System hardware design:
Compared with GPIB, VXI, RS232 and other instruments, PXI modular instruments have the advantages of fast speed, small size, and easy expansion. Therefore, PXI modular instruments are mainly used in hardware, and conventional signal sources (SOURCE) and signal measurement are selected. Module (SENSOR), expand special and self-developed equipment through GPIB and RS232 bus. The system hardware schematic diagram is shown in Figure 1.
Due to the large number of PXI modules, and for future expansion, the 18-slot PXI-1045 chassis was selected; in order to further improve the integration of the system platform, the PXI-8187 zero-slot embedded controller was selected, eliminating the use of MXI in the previous system -2 The way of using the industrial computer as the main controller, PXI-8187 has a GPIB interface, which can easily expand the GPIB bus equipment. Some instrument resources and components require serial communication, so PXI-8421 is used to expand 4 serial ports.
Signal acquisition
6 1/2 digital multimeter PXI-4070 and 5 1/2 digital multimeter PXI-4060 are commonly used test modules for measuring voltage, resistance and current. They can measure 0-300V voltage and 0-1A current. 0-100M ohm resistance;
Oscilloscope PXI-5112 (2 channels 8 bits
Resolution, 100MHz bandwidth) and analog input PXI-6070E (16 single-ended input / 8 differential input, 12-bit resolution, 1.25M sampling rate), can meet the commonly used continuous wave and single-point voltage signal acquisition When PXI-6070E performs data acquisition, two SCXI-1125 are connected to the front end for signal conditioning (10Khz or 4Hz low-pass filtering and attenuation). PXI-6070E is also used for communication between the controller and the SCXI chassis.
The high-speed DIO PXI-6534 can collect and output high- and low-speed discrete quantities. Special and complex signals are collected and processed using GPIB equipment and RS232 self-developed equipment, such as a spectrum analyzer.
2. Signal output
Function generator PXI-5421 (16-bit resolution, 100MS / s sampling rate, bandwidth 43MHz) and high-speed analog output PXI-6733 (8-channel output, 16-bit resolution, update rate 1MHz) can be used together Wave and single point voltage signal output; SCXI-1124 is used to isolate the output of analog voltage and current.
Special and complex signal output adopts GPIB equipment and RS232 self-developed equipment, such as AC and DC power supply, RF signal source, atmospheric data test system, simulator, etc.
3. Signal routing
Since most airborne electronic devices have a large number of signals, it is impossible to directly connect all signals to resources at the same time. It must be switched through the relay matrix. The relay must have a fast enough response time to switch on and off large signals, so we Two relay matrix modules SCXI-1129 and accessories SCXI-1333 and SCXI-1339 are selected to form a suitable relay matrix (maximum on-off capacity 150VDC / 1A, 150Vrms / 250mA). In the process of signal connection and disconnection, in order to realize the automatic selection of the optimal path and safety protection (to avoid the source connection), we re-programmed the relay matrix driver, and achieved satisfactory results in actual use.
4. Resource interface and adapter
A resource interface is a collection of all resource interfaces, and each component connects some resources through an adapter as needed. One or more UUTs share an adapter, so the test system can be configured with one or more adapters based on the signal condition of the UUT.
System software design:
CVI is a virtual instrument development software that adds instrument control and tool function library on the basis of standard C language (ansi C), provides many practical routines, has a friendly graphical user interface, and C language is familiar And easy-to-use development environment, so the use of CVI can speed up the development of test procedures (TP). The system software principle is shown in Figure 2.
In order to facilitate and standardize the writing of TP, the TP development management software automatically generates the test program code framework and instrument operation code based on the input test information. After the test program is written, it compiles and generates a dynamic library. The test program executes the management software to call and manage the test program.
During the development of the test program, instrument operation and virtual instrument interface development are two key points.
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