Customer Solutions

Helicopter Gear Drive Computer Based Test Bench

Author(s):

Sergey Andreev, ViTech Co. Ltd.

Industry:

Aerospace/Avionics

Product:

Signal Conditioning

The Challenge:

To build the automated T&M system for monitoring and control of helicopter’s gear drive’s test bench previously manually controlled. The parameters consist of temperature, pressure, vibration, frequency, torque, relative frequency phase difference, electrical power and so on, and is included both UUT and test bench control parameters.

The Solution:

PC-based system with DAQ boards, SCXI, and SSR modules controlled by LabWindows/CVI. Graphical capabilities of LabWindows/CVI and Windows became a good base for ease of use interface. Flexibility, compatibility and power of computer based DAQ hardware in conjunction with software consumed at least two times less efforts and time for development and installation.

Abstract
Transmission’s test bench equipped with several types of hardware such as:

• two aircraft engines and launch engine
• three hydraulic brakes
• gear drive
• pumps, valves
• generators and electric drive

LabWindows/CVI from National Instruments was chosen because of the speed and simplicity of developing both operators interface and hardware communication regardless of channel’s quantity and sophistication. The program consists of two main parts: the control of test bench equipment and measurement/report program. The control software consists of manual and automated control programs for the test bench units. Measuring procedures, report generation, automated calibration routines are included in measuring subsystem. The program also is featured setup routine, useful utilities and help subsystem.

We have developed this solution in industrial process control and measurements systems area. The goal was in full test bench automation on machinery plant in St.Petersburg, Russia. The helicopter gear drive test bench represents a big industrial room filled by oil and water pumps and pipes, aviation engines, electrical motors and valves. The measurement system is based on industrial PC (Pentium MMX 200 MHz, 32 Mb RAM), data aqusition boards and signal conditioning modules (SCXI) from National Instruments (refer figure 1).
We used the multifunctional DAQ board AT-MIO-16F-5 from National Instruments for measuring analogue parameters - temperature, pressure, and vibration. Pressure and temperature signals are conditioned by SCXI isolation amplifiers: SCXI-1120, and SCXI-1121. For temperature measurement Pt100 RTD sensors, K-type and L-type thermocouples (with cold junction compensation by SCXI-1320 terminal blocks) are chosen. Common types of pressure sensors are used for air and differential pressure signals.

PC-TIO-10 timing cards are used for precisely measurements of drive’s shaft rotate frequencies. Inductive sensors generate frequency signals, which used for frequency measurement purpose as well as for torque measurements. Those signals are conditioned to TTL levels and transmitted to PC by custom optically isolated amplifiers. The same circuits form relative phase difference signal for two signals to one impulse signal sequence, which is characterized torque applied to gear drive’s shaft. This technique helps us to reach great rejection of industrial noise (from switches, latches and motors). PC-TIO-10 card is used for oil flow measurements and hydraulic brakes control valve position encoding. PC-DIO-96 is used for digital input of latches state and alarms from test bench mechanisms. DIO signals are conditioned by isolated SSR modules.
Program to hardware communication is based on NI-DAQ driver software. LabWindows/CVI from National Instruments provide us with speed-up, flexibility and simplicity of developing graphical user interface for Windows 95/98/NT. Standard ANSI C compiler generates high-speed executables. Our system has many of analogous and digital channels, therefore high speed of execution is very important.
The software consists of several groups of functions, such as:

1. Pseudomanual interactive control of the test bench mechanisms, like engine launch and stop, turn valves on/of etc. This possibility permits user to check and control functionality of partiqular equipment. The system is automatically performing error condition recognition, for example no operation of relay or end switches.
2. Automated control of the test bench. This group implements the operation sequences according test schedule. Engine launch and speed level set up perform automatically. The current values of most important parameters (drive shafts rotate frequencies, compressor pressures, torsion torques) are displayed on user screen (refer figure 2). All others parameters are displayed in the list control with slow and fast scroll bars. The error and explicative messages are displayed in the message list on the bottom pane. During the testing the Measurement Report is automatically filled on personal computer hard disk in real-time.
3. Measurement Report. You can view and print any records from archive. The measurement journal includes both the textual protocol with standard readings on test regimes and historical trends of some (user selected) measurement parameters. User can set any period for data accumulation speed.
4. Automated calibration routine of measurement channels. Flexible sensor selection, error handling and schaling for all channels are achieved by simple and not tiring procedure.
5. The program setup, utility functions of test bench control, help system. In our program we highly attended on user faults protection. For example, all operator actions in working through gear drive test process are written into the special "internal use message protocol". In case of alarms or the breakdown user can analyze record to determine operator fault, test bench mechanisms misoperation or program guilt.

The deep interaction between hardware (DAQ boards from National Instruments) and software (LabWindows/CVI, Windows 95) makes our system handy, easy in use and high-speed in execute. Operatots as novice computer users quickly accepted friendly user interface. Flexibility, compatibility and power of computer based DAQ hardware in conjunction with software consumed at least two times less efforts and time for development and installation.

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