Development and design of circuit test system based on PXI and GPIB bus

Traditional circuit performance testing uses manual testing to verify whether the circuit is qualified, which has the following main disadvantages: First, during the test process, the connection between the instrument and the object under test is frequently changed, and the instrument is operated continuously to complete the entire test process. Subsequently, manual data statistical analysis and writing of test reports are required, which consumes a lot of time and cannot meet the rapid support needs of military weapons and equipment; second, this traditional testing method does not have automated operation, and is highly dependent on testers during the test process. Testers are required to master the test process proficiently, and human errors are inevitably introduced during the test and subsequent data processing; third, since circuits usually need to complete multiple project tests, the test process is extremely cumbersome and boring, with high labor intensity, and frequent operations and misoperations can easily damage expensive instruments.

An automated test system (ATS) is a system in which the test instrument, under the control of a computer, provides stimulus to the object under test in a certain timing and sequence, and measures the response of the object under the stimulus. GPIB, VXI, and PXI are the most commonly used standard buses for automatic test systems. The comparison of test platforms built by these buses is shown in Table 1. The emergence of VXI in the 1980s brought high-end measurement and test application equipment into the modular stage. The price of VXI is relatively high. With the development of technology, PXI continues the spirit of modularization and provides a new choice for measurement and test equipment with a more compact architecture design, faster bus speed, and lower price. GPIB is a bus protocol for communication between controllers and programmable instruments, also known as the IEEE2488 standard. It is widely used because of its simple use and high transmission rate. With the improvement of the IEEE488 standard, the transmission rate of the GPIB bus has increased and the cost of instruments with GPIB interfaces has continued to decline. PXI and GPIB are currently widely used test buses in industry. They are stable in performance, easy to operate, flexible in assembly, high in equipment utilization, and low in price, making them suitable for building cost-effective automatic test systems. In addition, the rapid development and continuous improvement of virtual instrument technology and the graphical operation interface of the LabVIEW software platform are very helpful for engineers to quickly master design and programming methods and complete project tasks well and quickly. Therefore, virtual instrument technology has also been widely used in the field of industrial measurement.

Therefore, this paper proposes a PXI plus GPIB bus test system based on LabVIEW platform.

The design idea of ​​the GPIB bus automatic test system is to use the LabVIEW development platform, adopt the software design method of virtual instruments, realize the real-time control of various test instruments by the industrial computer through the GPIB bus interface and the corresponding control circuit, complete the automatic test of various performance indicators of the tested circuit, and give full play to the ability of the industrial computer to automatically analyze and process data. Finally, the data is saved in the form of electronic documents and a test report is generated and printed out.

1 Test system design

1.1 Overall framework design

The test system adopts PXI and GPIB bus interfaces, data acquisition cards and corresponding relay control circuits in hardware design to realize the real-time control of various test instruments by industrial computers. In software design, through the LabVIEW development platform, the software design method of virtual instruments is adopted to organically integrate the hardware resources of industrial computers with the instrument hardware, and the data analysis, display and storage are realized through software, solving the technical problem of realizing database management in LabVIEW.

The testing process should be completed in an automated way.

The automatic test mainly uses the relevant PXI board of NI to complete the detection work under the default setting state. The design idea is to control the connection of the test equipment by controlling the opening and closing of the relay through the digital I/O port. After the required test items are connected, the data acquisition and processing program written by LabVIEW is used to obtain the measurement data, and the measurement results are displayed on the display interface, which is convenient for users to analyze and process and draw corresponding conclusions. Finally, the measurement results are saved in the database, which is convenient for later analysis and writing test reports.

1.2 Signal conditioning unit design

There are multiple differential input signals in the circuit under test. When a signal source is used to generate analog signals, differential conversion is required. The differential conversion circuit is shown in Figure 1.

The analysis is as follows:

Practice has proved that this circuit scheme is feasible.

