Design of special cable automatic measurement system based on integrated system integrated chip

1 Introduction

In modern armored communication command equipment, equipment with powerful functions, precise control, and reliable operation is composed of more and more electronic extensions and components connected through dense cables, wiring harnesses, and networks.

The correctness and reliability of cable and network connections play an important role in ensuring the reliable operation of the entire electronic system. Automatic testing and inspection of the continuity, insulation and other indicators of complex cables, wire harnesses, and networks is an indispensable link in the cable assembly and production process. Traditional low-voltage, low-current manual and semi-automatic testing is far from meeting the needs of modern high-reliability electronic equipment production.

At present, the cable detection of armored communication command equipment adopts the traditional and backward manual detection method, using three-purpose meters, buzzers and homemade simple test benches to detect continuity. Manual inspection methods have many shortcomings that cannot be overcome, and they can no longer meet the requirements for large-volume, high-precision, and high-reliability cable inspection:

(1) 1 or 2 people cooperate in point-by-point inspection, which is inefficient, slow, heavy workload, precise, tedious, boring, and easy to fatigue. It is necessary to compare drawings, wiring tables, and core wire numbers, which can easily lead to missed inspections and errors. Check.

(2) It can only detect paths and cannot detect short circuits (i.e. wrong connections or multiple connections) in dozens of core cables.

(3) Generally, only continuity is detected, and on-resistance is not detected. Poor and unreliable contacts cannot be detected.

Based on the above reasons, there is an urgent need to develop a special testing equipment that can automatically test the cables of the most armored communication command equipment.

2 System design principles

The system structure is shown in Figure 1.

The functions of each functional block are as follows:

2.1 PC

The main function of the PC is the built-in "cable management system", including: cable models and specifications, socket model specifications, cable type spectrum, etc., as well as functions such as storage and analysis of test results.

2.2 Host

The host computer stores the type spectrum of the cable under test downloaded from the "cable management system" through the serial port. Up to 150 types of cable type spectrum can be stored. It does not need to be connected to a PC during testing. The display mode uses a 320×240 wide-temperature LCD. display. During the test, the host computer sends test commands to the slave computer via wireless according to the type spectrum of the selected cable under test, and the host computer and the slave computer cooperate in real time to complete the measurement.

2.3 Slave machine

The slave machine is composed of a programmable switch matrix and a load, and receives test commands from the host machine.

2.4 Cable-specific conversion connector

The cable-specific conversion joint is used to connect the cable under test to the host and slave machines respectively to complete the measurement. Each type of cable under test requires a customized pair of conversion joints.

3 Hardware system on the system platform

The host consists of a main control unit, a transceiver unit, a switch matrix, a display and keyboard, a power supply, etc. Its structure is shown in Figure 2.

3.1 Introduction to LH79520

LH79520 is an integrated system integrated chip (SoC) based on the 32-bit ARM7 core. It includes a 32-bit ARM7TDMI RISC processor core designed by ARM, Cache RAM, a write buffer and storage management unit. It has the characteristics of low power consumption and high performance.

3.2 Display control board block diagram

The block diagram of the display control board is shown in Figure 3.

The display and keyboard control system consists of CPU, display, keyboard, RS 232 interface and data exchange. The CPU is LH79520. In order to meet the need to store some data, a 32 kB E2PROM is used as a data memory to store some test results. The display part uses OKI's MSM6255 as the display controller, and an external 32 kB RAM is used as the memory for display data. The horizontal synchronization signal, field synchronization signal, and display data generated by MSM6255 are sent to the EL display screen. The keyboard part uses 8279 as the keyboard controller. In order to realize the control of the instrument by an external computer, the factory MAX202 is used as the interface level conversion control in the system, and the RS 232 interface is used to connect to the outside.

3.3 Slave block diagram

The slave machine block diagram is shown in Figure 4. The transceiver module is composed of nrf401 single-chip transceiver module as the core and peripheral circuits. The operating frequency is 133.92 MHz, the modulation method is FSK, and the maximum transmission rate is 20 kb/s. Built-in antenna, maximum straight-line transmission distance is 100 m.

4 Software systems on system platforms

4.1 Design of continuity test algorithm

4.1.1 Establish port relationship matrix

The port relationship matrix design is shown in Table 1.

Note: (1) This matrix is ​​used to describe the correspondence between cores and ports;

(2) N=61:

(3) This matrix corresponds to the cable type spectrum;

(4) The upper triangular array is valid, including the diagonal;

(5) 0: means not connected; 1: means connected; X: means invalid.

4.1.2 Establish cable relationship matrix

Note: (1) This matrix is ​​used for short circuit judgment (the results are written in Table 2) and partial path judgment (the results are written in Table 3);

(2) M is the maximum number of cores of the cable (2≤M≤61);

(3) The upper triangular array is valid, excluding diagonals;

(4) 0: Indicates invalid;

(5) X is initially 0; X=3 is short; X=4 measurement fails (wireless communication error).

4.1.3 Short circuit measurement

Starting from the first row of the cable relationship matrix, scan the upper triangular matrix row by row.

During the measurement process, if the result is short circuit, set X=3; if the result is measurement failure, set X=4 and continue.

During the scanning measurement process, if the result is pass, the core numbers in the two pass cores LX and HY will be converted to the column numbers of the reference measurement list.

Baseline Measurement List (Table 3) Column Number:

[LX]=LX;[LY]=HY

Set the status X=1 of the reference measurement list column numbers [LX] and [LY], and continue to scan the upper triangular array line by line with X=1.

Reference core definition: One of any two cores measured to be connected is the reference core.

This list is used to store the pass and break results.

X is initially 0; X=1 is connected; X=2 is disconnected;

Scan table 3 to find the reference core. If all Xs are 0, all cables are broken; if

Use the reference core to judge the core whose X is 0 in Table 3. If it is connected, set X=1; if it is broken, set X=2; if the measurement fails, set X=4.

4.1.4 Processing flow of cable continuity measurement

5 Conclusion

The continuity meter can automatically measure special cables within 2 to 60 cores. The main features are:

(1) Automatically and quickly test cable continuity. The 750 points/s test speed enables complex cables with dozens of cores to complete continuity detection in a few seconds.

(2) Automatically group and arrange short circuit tests to detect all possible short circuit errors (i.e. wrong connections, multiple connections).

(3) The program controls the automatic testing process and can detect cables multiple times at any time, which facilitates quality management and greatly improves work efficiency.

(4) Detect small changes in contact resistance, and detect quality hazards such as poor contact, broken wire cores, and missing connections in parallel lines.

(5) Easy to use. It only requires one person to operate, has a friendly human-machine interface, is a handheld detection device, and has ultra-low power consumption.

(6) It can store 512 types of cable type spectra. The type latent input can be downloaded from the PC through the communication interface. The measurement results can be stored and transmitted to the management system.