Abstract: This paper introduces a method for implementing an accelerometer performance test bench based on the 2.4G RF chip nRF2401. The testing principle of the accelerometer performance and the implementation method of the test bench are detailed. In this system, the output signal of the accelerometer is acquired by a PIC16F877A microcontroller and then transmitted to an industrial control computer via the RF chip nRF2401. NI LabVIEW is used to analyze the acquired data. RF technology solves the problem of wiring between rotating and stationary parts in data acquisition, enabling accurate and rapid data acquisition. Keywords: Accelerometer; nRF2401; Test platform; PIC single-chip computer; LabVIEW Abstract: This thesis introduces the method of realizing acceleration sensor performance test platform based on 2.4G radio frequency chip nRF2401, and details the test principle and method of realizing acceleration sensor performance test platform. In this system, a PIC16F877A PIC single-chip computer is used to collect the data sent from the acceleration sensor. The sensor transmits the data to an industrial control computer via the nRF2401 radio frequency chip, and simultaneously analyzes the collected data using NI LabVIEW. The radio frequency technology solves the problem of wiring difficulties between the rotating part and the standstill part during the data acquisition process, and enables fast and accurate data collection. Key words: Accelerometer; nRF2401; Test platform; PIC single-chip computer; LabVIEW. 0 Introduction This paper introduces how to use radio frequency technology to build an automatic test platform to realize the performance testing of an acceleration sensor. Accelerometers are widely used in the automotive field, primarily for applications such as airbags, rollover detection, collision detection, vehicle dynamic control, braking control systems, and driver safety devices. Generally, accelerometer output signals are available in two forms: analog voltage output and digital output. This accelerometer performance test bench tests accelerometers with analog voltage output. According to the technical specifications provided by the accelerometer manufacturer, under normal conditions, the output voltage of the accelerometer is linearly related to the acceleration it experiences, or conforms to a given curve. If the measured value matches the given curve, the accelerometer performance is considered合格 (qualified); otherwise, it is不合格 (unqualified). 1 Test Principle and Test Method [align=center] Figure 1 Schematic diagram of centripetal acceleration of an object on a uniform speed turntable[/align] To test the performance of an accelerometer, it must be subjected to various acceleration conditions to produce different output voltages. Therefore, the first requirement of this automatic accelerometer test bench is to generate different acceleration conditions. The testing principle of this system is as follows: When an object rotates at a constant speed, it generates centripetal acceleration. For a given radius, different rotational speeds result in different centripetal accelerations, and the magnitude of the centripetal acceleration is directly proportional to the rotational speed. An accelerometer moving at different speeds on a circle of fixed radius can generate different centripetal accelerations, resulting in different voltage output values, thus allowing for the testing of the accelerometer's performance indicators. As shown in Figure 1, accelerometer A is mounted on a uniformly rotating disk with a radius of R (meters). Let the disk's rotational speed be n (revolutions/minute), its angular velocity be ω (radians/second), and the linear velocity of the object be v (meters/second). The centripetal force of the object is F (Newtons), and the centripetal acceleration is a (meters/second²). The direction of acceleration points towards the center of the circle, i.e., perpendicular to the object's direction of motion. From the above, it can be deduced that by changing the rotational speed of the disk, the accelerometer can be subjected to different acceleration conditions. Therefore, the testing method of this system is as follows: the accelerometer is fixed on a uniformly rotating disk, which is driven by a motor to rotate at a uniform speed, and the speed of the motor is controlled by an industrial control computer. Each time the motor speed is changed, the accelerometer will generate an output voltage at a different acceleration value. Therefore, the output voltage value of the accelerometer at various acceleration values ​​can be measured. 2. System Structure of the Accelerometer Performance Test Bench This automatic accelerometer performance test bench uses NI LabVIEW as the development platform. Radio frequency (RF) technology is used to solve the wiring problem between the rotating and stationary parts in data acquisition. Figure 2 shows the system structure diagram of this automatic accelerometer performance test bench. The system consists of an industrial control computer, interface circuit, motor speed control system, motor, sampling system, and a test bench for the sensor under test. The sampling system rotates together with the accelerometer under test, while the interface circuit and industrial control computer remain stationary. Signal transmission between the sampling system and the interface circuit is via RF. The sensor under test is fixed on a disk on the test bench, and the radius of the disk is 0.2 meters. The disk is driven to rotate by a servo motor, which is controlled by a motor speed control system. The industrial control computer controls the motor speed via a serial port. The interface circuit obtains data from the sampling system via radio frequency transmission and transmits this data to the industrial control computer via a serial port. [align=center]Figure 2 Block diagram of the automatic test bench system for accelerometers[/align] Since the sampling system rotates together with the accelerometer under test, while the industrial control computer and interface circuit are stationary, how to extract the signal from this rotating component is one of the challenges of this project. Currently, the internationally accepted methods for measuring signals from rotating components are current collector transmission and wireless transmission. Current collector transmission methods include three types: wire-type, inductive, and brush-type. The wire-type current collector is prone to wear during use and is suitable for signal measurement of low-speed rotating parts; the change in the gap between the moving and stationary coils of the inductive current collector will cause the change in magnetic resistance when it is working, thus affecting the measurement results, and the rotation speed of the rotating parts it measures is not high; the brush current collector has better working performance and can be used for signal measurement at higher speeds, but when rotating at high speeds, the stator/rotor of the brush current collector will heat up and cause signal drift, thus resulting in measurement errors. Wireless transmission methods include infrared transmission and radio transmission. The carrier of infrared transmission is infrared light. Since infrared light has a certain directionality and cannot penetrate obstacles, infrared transmission is only suitable for data transmission in close-range, small-angle, and obstacle-free situations. Therefore, this system adopts wireless digital transmission technology with strong anti-interference ability. 