1.3 Measurement and control equipment hardware

The main equipment used in the automatic test is NI's PXI equipment, using the PXI-1042 chassis and PXI-8196 controller to achieve measurement control. The PXI-8196 controller is an embedded controller with a 2.0 GHz Intel Pentium M760 processor, equipped with dual-channel DDR2 memory, a maximum memory capacity of 2 GB, integrated with 4 USB 2.0 ports, a GPIB interface, as well as serial and parallel ports, pre-installed with the Microsoft Windows XP Professional operating system, and is used in application environments that require a lot of analysis work or system development, such as ATE, military/aerospace, communications, industrial and consumer electronics applications. The data acquisition card uses NI's PXI-6259 data acquisition module, which has 16-bit 1 MS/s (multi-channel), 1.25 MS/s (single channel), 32 SE/16 DI, 48-channel digital I/O timing hardware (≥10 MHz), TTL level, 4-channel 16-bit analog output (2.8 MS/s), and an output range of -10 to +10 V. The arbitrary waveform generator uses NI's PXI-5412, which can provide -6 to +6 V signals and provide sine, square wave and other signals to each signal channel under test. The oscilloscope PXI-5152 has 2 single-ended input channels, each with a real-time sampling rate of 1 GS/s. The dynamic signal analyzer uses NI's PXI-4461, which has 2 differential input channels and 2 analog input channels; the real-time sampling rate of the channel is 204.8 KS/s. This card is used to create a universal dynamic signal analyzer interface for manual measurement.

2 Test System Software Design

2.1 Measurement and control software design tools

The measurement and control software of this system is developed on Visual Basic and LabVIEW software development platforms, and the measurement result data is stored in the SQL database. The software system architecture is shown in Figure 2.

In the PXI measurement and control computer, LabVIEW and various data acquisition and processing modules of NI are used to measure the circuit under test; the GPIB interface is used to communicate with various desktop instruments to obtain automatic or manual measurement results; the ADO interface is used to access the network database, and the data required by various users are continuously submitted to the database during the measurement process, which is convenient for subsequent test information management. It is worth mentioning that whether the operation of each measuring instrument can be synchronized, and whether the order and time of the instrument sending and receiving commands, reading/writing data, and executing instructions can be coordinated will directly affect the reliability of the system, the real-time nature of the test data, and the efficiency of the test system. System synchronization is mainly implemented by software in this system, and appropriate program flows are designed according to the user's service requirements and instrument characteristics.

In order to achieve the versatility of the program, Visual Basic/SQL is selected as a tool for data exchange between the test program and the database to separate the measurement data from the test process. The task of the test process is to read the data of the configuration database according to the test requirements, configure the test instrument, perform corresponding data acquisition, analysis and calculation, and write the results back to the test result database. In the computer, the database is installed, and data management and query software is also attached, and the user is provided with the option of installing other software. In this way, the PXI measurement and control computer will not occupy resources due to the need for database management; in addition, when the PXI measurement and control computer is not enabled, only the general computer is enabled, and the data of the measured board can also be sorted and analyzed. Visual Basic can better connect with the SQL database, query and manage the user's database, and apply Visual Basic in the computer to write data management and query software that facilitates user access to data.

2.2 Measurement and control software structure design

The system's measurement and control software is software running on the PXI measurement and control computer, and its main software hierarchy block diagram is shown in Figure 3. The software adopts a hierarchical structure, and while realizing functional testing, it also has data storage, query and playback functions, and has good practicality and operability.

3 Conclusion

The research and development of this topic is of great significance to the detection of circuits. First, the use of an automated test system greatly improves test efficiency, saves precious time, and can meet the needs of rapid equipment support under information conditions; second, it frees testers from tedious detection tasks, reduces labor intensity, and greatly saves manpower consumption; finally, after the entire test system is connected once, no human intervention is required. You only need to select the test items on the computer and fill in some basic data to start the test. Non-professionals can also complete the test process, which basically eliminates errors caused by human misoperation, improves the credibility of the test results, and ensures the safe use of the system.