Design of Universal Oscilloscope Automatic Test System

1. Introduction

With the development of electronic science and technology, oscilloscopes have become one of the indispensable tools for electronic technicians. Due to the influence of various factors such as drift and aging of components, if the accuracy of the oscilloscope is to be guaranteed during use, it must be calibrated regularly. In the past, traditional calibration methods were all manual operations. Due to the wide range of detection and multiple functions, calibration is often very busy. Not only is the labor intensity high, the work efficiency is low, but the calibration data is also difficult to manage. For this reason, automated testing of oscilloscopes is an urgent and imperative task.

To realize the automation of oscilloscope calibration, the interface problem must be solved so that the instrument controller and the instrument can communicate with each other. To this end, in this system, a GPIB interface board (ie, IEEE-488 interface board) is inserted into the I/O channel of the microcomputer to realize the communication between the computer and the oscilloscope calibrator (including the transmission of program control commands, measurement data, and instrument status information). This system can complete the acquisition, testing, and data error analysis of various parameters of the oscilloscope, and complete the display, storage, review, and output printing of measurement results.

2. Introduction to GPIB Interface Board

The uPD7210 universal interface chip is the core of the GPIB interface board. Its 40 pins are mainly divided into two parts. The first part is connected to the microcomputer bus, that is, directly or through some auxiliary circuits, connected to the I/O channel of the microcomputer. For example, it is connected to the data bus, address bus, clock, read and write interrupt request, DMA request and DMA enable signal lines. The second part is directly connected to the GPIB bus through the bus transceiver. In addition, there are three transmit and receive control lines T/R1-T/R3, which are used for input and output control and to indicate certain working states of the interface function.
There are 10 interface functions in the GPIB system, namely:
1) Talk function (T function)
2) Listen function (L function)
3) Source interlocking communication function (SH function)
4) Receiver interlocking communication function (AH function)
5) System control function (C function)
6) Service request function (SR function)
7) Parallel query function (PP function)
8) Remote/local function (R/L function)
9) Device clearing function (DC function)
10) Device triggering function (DT function)
When running, first initialize 8 write registers and 8 read registers, and then issue commands to the devices on the GPIB bus through the data output register to transmit data. By reading certain status registers, you can understand the required status, and you can also read back the data sent by the device on the GPIB bus through the data input register. The entire communication process is controlled by the program to achieve the purpose of automatic detection.

3. Establishment of automatic detection system

1. Hardware composition of the system

The automatic detection system is composed of an AST286 microcomputer with a GPIB interface board, a program-controlled oscilloscope calibrator and a 24-pin printer.

The GPIB interface standard stipulates that the listening address of the instrument (calibrator) is 01L5L4L3L2L1, and the speaking address is 10T5T4T3T2T1. When the lower 5 bits of the address sent by the controller (microcomputer) match the device address of the calibrator, the calibrator is addressed as a listener or speaker. The device address can be set by toggling the 5-bit address switch on the instrument panel. The device address of the controller is set by writing the address to the address input/output register 6W through the initialization program. Its structure diagram is as follows:

Figure 1 System hardware structure diagram

2. System software compilation

Based on the principle of convenience, versatility and reliable operation, the user interface of this test system adopts Chinese characters for display and menu selection, so that the operator can use it without mastering too many computer languages. At the same time, the software is compiled in full accordance with the oscilloscope verification regulations promulgated by the state. It can not only test, display, print and review various parameters of the oscilloscope, but also has a memory function, that is, after verifying a certain model of oscilloscope, when testing the same model of oscilloscope again, it can directly test according to the previously set range and parameters without having to repeatedly answer the computer's questions.

In order to improve the reliability of the software and the accuracy of detection, this system adopts a modular and structured design concept. Modularity enables each parameter detection subroutine to be completed independently without being affected by other modules. This method makes the program have good security and reliability during debugging and operation. In addition, the structured sequential execution and its judgment function make it fully consider various possible situations in program design, and can handle some problems that arise in the detection by itself, thus ensuring the integrity of the program to a certain extent. The flowchart of the software is as follows:

Figure 2 System software flow chart

When the user enters the model of the oscilloscope, a query menu will appear, allowing the user to enter the number of the oscilloscope being tested, the inspection unit and other related information. When the user tests a certain range of the oscilloscope, it can automatically determine whether its measured value is out of tolerance. If it is within the error range, it will record its measured value, otherwise, it will display that this range is out of tolerance. In the printing program, it is divided into two parts, one is the header part of the test report, and the other is the test data. The header part is stored in the disk as a separate file, and the data is stored in another file as original data. The purpose of this is to facilitate computer management in the future. In addition, for the convenience of user operation, this system also has the function of displaying and reviewing data.

IV. Conclusion

Computer manufacturing technology and application technology are constantly developing, various oscilloscopes with interfaces will be widely used, and their verification technology will reach a new level. As the verification work needs it, we will make it more perfect.

References

[1] Sun Xu, Automatic Detection System and Programmable Instrument, Electronic Industry Press
[2] Gao Dengfang, Practical Measurement and Control Interface Technology of Microcomputer, Beijing Science and Technology Press
[3] Gao Guangrun, Application of Microprocessor in Electrical Measurement Technology, Machinery Industry Press