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Virtual instrument and experimental platform based on hpi/o library

1 introduction

modern microelectronics technology, computer technology, software technology, network technology and their applications in measuring instruments are highly developed. New theories, new methods, new fields and new instrument structures of test and analysis are constantly emerging, breaking through the concept of traditional instruments, thus establishing a new milestone of electronic measuring instruments virtual instrument. Any instrument consists of three functions: signal acquisition and control, signal analysis and processing, and result expression and output. If we combine computer technology and instrument technology to realize these three functions, and let the computer complete the signal analysis and processing, result expression and input of the instrument, this is virtual instrument

in the virtual instrument system, the concept of "software constitutes an instrument" is emphasized. The hardware is only to solve the signal. It realizes the versatile input and output of the universal experimental machine. The software is the key of the whole instrument. Users can define the functions of the instrument according to their own needs. By modifying the software, it is convenient to change, increase or decrease the functions and scale of the instrument system, and it can be easily connected with peripherals Network and other application connections

2 composition and working mode of virtual instrument

virtual instrument [1] is usually composed of personal computer, modular functional hardware and control software, that is, the signal or data to be measured is collected and transmitted to the computer through modular functional hardware, and then analyzed and processed by the control software and transmitted to the user; At the same time, the virtual platform obtains user instructions through the man-machine interface, and then transmits them to the controlled object through modular functional hardware. The working principle of virtual instrument is shown in Figure 1

Figure 1 working principle diagram of virtual instrument

2.1 modular functional hardware

the measurement and control object has the following interface modes with the computer: signal conditioning instrument, GPIB (general purpose interface bus) instrument, serial port instrument, VXI instrument. Due to the use of programmable instrument amplifier technology, real-time system integration bus technology, double buffer technology of high-speed data acquisition and interrupt DMA and other high-tech technologies, these hardware provide technical support for the data acquisition card, making its performance more flexible and precision higher. Among them, the most widely used control instrument in precision measurement is GPIB interface instrument, that is, general interface bus instrument

therefore, programmable instruments are closely connected with computers through GPIB interface, which makes electronic measurement develop from independent manual operation of a single instrument to the direction of forming a large-scale automatic test system

2.2 control software

using HP i/o library to control GPIB instruments, there are several control libraries: one is using GPIB library. GPIB program library is a general instrument control interface bus standard developed by HP company in the early 1970s. The second is to use visa (Virtual Instrument Software Architecture) library. Visa controls the single interface program library of GPIB and other kinds of instruments on the working platform. The third is to use the SiCl (standard instrument control Library) library. The program developed by SiCl supports HPIB, GPIB, VXI, RS-232 and LAN interfaces. The fourth is to use VXI library. It is based on the programming command set of SCPI library and can be used in many programming environments

according to the type of connected instruments and equipment and the setting of interface card, the above four different program control libraries can be selected. The experimental platform uses HPIB server based on GPIB library to connect the measured object and data acquisition interface

it is also necessary to understand HP-IB (interface bus), namely HP interface bus protocol, for data communication and control program preparation of HP instruments. This protocol is an interface program specially set up for HP standard instruments based on GPIB, so it has more advantages Host: the host is supported by a height adjustable framework (the machine base has strong pertinence and more perfect functions. Users can install HP-IB DDE server through this protocol, and then add instruments through DDE server.

3 GPIB interface connection and the establishment of a switching power supply test experimental platform

the establishment process of the virtual platform is introduced through the example of establishing a switching power supply test platform. The circuit hardware connection is shown in Figure 2.

Figure 2 virtual test platform hardware The AC power supply in the test platform adopts the HP 6813b AC source/analyzer that accelerates the improvement of the green manufacturing standard; The tested switching power supply adopts astec desktop ATX; The electronic load is HP 6050a; The data acquisition card adopts hp-i ball screw with the highest accuracy B 82335 interface card

the working process of the experimental platform is as follows: the AC power supply generates the required AC voltage waveform according to the settings of the application program, adds it to the input end of the measured object, and analyzes the performance indicators of the switching power supply by measuring the changes of voltage and current at the input end. The output end of the switching power supply is connected to the electronic load. Changing the input voltage can also change the settings of the electronic load to test the anti-interference and stability of the switching power supply

after connecting the hardware equipment with GPIB standard connection according to figure 2, install the data transmission software: HPIB DDE server and HP i/o library. Configure the address of HPIB in HPIB library after setting the SiCl name and visa name in the interface card. At this time, the instrument can be controlled remotely, and the basic configuration of the virtual laboratory is established

3.1 graphical user interface GUI

the GUI of the test platform established in this paper mainly includes:

(1) HP AC power supply/analyzer graphical user interface (HP ACsource GUI). Its advantage is mainly to use a fast and simple method to generate a standard or interfering AC source for product testing

(2) HP harmonic