Designing equipment to be operated onboard Navy vessels is not like designing a consumer product that plugs into a three-prong wall socket. That being said, it’s important to know the characteristics of the on-board power source and test to make sure that equipment can reliably use that power.
Testing AC power sources, such as uninterruptible power supplies, can be a real challenge. These products are often tested with resistive load banks, but this approach does not simulate real-world conditions such as switching DC/AC converters found in many AC powered products.
When performing functional tests, keeping test times as short as possible is often a critical requirement. Time is money, after all. One way to reduce test times is to reduce the latency in setting up signal switch paths, stimulus devices, and measurements. These can all have a significant impact on the overall time it takes to complete a full functional test of a particular DUT.
Calibration is not an option. While today's instruments are more accurate and drift less than previous generations, you still need to periodically check and calibrate your equipment. The way you do this, however, is changing.
In the past, manufacturers would recommend calibration intervals. A digital multimeter manufacturer might, for example, recommend that you calibrate the instrument once a year. When that year was up, you sent the DMM to your company's cal lab or to a third party.
That paradigm is changing. The current trend in metrology is not to blindly follow a manufacturer’s stated calibration interval, but to determine your own interval based on how much each instrument drifts over time and how much risk you're willing to take.
When you purchase a power supply, you need to take into account more than just the price of the supply. The price is just one of the factors in the total cost of ownership. Other factors include:
The success of a product often depends on how well it can handle power transients. To make this testing easier, AMETEK Programmable Power's Asterion makes it easy for users to create custom waveforms that include transients. The output waveforms can include any or all of the following transients:
Topics: AC Power Sources
Power systems operate at frequencies of 50 or 60Hz, but some devices, including personal computers, printers, and some industrial equipment, present a non-linear load and create currents and voltages with frequencies at harmonic frequencies. These harmonics get fed back into the power system and can cause other devices connected to the power source to malfunction. There are several standards that specify the level of harmonics that a particular device can produce.
As noted in an earlier blog post, the tests you run to ensure that airborne utilization equipment is compatible with an aircraft's power system are specified in a series of MIL-HDBKs, specifically MIL-HDBK-704-1 through MIL-HDBK-704-8. 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.
Topics: AC Power Sources
As the number of photovoltaic power-generation systems continue to increase, the requirements for photovoltaic inverters are evolving as well. Conventional electrical characteristics such as over-voltage, over-frequency, anti- islanding intended to verify the inverter’s ability to tolerate power grid fluctuation are changing to meet varying requirements of the modern grid. In addition, the introduction of new requirements for low voltage ride through, high voltage crossing, and reactive power injection mean the inverter must be able to provide appropriate compensation when these grid conditions occur.
To ensure that aircraft electronics and other electrically-powered equipment will operate reliably once in the air, 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. This standard is not only used by the U.S. 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.