3 Implementation method of accelerometer performance test bench From the system structure of the automatic accelerometer performance test bench, it can be seen that the implementation of the test bench mainly consists of the following parts: (1) Sampling system The function of the sampling system is to collect the sensor signal and realize the reception and transmission of data through the radio frequency transceiver circuit. This system uses the MICROCHIP PIC16F877A microcontroller as the processor for the sampling system. This microcontroller was chosen because of its following advantages: ① It uses a high-performance RISC CPU, requiring only 35 single-word instructions to learn programming; ② It has a fast instruction execution speed, with a clock input range of 0–20MHz, and all instructions except program branches are single-cycle instructions; ③ It has a wide operating voltage range of 2.0–5.5V; ④ It supports In-Circuit Serial Programming™ (ICSP); ⑤ It has a 10-bit multi-channel A/D converter; ⑥ It has a Synchronous Serial Port (SSP) with SPI™ (master mode) and I2C (master/slave) capabilities. The accelerometer tested on this test bench is an analog voltage output type. Therefore, the main interface of the microcontroller in the sampling system is the analog signal input of the accelerometer and the interface with the radio frequency module. The radio frequency chip used is nRF2401. Its data communication interface is a synchronous serial interface in SPI mode, so it can be directly connected to the SSP port of the microcontroller. (2) Radio frequency transceiver circuit In order to solve the problem of difficult wiring between the rotating part and the stationary part in data acquisition, radio frequency technology is used for data transmission in this design. The radio frequency chip used is Nordic's radio frequency transceiver chip nRF2401. nRF2401 is a single-chip integrated receiver and transmitter chip. The operating frequency range is the globally open 2.4 GHz band. The data rate when using GFSK modulation is a high rate of 1 M bit/s, which is higher than Bluetooth and has a high data throughput. nRF2401 has built-in CRC error correction and detection hardware circuit and protocol. All operating parameters such as transmission power and operating frequency are all set by software. 1.9～3.6 V low power consumption, which meets the low power consumption design requirements. Each chip can be set to a maximum of 40 bits of address via software. It will only output data and provide an interrupt indicator when it receives the local address. The chip is easy to program and can meet the needs of this system. To achieve data transmission and reception, at least two radio frequency transceiver modules are required. In this system, one radio frequency transceiver module is used in the sampling system and one in the interface circuit to achieve point-to-point data transmission. The radio frequency transceiver module in the interface circuit is responsible for data transmission with the industrial control computer. It plays the role of a data relay. The radio frequency module in the sampling system is responsible for transmitting the data generated by the acceleration sensor collected by the acquisition system to the industrial control computer. (3) Motor speed control system Since the system uses a motor to drive the disk to rotate to generate acceleration conditions, a motor and a motor speed control system are required. In this system, a DC servo motor is selected as the motor, and the motor speed control system adopts the DDS series digital speed control system. It uses a DC motor and a tachometer unit, with the 8751 microcontroller as the core, digital input, software PID adjustment, and digital PWM output. IGBT power drive is a high-precision, low-drift bidirectional speed control system. The motor speed control system can be controlled by an industrial computer. The industrial computer can send corresponding instructions through the serial port to make the motor work at a certain speed, so that the accelerometer has a voltage output at a certain acceleration value. (4) Data acquisition and signal analysis software NI LabVIEW is a graphical programming language used for data acquisition, analysis and display graphical development environment to quickly create flexible and upgradeable test, measurement and control applications. Using LabVIEW, actual signals can be acquired and analyzed to obtain useful information. Then the measurement results and application are analyzed. This design uses NI LabVIEW instead of VB or VC as the programming language because LabVIEW has powerful signal analysis functions and can quickly and conveniently develop data acquisition and signal analysis software for the system. After the data enters the industrial computer through the serial port, LabVIEW reads the data and performs digital filtering. After curve fitting, it is compared with the given curve to determine whether the accelerometer performance is qualified. 4 Conclusion In the design process of the accelerometer performance test bench, the first thing to solve is the problem of generating acceleration conditions. The method of uniform rotation to generate acceleration conditions is a relatively easy method to implement and the accuracy is also relatively easy to control. However, a drawback of this method is the difficulty in wiring the rotating and stationary mechanisms. This problem is easily solved by using radio frequency (RF) technology for wireless data transmission. Furthermore, NI LabVIEW's powerful data acquisition and signal analysis capabilities make the design process convenient and fast. The authors' innovations include: using the method of generating centripetal acceleration from a rotating object to create the conditions for acceleration generation on the accelerometer performance test bench; and using RF technology to solve the problem of wiring difficulties between the rotating and stationary parts. References: [1] Wang Yuqian, Yang Jiming, Dong Shunyi, Li Wei. Measurement method of engine vibration velocity displacement and acceleration based on microcontroller[J]. Microcomputer Information, 2005, 7: 62-63. [2] Bian Chunjiang, Zhang Tianhong, Deng Zhiwei, Zhang Ping. High-speed wireless data acquisition system for rotating components[J]. Sensor Technology, 2004, 11: 53-55. [3] Hou Guoping, Wang Kun, Ye Qixin. LabVIEW7.1 Programming and Virtual Instrument Design[M]. Beijing: Tsinghua University Press, 2005: 17-219. [4] Liu Duren. PIC Software and Hardware System Design[M]. Beijing: Electronic Industry Press, 2005: 26-36.