MIL-STD-461F Testing Deviations Save Time and Money

Some Military EMC testing projects are routine.  This post describes a recent one that wasn’t.

Hydraulics International, Inc. asked us to test its four-wheeled 2-ton hydraulic power generator (pictured in MET’s Military EMC chamber), which is used to check the flight control of the Bell Boeing V-22 Osprey.  The V-22 Osprey is well known for its Rolls-Royce engines that tilt, allowing it to take off like a helicopter and fly like an airplane. 

The test plan was based on MIL-STD-461F, but MET was able to get approval on a couple deviations to save the customer time and money. 

The first deviation was to decrease the unit’s RPM during testing.  The test procedure called for measurements taken at 2,500 RPM, but MET was able to justify a lower RPM by proving that the unit’s electronics would not be affected by its engine speed.  This deviation was important because the EUT’s 160 HP diesel engine would heat the military test chamber rapidly when run at high RPM.

The second deviation was for test method RS101, which normally requires many close proximity measurements using a small radiating loop sensor.  For this large EUT, a non-deviated test plan would have required 60 hours’ worth of testing just for RS101.  MET was able to acquire a deviation from the Navy by getting permission to take measurements only near the unit’s electronic control panel.

A challenge that did not require a deviation was how to exhaust the diesel fumes out of the test chamber, while maintaining the 200 V/m EMC chamber’s RF shielding effectiveness.  Radiated emission ambients were shielded by using a small diameter steel exhaust tube that was secured to the chamber ceiling using metal-to-metal bonding techniques.

This project also required Data Item Description (DID) documentation.  Read more about DID documentation, its benefits, and process on the bottom of this Military EMC testing page

Have an upcoming MIL-STD-461 test requirement?  Ask about MET’s complimentary MIL-STD-461 Pre-Testing Program, which greatly increases your chance of first time compliance.  Contact us today.

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