Aircraft electronics and other electrically-powered equipment must be tested under extreme power conditions to ensure it will operate reliably once in the air. In the military world, MIL-STD-704 (now up to rev. F), ‘Aircraft Electric Power Characteristics’, establishes the requirements and characteristics of aircraft electric power.
The standard is not only used by the US military and military contractors, but has also been adopted, either directly or indirectly, worldwide. For example, the Chinese standard, GJB 181, ‘Characteristics of aircraft electrical power supplies and requirements for utilization equipment,’ is largely based on MIL-STD-704.
MIL-STD-704 actually defines the power characteristics of an aircraft electric power system, not the test requirements. For guidance on testing, there is a series of eight handbooks that specifies tests for different types of input power, titled MIL-HDBK-704. These guidance documents, including MIL-STD-704 (revisions A through F) are available online at EverySpec.Com.
The tests specified in the MIL-HDBKs is designed to ensure that airborne utilization equipment, which is defined as equipment that receives power from the aircraft's electric power system, is compatible with the power system. To run these tests, a sophisticated power source is essential to simulate various power conditions. In addition, you also need whatever equipment is required to monitor the unit under test (UUT) while running the test.
AMETEK Programmable Power has provided test equipment for compliance tests for airborne utilization equipment for decades. Its test equipment systems cover the latest versions of MIL-STD-704 to make it more effective and easier to use. Its MIL-STD-704 test solutions are in use by customers in the USA and all over the world.
MIL-HDBK-704-1 through MIL-HDBK-704-8 specify the acronyms used for the seven power groups. These are:
As an example, let's look at the tests specified by MIL-HDBK-704-3. This document provides guidance for testing utilization equipment that requires three-phase, 400Hz, 115 V AC power. It specifies 18 different test methods:
For every test method, MIL-HDBK-704-3 defines a detailed test procedure. Test Method TAC 109, ‘Normal Voltage Transients’, for example, specifies:
The AMETEK Programmable Power MIL-STD-704 test software supports this test method, as well as other MIL-HDBK test methods. There is no need for additional programming. The complete test process can be accomplished by clicking on the tests you wish to perform.
For more information on avionics power testing, read the full article, “A guide to avionics power testing” on Aerospace Testing International’s website or contact AMETEK Programmable Power toll free at 800-733-5427 or 858-450-0085 or email sales.ppd@ametek.com.