Acceleration sensor performance test bench design
Abstract: This paper introduces an implementation method of accelerometer performance test bench based on 2.4G radio frequency chip nRF2401. The test principle of accelerometer performance and the implementation method of accelerometer performance test bench are introduced in detail. In this system, the PIC microcontroller PIC16F877A is used to collect the output signal of the accelerometer and then transmit it to the industrial computer through the RF chip nRF2401. At the same time, the collected data is analyzed by NI LabVIEW. The radio frequency technology solves the problem of difficult wiring between the rotating part and the stationary part in data acquisition, so that the data can be collected correctly and quickly.
This article describes how to use RF technology to build an automated test bench to achieve performance testing of acceleration sensors. Accelerometers are widely used in the automotive field. They are mainly used in the following areas: airbags, rollover detection, collision detection, vehicle dynamics control, brake control systems, and driver safety devices. In general, the output signal of the acceleration sensor is divided into two modes: analog voltage output mode and digital output mode. The acceleration sensor performance test bench tests the acceleration sensor of the analog voltage output mode. According to the technical indicators provided by the manufacturer of the accelerometer, under normal circumstances, the output voltage of the accelerometer is linear with the acceleration applied to it, or conforms to a given curve, if the value obtained by the test matches the given curve. It indicates that the acceleration sensor is qualified, otherwise it is unqualified.
1 Test principle and test method
Figure 1 Schematic diagram of the centripetal acceleration of the object on the uniform speed dial
To test the performance of the accelerometer, it must be under different acceleration conditions to have different output voltages. Therefore, the accelerometer automatic test bench first needs to generate different acceleration conditions. The test principle of this system is: when the object rotates at a constant speed, it can produce centripetal acceleration. When the radius is constant and the rate of uniform rotation is different, the centripetal acceleration generated is also different. The magnitude of the centripetal acceleration is proportional to the rate of rotation. The acceleration sensor can make different centripetal accelerations at different speeds on the circumference of the fixed radius at different speeds, thus generating different voltage output values, so that the performance index of the acceleration sensor can be tested.
As shown in Fig. 1, the acceleration sensor A is mounted on a uniformly rotating disk having a radius of R (m), and the rotational speed of the disk is n (r/min), and the angular velocity of the disk is ω (radian/second). The linear velocity of the object motion is v (m/s). The centripetal force of the object is F (cow), and the centripetal acceleration is a (m/s 2). The acceleration direction points to the center of the circle, that is, perpendicular to the direction of motion of the object.
It can be known from the above that as long as the rotational speed of the disk is changed, the acceleration sensor can be subjected to different acceleration conditions. Therefore, the test method of the system is: fixing the acceleration sensor on a rotating disk at a constant speed, the disk is driven by the motor to rotate at a constant speed, and the speed of the motor is controlled by the industrial computer. Each time the motor speed is changed, the acceleration sensor produces an output voltage at a different acceleration value. Therefore, the output voltage value of the acceleration sensor at each acceleration value can be measured.
2 Acceleration sensor performance test system structure
This accelerometer performance automatic test bench uses NI LabVIEW as the development platform, and uses radio frequency technology to solve the wiring problem between rotating parts and stationary parts in data acquisition. Figure 2 shows the system structure diagram of the automatic test bench for the acceleration sensor performance. The system consists of industrial computer, interface circuit, motor speed control system, motor, sampling system and test station. The sampling system rotates together with the measured acceleration sensor, and the interface circuit and the industrial computer are at rest. The signal transmission between the sampling system and the interface circuit is performed by radio frequency. The sensor under test is fixed on the disc of the test bench with a radius of 0.2 m. The disc is driven to rotate by a motor. The motor uses a servo motor, which is driven by a motor speed control system. The industrial computer controls the speed of the motor through a serial port. The interface circuit obtains the data of the sampling system through radio frequency transmission, and the data is transmitted to the industrial computer through the serial port.
Figure 2 Acceleration sensor automatic test bench system block diagram
Since the sampling system rotates together with the measured acceleration sensor, the industrial computer and the interface circuit are in a stationary state. How to draw the signal of the rotating component is one of the difficulties of this topic. At present, the methods commonly used to measure rotating component signals in the world include current collector transmission and wireless transmission. Collector transmission methods include cable, inductive and brush. The wire-type current collector is easy to wear when used, and is suitable for signal measurement of low-speed rotating parts; when the inductive current collector is working, the change of the gap between the dynamic and dynamic coils causes a change in the magnetic resistance, thereby affecting the measurement result, and the measurement thereof The rotational speed of the rotating component is not high; the brush-type current collector has better working performance and can be used for signal measurement at higher speeds, but when rotating at high speed, the stator/rotor heating of the brush current collector will cause signal drift, and measurement errors will occur. Wireless transmission methods include infrared transmission and radio transmission. The infrared transmission carrier is infrared. Since infrared rays have a certain directivity and cannot pass through obstacles, infrared transmission is only suitable for data transmission in close-range, small-angle, and obstacle-free applications. Therefore, the system adopts wireless digital transmission technology with strong anti-interference ability.
