RVDT Portable Test Instrument

Collins Aerospace is anew unit of Raytheon Technologies Corporation, formed by the merger of UTC Aerospace Systems and Rockwell Collins in 2018. Collins Aerospace is one of the world’s largest suppliers of aerospace and defence products and have over 300 sites globally. CCS have been involved in multiple projects with their nearby UK Enterprise and Actuation Systems sites, and now internationally, with their Singapore section via Cranfield University. 

A Rotary Variable Differential Transformer (RVDT) Test box for PAT and fault-finding purposes.

Hardware Design

  • Controller and chassis: cRIO 9040 RT Controller and FPGA backplane.
  • Display: 5 in. touch screen Win CE LCD monitor with 680*400 screen resolution.
  • Analogue Input: 4 analogue inputs 16bit, independent ADC, Voltage Range Accuracy ±10V, and simultaneous sampling.
  • Analogue Output: 4 analogue output 16bit, Voltage Range Accuracy ±10V, Output amplifier with low pass filter Signal is 3012Hz (332ms), and frequency precision can be up to 0.003%

Field programmable gate array (FPGA)

FPGAs are semiconductor devices that are based around an array of configurable logic blocks and a hierarchy of reconfigurable interconnects. The logic blocks can be configured to perform as simple logic gates or to perform complex combinational functions. The first commercially viable FPGA was invented in 1985 and since then there has been a huge increase in market competition and applications, with significant improvements in prices and performance dynamics as of 2017 broadening the range of viable applications. Some notable applications have been for hardware acceleration of the Bing search algorithm, acceleration of artificial neural networks for machine learning, and even as full systems on chips (SoC).

CCS use an add-on for NI’s LabVIEW called LabVIEW FPGA to design complex systems efficiently and effectively, this includes an integrated development environment, various IP libraries and debugging features. Here we are using the FPGA to quickly calculate the required variables without the need to upload the test data before calculating so there it is instantaneously shown on the test rig.

      Software Design

        • Initial Start-Up & Graph Screen is the first screen on start-up, once the system has booted up it will begin plotting RVDT and Encoder positions onto the graph.
        • DPMS Screen displays the positions of the RVDTs in volts, the encoder position in revolutions, and the coil Vrms (root squared mean of voltage) from secondary coil measurements. Here you can also zero the position of the encoder with the “Reset Encoder” button.
        • Settings Screen enables the operator to modify the system parameters:
          • Volts the excitation voltage supplied to the RVDT (in Vrms)
          • Oscillatory Frequency the oscillation frequency supplied to the RVDT (in Hz)
          • Pulses per Revolutions the number of pulses per revolution of the encoder

        With options to “Save”, “Revert”, and “Demo”. To save new parameters, revert to the default values, and input random numbers into the DPMs to prove they are responding correctly.

        • About Screen displaying operating system details and contact information for CCS.


        The outcome is a RVDT Test Box housed in a 19” rack inclusive of the 2 and 4 metre harnesses, breakout box and encoder. This RVDT box is not strictly a one-off piece of equipment and multiples could be sold, either to multiple companies or within a company, as an adaptable PAT and fault-finding instrument.


        Similar Projects

        • Aerospace Projects including other test rigs, data acquisition systems and control interfaces, for various aerospace components.
        • RVDT projects for other aerospace companies such as Comar and Goodrich.
        • More applications of FPGAs are being looked into by CCS for a variety of other projects, including other fault-detection rigs and onsite data analysis.
        • International Clients are an increasingly large part of CCS’s client base, with an multinational reputation and on-site visits key to our work.


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