas Instruments OPA series instrumentation amplifiers with an input offset voltage of less than 10μV, an offset voltage temperature drift of less than 0.1μV / ℃, a gain error of less than 0.01%, and a gain temperature drift of less than 1ppm / ℃.

5. An electronic device for digitizing an analog displacement sensor according to claim 1, characterized in that: The analog-to-digital converter module adopts a 24-bit ΔΣ type analog-to-digital converter, supports four-channel synchronous sampling, has a maximum sampling rate of 128kSPS, and an effective resolution of 20.6 bits at a sampling rate of 8kSPS. It has a built-in programmable gain amplifier and digital filter, and supports communication with the microcontroller module via the SPI interface.

6. An electronic device for digitizing an analog displacement sensor according to claim 1, characterized in that: The microcontroller module uses a 32-bit microcontroller with built-in Flash and RAM memory, and operates at a frequency of no less than 72MHz. The microcontroller module includes a sampling control unit, a data calibration unit, and a timing generation unit. The sampling control unit is used to configure the sampling rate, gain, and channel parameters of the analog-to-digital conversion module. The data calibration unit includes a linear calibration algorithm, a temperature drift compensation algorithm, and a digital filtering algorithm to correct signal conversion errors. The timing generation unit is used to generate a synchronous clock and data frame timing conforming to the SSI international standard.

7. An electronic device for digitizing an analog displacement sensor according to claim 1, characterized in that: The SSI output module includes an RS-485 transceiver chip, supports a maximum transmission rate of 10Mbps, and outputs differential levels that conform to the SSI interface electrical specifications. The SSI signal frame output by the SSI output module includes a start bit, data bits, parity bit, and stop bit. The data bit length is configurable from 16 to 32 bits, and the parity mode supports switching between odd parity, even parity, and no parity, making it compatible with mainstream industrial SSI interface data acquisition devices.

8. A detection method for digitizing an analog displacement sensor, implemented based on the electronic device according to any one of claims 1-7, characterized in that: The detection method specifically includes the following steps: Step 1: Working mode selection: According to the output type of the analog displacement sensor to be connected, toggle the mode switch to the corresponding position and select the voltage input mode or the current input mode; Step 2: Wiring the analog displacement sensor; Connect the signal output terminal of the analog displacement sensor to the analog signal female connector of the electronic device through a shielded cable, confirming that the wiring polarity is correct, the connection is secure, and the shielding layer is reliably grounded at one end. Step 3: Wiring the digital acquisition system; Connect the SSI signal male connector of the electronic device to the SSI standard interface of the data acquisition system through the dedicated SSI shielded cable, and confirm that the cable termination resistance is matched and the connection is secure; Step 4: System power-on and parameter configuration; sequentially connect the power supplies to the analog displacement sensor, electronic device and data acquisition system, configure the SSI interface parameters on the data acquisition system, and complete device identification and communication establishment; Step 5: System calibration and accuracy verification; Perform zero-point calibration and full-scale calibration on the electronic device. After calibration, input a standard displacement signal to verify the accuracy, linearity, and stability of the output data and confirm that it meets the measurement requirements. Step 6; Formal Test and Data Acquisition; Start the test process. The data acquisition system synchronously reads the displacement data of each channel through the SSI interface, monitors the displacement changes in real time, and records the data of the entire test process. Step 7: End of test and equipment removal; After the test is completed, first disconnect the power supply to the data acquisition system and electronic devices, then disconnect the SSI side cables and analog sensor side cables in sequence, and organize and store the equipment.

9. The detection method for digitizing an analog displacement sensor according to claim 8, characterized in that: In step 1, when the current input mode is selected, the mode switching switch connects the signal path between the sampling unit and the differential amplifier unit, and the 4-20mA current signal is converted into a voltage signal and then output; when the voltage input mode is selected, the mode switching switch bypasses the sampling unit and the differential amplifier unit, and the 0-10V voltage signal is directly input to the analog-to-digital converter module after filtering.

10. A detection method for digitizing an analog displacement sensor according to claim 8, characterized in that: The SSI interface parameter configuration in step 4 specifically includes setting the SSI clock frequency to 100kHz-2MHz, setting the data bit length to 24 bits, setting the parity method to odd parity, and setting the data encoding format to binary encoding. After configuration, the data acquisition system actively sends a clock synchronization signal, and the electronic device returns device identification data, completing the handshake connection.

11. The detection method for digitizing an analog displacement sensor according to claim 8, characterized in that: The specific procedures for zero-point calibration and full-scale calibration in step 5 are as follows: Step 501: Zero-point calibration; Place the analog displacement sensor at the zero-displacement reference position. After the signal stabilizes, trigger the zero-point calibration command at the data acquisition system. The electronic device records the current ADC sampling value and stores it as the zero-point reference value. Step 502: Full-scale calibration; The analog displacement sensor is placed at the full-scale displacement reference position. After the signal stabilizes, the full-scale calibration command is triggered. The electronic device records the current ADC sampling value and stores it as the full-scale reference value. Step 503: Linear fitting; The microcontroller module establishes a linear mapping relationship between the ADC sampled value and the actual displacement value based on the zero-point reference value and the full-scale reference value, and completes the basic range calibration.

12. The detection method for digitizing an analog displacement sensor according to claim 11, characterized in that: Step 5 also includes multi-point linear calibration, specifically, at least 5 calibration points are uniformly selected within the measurement range, the standard displacement signal corresponding to each point is input sequentially, the ADC sampling value and standard displacement value of each calibration point are recorded, a high-order linear correction curve is obtained by fitting with the least squares method, and stored in the non-volatile memory of the microcontroller module to correct nonlinear errors within the full measurement range.

13. The detection method for digitizing an analog displacement sensor according to claim 8, characterized in that: In step 6, the data acquisition system uses an SSI synchronization clock to achieve synchronous acquisition of multiple electronic devices with a synchronization error of less than 1μs. The microcontroller module performs moving average filtering and outlier removal on the sampled data. The data update rate supports up to 8kHz, and the total signal transmission delay is less than 1ms.

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