3 Acceleration sensor performance test bench implementation method
It can be seen from the system structure of the automatic test bench of the acceleration sensor performance that the implementation of the test bench is mainly composed of the following parts:
(1) Sampling system
The function of the sampling system is to collect the signal of the sensor and receive and transmit the data through the RF transceiver circuit. This system uses MICROCHIP's PIC16F877A single-chip microcomputer as the processor of the sampling system. The single-chip microcomputer is selected as long as it has the following advantages:
1 Using the high-performance condensed instruction set RISC CPU, you can learn to program as long as you learn 35 single-word instructions;
2 The instruction execution speed is fast, the clock input is allowed to be in the range of 0~20MHZ, and the instruction is a single-cycle instruction except that the program branch has two cycles;
3 Wide operating voltage range: 2.0 to 5.5V;
4 Supports in-circuit serial programming (ICSP);
5 10-bit multi-channel A/D converter;
6 Synchronous Serial Port (SSP) with SPITM (Master Mode) and I2C (Master/Slave).
The accelerometer tested by this test bench is analog voltage output mode. Therefore, the main interface of the MCU in the sampling system is the analog signal input of the accelerometer and the interface with the RF module. The RF chip adopts nRF2401, and its data communication interface is an SPI. The synchronous serial interface of the mode, so it can be directly connected to the SSP port of the microcontroller.
(2) RF transceiver circuit
In order to solve the problem of difficult wiring between the rotating part and the stationary part in data acquisition, the radio frequency technology is used for data transmission in this design. The radio frequency chip adopts the RF transceiver chip nRF2401 of Nordic Company.
The nRF2401 is a monolithic integrated receiver and transmitter chip that operates over the global 2.4 GHz band. The data rate when using GFSK modulation is a high rate of 1 M bit / s, higher than Bluetooth, with high data throughput. The nRF2401 has built-in CRC correction and error detection hardware circuits and protocols. All operating parameters such as transmit power and operating frequency are all set by software. 1.9 ~ 3.6 V low power consumption, to meet the needs of low power design. Each chip can be set up to 40bit address by software, and will only output data and provide an interrupt indication 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 RF transceiver modules must be used. In this system, one RF transceiver module is used in the sampling system and interface circuit to realize point-to-point data transmission. The RF transceiver module in the interface circuit is responsible for data transmission with the industrial computer, which acts as a data relay. The function of the RF module in the sampling system is to realize the data generated by the acceleration sensor collected by the industrial control and transmission acquisition system.
(3) Motor speed control system
Since the motor is driven by the rotation of the disk to generate acceleration conditions, the motor and motor speed control system are used. The motor in this system uses DC servo motor, and the motor speed control system adopts DDS series digital speed control system. It adopts DC motor and speed measuring machine unit, with single-chip microcomputer 8751 as the core, digital quantity given, software PID adjustment, 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 the industrial computer. The industrial computer can send the corresponding command through the serial port to make the motor work at a certain speed, so that the acceleration sensor has a voltage output under a certain acceleration value.
(4) Data acquisition and signal analysis software
NI LabVIEW is a graphical programming language for graphical development environments for data acquisition, analysis, and display to quickly create flexible, scalable test, measurement, and control applications. LabVIEW captures the actual signal and analyzes it to produce useful information, then analyzes the measurement and the application. This design uses NI LabVIEW instead of VB or VC as the programming language. It is because of the powerful signal analysis function of LabVIEW that can quickly and easily develop applications and data acquisition and signal analysis software.
After the data enters the industrial computer through the serial port, LabVIEW reads the data and performs digital filtering. After the curve is fitted and compared with the given curve, it can be judged whether the performance of the acceleration sensor is qualified.
4 Conclusion
In the design process of the acceleration sensor performance test bench, the first problem to be solved is the problem of the acceleration condition. The method of generating the acceleration condition by the uniform rotation method is a relatively easy to implement method and the accuracy is relatively easy to control. However, one drawback of this method is the difficulty in wiring the rotating mechanism and the stationary mechanism, and the use of radio frequency technology to achieve wireless transmission of data solves the problem. And NI LabVIEW makes design quick and easy with its powerful data acquisition and signal analysis capabilities.
The author of this paper innovates: the use of rotating objects to generate centripetal acceleration to create acceleration conditions for the acceleration sensor performance test bench; the use of radio frequency technology to solve the problem of difficult wiring between the rotating part and the stationary part.
references:
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[2] Yan 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 Yuren. Design of PIC software and hardware system [M]. Beijing: Publishing House of Electronics Industry, 2005: 26-36.
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