Aircraft electrical parameter comprehensive test system based on ADLINK DAQ-2204

For aircraft electrical systems, their electrical parameters need to be tested during their production and maintenance. However, due to the diversity of aircraft electrical parameters, a variety of measuring instruments and meters are required when testing a certain electrical system, which increases the investment in test equipment and the complexity of the test work. Therefore, it is necessary to use a multifunctional aircraft electrical parameter test system.

1. Introduction to the functions of the test system

The aircraft electrical parameter comprehensive test system is a set of special test equipment developed according to the needs of aircraft electrical system design and inspection. It is mainly used for electrical characteristic parameter testing of electrical systems and products such as aircraft power supply systems, static converters, transformer rectifiers and transformers during ground tests to evaluate whether the electrical characteristics of the tested objects meet the requirements of relevant national military standards and design specifications.

The test system is mainly based on ADLINK's DAQ-2204 multi-function acquisition card, and combined with virtual instrument technology, it can not only measure some parameters that require special data acquisition and analysis methods specified in the national military standard GJB181-1986 and the latest revised GJB181A, but also record waveforms of multiple channels in real time, and can replace the functions of instruments such as oscilloscopes, multimeters and spectrum analyzers during ground experiments on aircraft electrical systems; this test system can also play back recorded historical data, and can automatically generate and print test reports and test result curve comparison charts in accordance with the requirements of the national military standard. In addition, the digital I/O on the acquisition card is used to realize the load loading and unloading control and the synchronous testing of parameters.

In order to share test data with other analysis systems, the system is also connected to the local area network.

2. Characteristics of aircraft electrical parameter testing

For existing military and civil aviation electrical systems, although the tests of their core components are different (mainly the differences in excitation source, excitation position and timing, and test points), the inherent detection essence is the same: add an excitation to the system under test at a certain time and position, then obtain the corresponding system information from the appropriate time and position, and finally calculate the various performance parameter values ​​of the electrical system through analysis software, so as to make a corresponding evaluation of the performance of the system under test.

3 Hardware Implementation Principle

The hardware part of the test system is mainly composed of an industrial computer, a PCI data acquisition card, a signal conditioning circuit, a sensor, and a printer, as shown in Figure 1.

Figure 1. Schematic diagram of the electrical parameter comprehensive test system

3.1 Data acquisition card and industrial computer

PCI data acquisition card are the core parts of the test system. The system uses ADLINK's multi-function data acquisition card DAQ-2204, which has 64 single-ended or 32 differential analog input channels, and its single-channel maximum sampling frequency is 3MS/s, with 12-bit resolution. DAQ-2204 obtains the sampling data of each channel by scanning. When scanning the signals of 12 differential channels, it can ensure that the sampling frequency of each channel is above 100kS/s, thus ensuring the steady-state parameter test in accordance with the requirements of the national military standard GJB181. Another reason for choosing DAQ-2204 as the acquisition card is that it is equipped with a synchronous digital input port (SDI). The lower 4 bits of the DAQ-2204 sampling data are the SDI input bits. By obtaining the trigger and timing signals of the conditioning board through SDI, transient parameter testing and steady-state surge voltage analysis can be easily realized. In addition, the 24-channel general digital I/O of DAQ-2204 is used to realize the software loading and unloading of electrical loads, thereby increasing the control function of the system. All these performances guarantee the transient conversion characteristics and various steady-state and transient tests in accordance with the national military standard GJB-181.

In view of the large electromagnetic interference at the electrical system test site, and to ensure that the system has good real-time data acquisition and rapid analysis capabilities, the system selected a high-end industrial computer as the main controller.

3.2 Sensors and signal conditioning

The signals to be tested in this test system include various voltage and current signals of the aircraft electrical system. Among them, the voltage signal directly enters the conditioning box, and enters the test system after being divided by precision resistors; the current signal is first converted into a voltage signal by the LEM sensor, and then sampled by precision resistors before entering the test system. Due to the special requirements for the testing of three parameters including AC and DC voltage distortion and the DC component of AC voltage, the corresponding conditioning circuit is specially designed in this test system to improve the bandwidth and dynamic performance of the system, thereby improving the comprehensive testing capability of the entire system.

4 Software Design Solution

As a comprehensive electrical parameter test system, the system has strict requirements on the analysis software. It not only requires the software to run stably, but also must have complete functions, high execution efficiency and convenient data management. Therefore, the application software development platform of this system chose LabVIEW7, a graphical development software with a high reputation in the measurement and control industry, and used virtual instrument technology to implement the entire measurement and analysis software. LabVIEW7 is an efficient graphical development environment that integrates simple and easy-to-use graphical development methods, flexible and powerful programming languages ​​and rich data analysis modules, which can greatly shorten the development cycle and improve software quality.

When users purchase DAQ-2204, ADLINK provides a driver software package for the LabVIEW development platform, D2K-LVIEW, with the board. It ensures that users can implement a fully functional test system software module through simple design without developing the underlying driver of the board. With the support of D2K-LVIEW, when designing measurement and control software based on LabVIEW, it is not necessary to spend a lot of time to develop the corresponding board driver. Users can use ADLINK products as conveniently as using NI products.

The test analysis software is divided into two parts according to the different test contents: parameter test specified by the national military standard GJB181-1986 and parameter test specified by the national military standard GJB181A. The first part is divided into several sub-modules according to the different test contents, including: test channel parameter setting module, three-phase AC steady-state voltage analysis module, AC voltage modulation analysis module, AC steady-state surge voltage analysis module, frequency analysis module, DC steady-state voltage analysis module, power and power factor measurement module and excitation parameter test module; the GJB181A part includes AC distortion test module and DC distortion test module, etc. Each test module is uniformly scheduled by the main control module, and all realize the functions of test data storage, playback and test report generation and printing.

Figures 2 and 3 are the software structure diagram of the electrical parameter comprehensive test system and the three-phase AC steady-state voltage analysis interface, respectively.

Figure 2. Software structure diagram of the electrical parameter comprehensive test system

Figure 3. Three-phase AC steady-state voltage analysis interface

5 Conclusion

The aircraft electrical parameter comprehensive test system is specially developed according to the characteristics of aviation electrical systems. It is mainly used for inspection and testing of aircraft electrical systems during production and maintenance. The measurement accuracy of AC and DC steady-state voltage and phase shift reaches 0.2%, the transient test accuracy also reaches 0.5%, and the frequency accuracy is 0.02%, which fully meets the test requirements of the national military standards GJB181-1986 and GJB181A. It has been adopted by many aviation electrical system manufacturers and research institutes with satisfactory results.

References:
[1] DAQ-2204/2205/2206 User's Guide. ADLINK Technology Inc, 2002, (1).
[2] Lv Yongjian, Wang Jin, Xie Wenjun. Application of intelligent interface in aircraft power automatic test system. Measurement and Control Technology, 2002, (9).
[3] Yang Leping, Li Haitao et al. LabVIEW Advanced Programming. Tsinghua University Press. 2003.4