To ensure that aircraft electronics and other electrically-powered equipment will operate reliably, you must test them under extreme power conditions. 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. It deals strictly with power quality, and does not say anything about electromagnetic interference.

Even though we call the tests performed to ensure that equipment will perform properly on board an aircraft “MIL-STD-704 tests,” the standard does not describe any tests. For guidance on testing, there is a series of handbooks that describe tests for different types of input power. These include:

• MIL-HDBK-704-1, Guidance for Test Procedures for Demonstration of Utilization Equipment Compliance to Aircraft Electrical Power Characteristics
• MIL-HDBK-704-2, Guidance for Test Procedures for Demonstration of Utilization Equipment Compliance to Aircraft Electrical Power Characteristics, Single Phase, 400 Hz, 115 Volt
• MIL-HDBK-704-3, Guidance for Test Procedures for Demonstration of Utilization Equipment Compliance to Aircraft Electrical Power Characteristics, Three Phase, 400 Hz, 115 Volt
• MIL-HDBK-704-4, Guidance for Test Procedures for Demonstration of Utilization Equipment Compliance to Aircraft Electrical Power Characteristics, Single Phase, Variable Frequency, 115 Volt
• MIL-HDBK-704-5, Guidance for Test Procedures for Demonstration of Utilization Equipment Compliance to Aircraft Electrical Power Characteristics, Three Phase, Variable Frequency, 115 Volt
• MIL-HDBK-704-6, Guidance for Test Procedures for Demonstration of Utilization Equipment Compliance to Aircraft Electrical Power Characteristics, Single Phase, 60 Hz, 115 Volt
• MIL-HDBK-704-7, Guidance for Test Procedures for Demonstration of Utilization Equipment Compliance to Aircraft Electrical Power Characteristics, 270 VDC
• MIL-HDBK-704-8, Guidance for Test Procedures for Demonstration of Utilization Equipment Compliance to Aircraft Electrical Power Characteristics, 28 VDC

These documents, including MIL-STD-704 tests (revisions A through F) are available online at EverySpec.Com.

The MIL-HDBKs describe up to 20 different tests. For example, MIL-HDBK-704-2 includes tests for load measurement, steady state operation at voltage and frequency limits, voltage modulation and distortion, DC voltage component, voltage and frequency transients (both normal and abnormal), and more.

Let's look at one of the test methods. Method SAC109 is the normal voltage transients test. During this test, equipment is subjected to a variety of voltage transients as shown in Table 1.

After you apply the transient, and the power returns to normal steady-state limits, you must conduct a performance test of the unit under tests to ensure that it still meets specifications. For most of the transients, you have to repeat this test five times.

To simplify MIL-STD-704 testing, you need an AC power source that can supply the desired waveforms without having to rig up a lot of external equipment. The California Instruments CSW Series is perfect for this application. The CSW Series has waveform generation features and can be ordered with the software or firmware needed to support MIL-STD-704 tests.