Abstract: To address the shortcomings of traditional RLC parameter measuring instruments, this paper proposes an improved virtual RLC parameter automatic measurement system using computer hardware resources and the graphical programming language LabVIEW. The basic block diagram and software design method of the measurement system are introduced, with a focus on the design of the RLC component parameter measurement board based on the PCI bus. This automatic RLC parameter measurement system features automatic range switching by the PC during measurement, achieving intelligent measurement. Keywords: Virtual Instrument, PCI bus, LabWindows/CVI, CPLD [b][align=center]The Automatic Measurement System of RLC Parameter based on Virtual Instrument SUN Hong-bing[/align][/b] Abstract: By improving the performance of the traditional RLC parameter measurement system, an RLC parameter automatic measurement system is designed using computer hardware and LABVIEW. The design method of the hardware and the software of the system are presented. And the design method of the RLC parameter measurement card based on PCI is introduced. The RLC automatic measurement system can shift gears automatically by computer and has realized the intellectualization of the measuring appliance. Keywords: Virtual Instrument, PCI bus, LabWindows/CVI, CPLD 1. Introduction: RLC component parameter measuring instruments are used to measure lumped parameters such as resistance R, inductance L, mutual inductance M, capacitance C, and quality factor Q. Traditional RLC parameter measuring instruments, such as various AC bridges, require manual adjustment of ranges when measuring the parameters of components such as resistors, inductors, and bridges. Technicians rely on observing the balance of the bridge to determine the parameters of the R, L, C components being measured. This requires repeated adjustments, and the measurement accuracy is influenced by human factors, resulting in significant errors. With the development of computer technology and the continuous advancement of instrument technology, instruments are gradually developing towards intelligence, automation, and virtualization. Automatic RLC testing instruments exist abroad, but they are large and expensive [1,2]. This paper designs an automatic RLC component parameter measurement system based on the PCI bus using CPLD chips and PCI interface chips. LabWindows/CVI is used as the software development platform, making the system small, inexpensive, easy to upgrade, and with a good human-machine interface. 2. Measurement Principle There are three main methods for measuring the parameters of components such as resistors, inductors, and bridges: the bridge method, the resonance method, and the volt-ampere method. The bridge method and the resonance method mainly utilize the deviation measurement principle, requiring repeated adjustments by technicians, making automatic measurement difficult. The volt-ampere method is derived from the definition of impedance. That is, if the vector current flowing through the impedance to be measured is known and the voltage across the impedance to be measured is measured, the vector of the impedance to be measured can be obtained by the ratio. Obviously, to realize this method, it is necessary to use a computer to perform vector measurement and division operation. There are two types of volt-ampere method: fixed axis method and free axis method. The fixed axis method has high hardware requirements and in-phase error, so it is rarely used. The free axis method has been widely used in RLC component parameter measurement with the help of a computer. The principle of RLC parameter measurement by the free axis method is shown in Figure 1. The relationship between the voltage Ux across the impedance ZX to be measured and the voltage Us across the standard impedance ZS can be represented by Figure 2. It can be seen that as long as the two projection values ​​of UX and US on the rectangular coordinate axis are measured respectively, the impedance ZX to be measured can be obtained by equation (1) [2]. [align=center] Figure 1 Schematic diagram of measurement principle[/align] (1) In the formula, e is the scale coefficient of the A/D converter, that is, the voltage value represented by each number; Ni is the digital quantity corresponding to Ui (i=1,2,3,4), where Ni is obtained by Ui through the integrating A/D converter, and ZS generally adopts the standard resistor RS. 3. Hardware design of measurement system According to the above principle, the block diagram of the designed automatic measurement system for RLC parameters is shown in Figure 1. All parts except the computer are on a board. This is an RLC element parameter measurement board based on PCI bus, which mainly consists of PCI interface circuit, A/D conversion circuit, sine signal generator, reference phase generator and phase detection circuit. [align=center] Figure 2 Block diagram of measurement system principle[/align] 3.1 Design of PCI interface circuit The PCI bus is the interconnection structure between the processor/memory on the microcomputer and the peripheral control components and peripheral add-on cards. Considering the complexity of the component parameter measurement and control logic and leaving room for future functional additions, the main device interface chip PLX9054 was selected. It integrates a PCI interface chip (9054), an SDRAM controller, and a RISC CPU. This allows for rapid conversion from designs based on other buses (such as ISA) to PCI bus-based designs, and also accelerates PCI bus-based system design, greatly facilitating instrument virtualization and integration. Simultaneously, the isp2128 chip is used to implement a frequency divider, a counter (used to generate address signals for each ROM), and other control functions. The designed circuit is shown in Figure 3. [align=center] Figure 3 PCI9054 and Local Bus Interface[/align] 3.2 Sine Wave Signal Generator and Phase Detector Circuit Design As the measurement principle shows, the instrument's operating frequency directly affects the measurement accuracy. Therefore, the test signal source frequency accuracy, spectral purity, and amplitude stability must be high. The phase detector circuit also requires strict synchronization between the signal source frequency and the phase reference signal frequency. Therefore, the sine wave signal source and the reference phase generator are closely related in the circuit. Currently, signal source circuits mostly employ DDS technology. First, a sine curve sampling point for one cycle is generated using digital synthesis and stored in a ROM (sine ROM in Figure 2). The relationship between the sample data stored in each memory cell and its address is consistent with the relationship between the time axis and the sine amplitude of the sine wave. Thus, by sequentially reading the sample data from the ROM cell by cell, a quantized sine curve can be obtained. If this process is repeated periodically, and the output is after D/A conversion and smoothing filtering, a continuous sine signal can be obtained. The generation principle of the phase reference is the same as that of the signal. The data used to generate the reference phase signal is stored in a reference phase ROM (as shown in Figure 2). The difference between the reference phase ROM and the sine ROM is that the reference phase ROM does not store a single sine sampling point value for one cycle, but rather four sets of sine signal sampling values ​​with phase differences of 90°. It uses six-channel addressing, and the output signal is sent to a multiplicative D/A converter. The measured signal is applied to the reference voltage VREF terminal. In this way, a reference phase signal of the same frequency is generated simultaneously with the test signal. Inside the D/A converter, digital full-wave phase detection is achieved by multiplying the reference phase signal and the measured signal. 