Noise problems overcome at MBDA

Following MBDA's completion of its £multi-million, state-of-the-art, environmental test and systems engineering lab it called on Vibratech to fine tune elements of the seven independent vibration test systems.

The development at MBDA's Stevenage site, one of the largest facilities of its kind in the UK, provides clients with unprecedented environmental test and systems engineering facilities. Vibratech, based in Royston, Hertfordshire, primary contract from MBDA was to design, manufacture and install systems capable of remotely controlling and monitoring the seven independent vibration test beds.

This resulted in the control room being installed with six identical control cabinets containing an LMS vibration controller, signal monitoring equipment and emergency vibration stop function. Additionally a centralized master patch panel provides the flexibility to allow a selected control position to be used for a specific vibration system.

Each of the shakers was fitted with a 16 channel microdot connector box to allow accelerometer connection from the unit under test This microdot box is connected to an identical box fitted on the test cell wall thus reducing the need to trail accelerometer cables to charge amplifiers that need to be situated away from the shaker and test item.

Also installed is a wall mounted Accelerometer box, this multi function unit contains the 16 BNC channels for the charge amplifier normalized signal to be routed to the Master Patch panel.

The drive signal between the control room master patch panel and the system Power Amplifier is also routed via the wall-mounted accelerometer box. Power Amplifier drive from a local connection, Amp Status and Emergency Stop functions are all provided through multi pin connectors routed to the Power Amplifier.

One of the biggest challenges facing Vibratech was that of ambient noise levels. Due to the lengths of cables that were in excess of 50 metres and the locality of large plant equipment, the noise levels were unacceptable. Vibratech implemented several measures to bring these levels within the acceptable 50 x 10 -3 g rating specified by MBDA.

These methods were, to use low loss twin screen cables giving careful thought to the specific routing of these cables. The elimination of earth loops was of great importance and by earthing cable screens and comprehensive grounding within the Control Cabinets these were eliminated from the signal line. In addition each Control Cabinet contains 16 channels of active filtering providing increased levels of noise reduction.

Marc Brown, MBDA's Group Head of Environmental Engineering Test complimented Vibratech on its achievements saying: "Throughout the process we felt very comfortable with everything Vibratech was proposing. The new system of control panels and master patch panel has simplified a process that was overly complicated."