Abstract: This paper designs a testing platform for the reliability of AC contactor operation by combining the implementation of a data acquisition system and the application of LabVIEW. It introduces and discusses the basic principles, design ideas, implementation methods, and related technologies of its hardware and software system and virtual instrument development. Experimental tests show that the developed data acquisition system can perform real-time sampling and data analysis of the actual operation process of AC contactor contacts. It proposes using the bounce change during contact and the time difference between the closing of each contact as technical indicators to verify the reliability of contactor operation. Keywords: AC contactor; data acquisition; computer bus; virtual instrument; dynamic link library 1 Introduction AC contactors are a widely used low-voltage electrical product, extensively applied in power systems and control systems. Therefore, improving their quality and reliability is crucial. The closing and opening forces of a contactor include the electromagnet's attraction in addition to the spring. The electromagnet's attraction during closing is related to the closing phase angle and is random; the electromagnet's attraction during opening is related to the excitation current phase angle and is also random. At the moment of contact closure, mechanical factors can cause some bouncing, resulting in multiple instantaneous opening and closing, which degrades the actual operating conditions of the contactor. For dedicated contactors controlling capacitors, the randomness of contact movement speed during closure causes randomness in the contact time difference between different phase contacts, making it impossible to control the magnitude of the inrush current when connecting the capacitor. Therefore, the requirements for the consistency of the pull-in time are even more stringent for such contactors. The contactor contact opening and closing process is usually detected using a stepper motor to drive the contacts. The entire opening and closing process is accomplished by the stepper motor's movement; the displacement of the contacts from open to closed is also obtained by counting the stepper motor's step pulses. This detection is a static detection method and cannot truly reflect the entire contactor's pull-in process, nor can it detect the bouncing changes of the contacts during actual operation or the actual pull-in time difference between each contact. To ensure the reliability of the contactor, it is necessary to develop a data acquisition system that records the contactor's actual contact opening and closing process to evaluate the contactor's performance. 2 System Hardware and Working Principle To sample high-speed transient signals and distinguish the bounce process and contact sequence when AC contactor contacts are closed, a technical solution based on a PC ISA bus and synchronous clock was designed to achieve high-speed synchronous data acquisition, high-speed addressing, and real-time storage using hardware circuitry. This solution mainly consists of four parts: a PC bus interface circuit, a high-speed digital signal acquisition and storage circuit, an I/O interface circuit, and a contactor power supply circuit. Its hardware system structure diagram is shown in Figure 1. [align=center] Figure 1 Hardware System Structure Diagram[/align] 2.1 PC Bus Interface Circuit This system uses Advantech's industrial control computer, utilizing its ISA (Industry Standard Architecture) bus for external addressing. The ISA bus uses an 8-bit mode with a maximum data transfer rate of 8MBps, facilitating interface with external hardware. Its performance is sufficient to meet the requirements of data acquisition equipment, and the technology is mature and easy to develop. The ISA bus is divided into five categories: address lines, data lines, control lines, auxiliary lines, and power lines. The first 256 I/O port addresses (0x00H-0xFFH) can be accessed by both fixed I/O instructions and variable I/O instructions, but any I/O address in the range of 0x0100H-0xFFFFH can only be accessed by variable I/O addresses. In a PC, all 16-bit address buses are translated into addresses in the range of 0x0000H-0x03XXH for use as internal I/O addresses on the ISA bus. The PC's ISA bus, after passing through bus transceiver and address decoding circuits, provides the data acquisition device with an addressing range of 0x300H-0x31BH. The PC bus interface circuit is shown in Figure 2. When the PC needs to access a certain address, two GAL16V8 chips decode read/write and enable signals to select the 74HC245 bus transceiver to transmit 8 bits of data. [align=center]Figure 2 PC Bus Interface Circuit[/align] 2.2 High-Speed ​​Digital Signal Acquisition and Storage Circuit The principle of the high-speed digital signal acquisition and storage circuit is shown in Figure 3. It consists of several parts, including a data transceiver and control circuit, a frequency generator, an address generator, a data read/write signal decoder, a sampling logic switching circuit, an address latch, a data storage circuit, and a storage sampling data logic switching circuit. The main technical specifications are: 16-channel digital signal acquisition, a sampling rate of 625kHz, a storage depth of 64Ksa/CH, a maximum number of sampling points of 65536, and a maximum sampling storage time of 100ms. The data transceiver and control circuit consists of a bus transceiver, a GAL decoder, and a parallel interface chip 8255, completing the data reading and circuit control functions in the SRAM. The frequency generator consists of a crystal oscillator and a pre-programmable four-bit binary asynchronous clear counter 74HC161. The sampling rate is obtained by multiplying the 10MHz oscillator by 16 times using the counter 74HC16, i.e., the system sampling frequency is 625kHz. Its output is controlled by the sampling logic switching circuit, and the output clock is sent to the address generator and the data read/write signal decoder respectively. The 16-bit address generator is generated by cascading four 74HC161 chips into a 16-bit synchronous counter. The counter generates an address for each pulse received. The generated address is sent to the address latch circuit for writing data into the address bits of the SRAM, and is also sent to the sampling logic switching circuit to control the sampling storage depth. [align=center] Figure 3 Schematic diagram of high-speed digital signal acquisition and storage circuit[/align] The data read/write signal decoder is used to generate the read/write and chip select signals of the data storage chip SRAM, as well as the control signals of the storage sampling data logic switching circuit. It is decoded by GAL16V8. The sampling logic switching circuit consists of a dual D flip-flop 74HC74, an 8-bit data comparator 74HC688, and a latch 74HC374, and is used to control the start and stop