Vibration, noise and strain gauge measurements are required from the system. Test of electronic modules, both externally (transmitted and received signals) and internally (communication on two Arinc 429 buses) create part of the measurement. The system must be open enough to enable later expansion with analog measuring modules to measure signals generated by aircraft and to generate signals received by aircraft. It is assumed that strain gauge measurements, vibration measurements and noise measurements will not be performed simultaneously, but may be performed concurrently with analog signal measurements and bus tracking.
The VXI technology is used. Modules are housed in the Tektronix VX1410 IntelliFrame ™ chassis. The chassis contains 13 module slots. Is powered from 220V network as well as from aircraft internal power. Source and cooling power are sufficient for virtually any VXI module on the market. The chassis (and hence all the modules in it) can operate on board aircraft up to 15,000 feet. A Pentium Pro plug-in module operating at 200MHz is used as a measuring computer. This PC-compatible VXIpc-860 is plugged into the VXI frame and forms with the system compact unit . The computer is equipped with a SCSI port, keyboard and mouse. Depending on the type of test being carried out, the computer is alternatively complemented by either a high-quality 15 “SVGA color monitor or a flat display.
Measuring VXI set
The monitor provides excellent viewing, but requires 220V ~ and is not resistant to environmental influences. It is therefore suitable for laboratory testing. Conversely, the flat panel display is small and durable and, when mounted on a VXI frame, allows for a completely compact system. It is an active color TFT display with VGA resolution. Its power supply is from the VXI frame. The LCD screen is complemented by a Touch Screen, which allows to control measuring programs by touching the program buttons on the screen.
Rewritable optical discs are used for archiving data packages and transferring them to an evaluation system. They are characterized by very fast data writing, comparable to a hard disk.
Measurement of analog signals is realized by a pair of VXI modules, namely 61/2-digit multimeter Tektronix VX4237 with relay module VX4385.
The multimeter measures DC and AC voltages, DC currents and resistance. The sampling rate (at a certain loss of resolution) can be up to 100 samples per second. The VX4385 relay module contains 128 relays in configurable wiring. It can be used as a two-wire 64-channel multiplexer, or as a four-wire 32-channel multiplexer, or, for example, only half can be used to measure analog channels and the rest can be used to increase the number of simultaneous measurement channels. Contact closing time is 10 ms.
The required strain gauge measurements on 32 channels with a sampling frequency of up to 5000 bps are performed by four 8-channel loggers from Analogic, type DBS8700.
Each DBS8700 digitizer contains eight differential inputs, a 16-bit resolution converter and a maximum sampling rate of 200 kSa / s. Each is also equipped with a pair of DMA channels to speed up data transfer to the computer. This type of digitizer is often used for measurement in the aerospace and automotive industries.
Four DBS7800 modules, common for strain gauge measurements, will be used to measure vibration signals on a maximum of 32 channels with the required sampling frequency up to 15 kHz. A signal processor is used for fast data analysis and digital data filtering.
Four DBS8700 modules are again used to measure noise on 4 channels at a sampling rate of up to 100 kSa / s; each module ensures measurement of one channel.
The VX4224 counter / timer up to 200 MHz with 9 digit resolution is used to check the frequency setting.
The Tektronix VX4750 up to 25 MHz generator with FM / AM / PM modulation is suitable for sensitivity and selectivity control.
Arbitrary Waveform Generator with Predefined Functions and Possibility to Define Arbitrary Waveform The Tektronix VX4792A is used as a modulation source for a functional generator and for simulating non-standard signals.
The system performs not only measurements but also pre-evaluation of measured data. For fast signal processing and filtering (especially for monitoring pre-processed data, eg FFT, already during the measurement), a signal processor equipped with an Inmos T800 transputer is added to the system and supplemented with appropriate firmware. This set is part of a 12-channel Tektronix VX4240 single channel digitizer and waveform analyzer with a maximum sampling rate of 10 MSa / s. The digitizer is also used to measure fast variable signals and as a digital oscilloscope.
A memory module that receives data directly from the VXI bus can be used for operative and fast storage of dynamically measured data with aggregate sampling rates of up to 180 kSa / s. It is a Brűel & Kjaer 4703 module. It can be equipped with a memory of up to 128 MB, with 64 MB of memory a capacity of at least six minutes of recording 15 channels of vibration or 32 strain gauge channels is sufficient. The data stored in the module can be written to disk media in blocks.
The VX4428 module, equipped with four independent receivers and four bus transmitters, is suitable for Arinc 429 monitoring. Modules can be connected independently of four different buses, but can also be used to monitor four different events on one bus. They can receive data, either all or set type. Broadcasting is possible on a number of levels and it is also possible to programmatically introduce errors into communication (wrong data, wrong format, altered electrical level, etc.) and monitor the system response.
The system includes a number of programs for measuring and evaluating data. These are eg programs for monitoring certain quantities (eg. monitoring the communication of the FM receiver on the bus and on the analog side). Complex programs for certain measuring cycles, eg in flight, unattended, with data storage on an optical disc and additional evaluation, can also be used. In flight, only the data is pre-evaluated to decide whether it is worthwhile to continue the test.
Main advantages of this system:
- highly reliable,
- the system will become very morally obsolete,
- one system for developmental measurements and for complex aircraft diagnostics,
- gradual purchase of necessary modules, possibility to lend modules for testing or during the eventual repair,
- guarantee the functionality of the system as a whole,
- one partner for solving possible complaints of technology and programs, domestic service,
- the most suitable modules of different manufacturers,
- reserve for further expansion,
- high processing power and high throughput of the system,
- built-in signal processor and memory
- network connection,
- custom-made measuring programs, based on the agreed project, are based on the user’s requirements, so there is no need to adapt their requirements to the finished program; detailed documentation is kept in mind,
- user’s participation in the creation of the program, further modifications of the program are made by the customer operatively, or they can be commissioned,
- direct contact to program authors, hot line.
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