Monday 25 June 2012

Guarding the Hovercrafts' drivetrains!

Monitran is supplying Southampton-based Griffon Hoverwork with condition monitoring systems for 12 of its Griffon 8000TD hovercrafts, ordered by the Indian Coast Guard.

The system, designed and developed by Monitran as a turnkey solution, employs 14 MTN/1100W general purpose constant-current analysis sensors with AC outputs, sealed to IP68 (submersible) and supplied with marine-approved cables. These feed into a bulkhead-mounted waterproof cabinet that contains 14 MTN/8066 g-mac signal conditioning units.

Each g-mac unit provides analogue (AC) outputs proportional to velocity and peak g, which feed into a PCB-mounted microcontroller programmed by Monitran to drive a touch-screen display on the front of the cabinet. Several screen views are available but the most useful show:
The current numeric mm/s values of all sensors;
The mm/s values of all sensors shown as a bar chart, with each bar showing current value, threshold and maximum value recorded; and
The mm/s values of all sensors as lines on a 360o dial.

All of the above also include a colour-coded status indicator; green to denote below-threshold and red to denote above-threshold.

The cabinet also feeds a status indicator in the hovercraft’s cockpit to give the pilot an indication of vibration levels.

Tony Roxburgh, Project Manager of Griffon Hoverwork comments: “A hovercraft’s drivetrain experiences a wide range of loads, in terms of torque and RPM, during operation as it tends to be worked hard when a crew is responding to an emergency. The Indian Coast Guard requested that their 8000TDs be fitted with an integrated engine and gearbox vibration monitoring system to warn the pilot if the drivetrain experiences any abnormal vibrations.”

Other requirements included that the system be lightweight, compact, compliant with marine regulations and itself tolerant to high levels of vibration. In addition, provision had to be made for maintenance engineers to view the vibration levels on any given sensor in order to identify which component(s) might be wearing or developing faults; a requirement that was easily met thanks to each g-mac having a buffered native accelerometer output presented on a BNC connector.

Andy Anthony, Monitran’s Managing Director, comments: “Monitran is increasingly undertaking turnkey projects, and developing engineered solutions from the sensor up. The project with Griffon Hoverwork also exemplifies what can be achieved with a relatively humble, general purpose accelerometer like the MTN/1100W.”

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