3.3 Control Section and System Working Process The logic control completed in the design can be divided into three parts: test signal generation function section, data generation section and logic control section. The control logic is completed by ISP2128. ISP2128 is a programmable logic device from LATTICE, with 128 registers and 6000 PLD gates. The design adopts a mixed approach of schematic diagram and VHDL language to divide the functions to be implemented into several sub-modules. Each sub-module is implemented by VHDL language programming, and then they are synthesized by schematic diagram to realize the design function. The operator selects the frequency of the test signal and switches the gear through the computer. In this way, the data exchange between the board and the computer is divided into three parts: (1) The signal used to control the test signal is sent from the computer to the board. (2) The data obtained by the board in one measurement is sent from the board to the computer. (3) Handshake signal used for data transmission between the board and the computer. The PCI9054 works as follows: A control signal is sent to the measurement circuit, which then begins measurement upon receiving the signal. Each measured result generates an interrupt on the PCI bus via the PCI9054. The computer responds to the interrupt and reads the measurement result through the PCI9054. This process continues until all eight sets of test data are sent to the computer, completing one measurement cycle. The data read by the computer is Ni, and the required parameters such as R, L, C, and Q can be calculated using the application program. 4. System Software Design After the hardware design of the measurement system is completed, the corresponding PCI board driver and measurement application program need to be developed. 4.1 Driver Design The driver program establishes data and command transmission between the computer and the board. The PCI board driver program is developed using DDK and DriverStudio. Following the setup wizard, first select the WDM option, then select the PCI bus type, and assign an interrupt number and memory object to the board. The specific memory location and interrupt number do not need to be specified, as in plug-and-play drivers, the specific memory location and interrupt number are allocated by the operating system during system startup. The memory range is set in the configuration registers on the measurement board [3,4]. After completing the wizard setup step by step, the basic framework of the driver is generated, including: memory object, interrupt object, interrupt handling routine, read/write routine, etc. The read/write routine is the routine of the device driver to handle the user's read and write requests, and is the core of the driver. It is used to respond to the user's read/write requests, write data to the user buffer, and perform other controls. The read/write routine is written using a technique commonly used in device drivers—serialized I/O requests. 4.2 Application Design The LabWindows/CVI is selected as the main development platform for system development. This is a virtual instrument development environment based on standard C language developed by NI, which has a good user interface [5]. The system software adopts a modular design, mainly including user interface design (instrument soft panel), application and driver interface, data reading and processing, result output and display, etc. The system operation interface (instrument soft panel) is the main way of human-computer interaction. A good operation interface can make it convenient and intuitive for users to operate the measurement system and obtain measurement results in a timely manner through the interface [6]. The operation interface designed in this system is shown in Figure 4. To enable LabWindows to access the board during software development, the interface between LabWindows and the device driver must first be established. This requires importing the Setupapi.h and Setupapi.lib files from the DDK into the project. The data reading and processing section uses buttons on the panel to select the measurement frequency, component properties, and range, calling different functions to calculate the read data and display the results on the instrument panel. [align=center]Figure 4 Virtual Panel[/align] 5 Conclusion The RLC component parameter measurement system designed in this paper simplifies the PCI bus design by using the PCI9054 interface chip. Simultaneously, the signal generation and control sections are all housed within the CPLD chip ISP2128, saving board space and improving signal source quality. Furthermore, the use of the LabWindows virtual instrument development software enhances the system's signal processing capabilities and facilitates future system upgrades. The measurement system developed using these measures has advantages such as high automation and intelligence, low development cost, and short development cycle, enabling real-time online measurement of RLC component parameters. The use of virtual instruments to gradually replace traditional instruments has become a trend in the testing field. In practical applications, program optimization and hardware/software integration should be performed according to specific circumstances to enable virtual instruments to achieve higher performance. The innovations of this paper lie in its adoption of advanced measurement principles and the design of a PCI interface circuit using the PCI9054 chip. The CPLD chip ISP2128 is used to generate frequency division signals and control signals for related functional modules. This unique design method effectively simplifies circuit design, improves reliability, and allows for long-term measurement without the need for specialized calibration. References [1] Li Guishan, Qi Dehu. PCI Local Bus Development Guide [M]. Xi'an University of Electronic Science and Technology Press, 1997, Xi'an, 13-20 [2] Li Nianqiang, Jing Yazhi. Research on a new type of RLC digital bridge. 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