of sampling. A 74LS688 comparator compares the preset address with the address bits generated by the address generator. If the comparator finds they are equal, it outputs a stop signal. The start signal is generated by controlling the dual D flip-flops. The address latch circuit is mainly used to latch the address of the SRAM in two different states: read and write. When writing to the SRAM, it latches the address generated by the address generator; when reading from the SRAM, it latches the address bits generated by the 8255 in the data transmission and control circuit. Data storage uses two 1MB SRAM chips, HM628128, forming a 16-channel digital signal acquisition system. Generating the SRAM write signal is a challenge. Figure 4 shows the timing logic diagram for generating the write signal, where CLK is the crystal oscillator, Q1, Q2, and Q3 are the 4x, 8x, and 16x frequency multipliers of the crystal oscillator, TC is the counting pulse of the 16-bit address generator, MWR is the data sampling request signal, and RAMWR is the SRAM write signal. The logical expression is: !RAMWR = (!Q3 & Q2) & !MWR. [align=center]Figure 4 SRAM Write Signal Timing Logic Diagram[/align] The logic switching circuit for storing sampled data mainly performs the data bus switching function for reading and writing SRAM. When acquiring data, it switches to the data input terminal using a bus transceiver; when reading data from SRAM, it switches to the data bus terminal of the data transceiver and control circuit so that the computer can read the sampled data from the memory. 2.3 I/O Interface Circuit and Contactor Power Supply Circuit The data acquisition and detection system needs to provide various voltage values ​​within the rated voltage range to the AC contactor coil during dynamic engagement, engagement, and release experiments, and switches the voltage according to the experimental items during automatic detection. The I/O signal from the data acquisition and storage circuit is used as the control signal for the contactor power supply circuit after passing through an opto-isolation circuit. 3 System Software and Design Overview The main function of the system software is to provide users with a good operating environment and respond to user commands promptly. The entire software structure is shown in Figure 5, consisting of a user interface, hardware driver, and data management. [align=center]Figure 5 Software System Composition[/align] LabVIEW (Laboratory of Virtual Instruments Engineering Workbench) is a 32-bit standard virtual instrument development platform launched by National Instruments (NI). It is a graphical programming environment specifically designed for data and instrument control, data analysis, and data representation, and is a new programming method based on a graphical programming language (G-Language). It has a wide variety of powerful function libraries, including data acquisition, GPIB, instrument control, data analysis, signal processing, data display, and data storage functions. It also provides a powerful mathematical analysis library covering many scientific fields such as statistics, estimation, regression analysis, linear algebra, signal generation algorithms, time-domain and frequency-domain algorithms. Therefore, it has been widely used in many fields, including aerospace, communications, automotive, and medicine. In software system design, LabVIEW's powerful graphical programming is used to quickly build user interfaces and test, measurement, and control applications. However, LabVIEW also has shortcomings, such as its inability to handle large amounts of data and its limited ability to implement low-level operations. To this end, a driver program for accessing the hardware device was written in the Visual C++ environment and assembled into a dynamic link library (DLL) function for use by the LabVIEW graphical programming language. For data management, the database software SQL Server and LabVIEW programming interface each other to exchange data, completing functions such as data storage, querying, retrieval, report generation, and printing. 4. Data Acquisition System Experiment The data acquisition and testing equipment was used to perform dynamic engagement process experiments, engagement experiments, and release experiments on the AC contactor. The software's sub-test interface is shown in Figure 6. Experimental parameters can be set in this interface to perform various experiments. [align=center] Figure 6 Data Acquisition Sub-Test Interface[/align] The dynamic engagement process experiment tests the closing sequence of each contactor contact. When the contactor is energized and engaged, the contact state is sampled synchronously, and the actual bounce and engagement time of each contact are analyzed and compared. When used as a production testing device, the closing sequence and minimum time difference of each contact can be set to determine whether the contactor is qualified. The contactor engagement and release experiments verify the working state under different contactor coil supply voltages. Utilizing the powerful data processing and display capabilities of LabVIEW software, a contactor contact waveform display was designed on the user interface. Figure 7 shows a set of data waveforms from the dynamic engagement process experiment. The contact sequence and bounce process can be clearly observed in this waveform. [align=center]Figure 7 Dynamic Engagement Process Experiment Waveforms[/align] 5 Conclusion Bus-based data acquisition and storage systems have advantages such as reliability, ease of implementation, and economy, and have been widely used. The data acquisition card, designed through experiments and exploration, forms a low-cost hardware platform with the existing ISA bus computer system. The software system was developed using the powerful graphical development environment of LabVIEW and hardware drivers written in VC++, realizing real-time sampling of high-speed transient signals and performing data analysis and processing on the AC contactor contact engagement process. The author's innovation lies in proposing the use of contact bounce changes during contact and the time difference between contact engagement as technical indicators to verify the reliability of contactor operation. References: [1] Fei Hongjun, Zhang Guansheng. Dynamic Analysis and Calculation of Electromagnetic Mechanisms [M]. Beijing: Machinery Industry Press, 1993. [2] Li Xingwen, Chen Degui, Sun Zhiqiang, Li Zhipeng, Niu Chunping. Numerical Analysis and Experimental Study on Dynamic Process and Contact Bounce of AC Contactor [J]. Proceedings of the CSEE, 2004, (09). [3] Zhou Weilin, Li Qingfeng, Yang Huayong. Driver of AC1077 Data Acquisition Card Based on LabVIEW. Microcomputer Information, 2006, (01). [4] Zhang Liping, Miao Xiren, Lin Subin. Virtual Testing Technology of Electrical Appliances Based on LabVIEW. Journal of Fuzhou University (Natural Science Edition), 2005, (04).