Electrical safety testing (EST) is often performed by manufacturers of electronic products to ensure the safety of their customers and learn more about their products. Properly performed, basic EST functions such as AC high-potential (hipot) testing, DC hipot testing, and insulation resistance (IR) measurements can help to identify and eliminate manufacturing problems before they become too widespread in production or even become part of shipped products. Performing EST as part of manufacturing production can provide a great deal of insight into the design of an electronic product and often lead to ideas on improving the reliability of that product.
In general, EST measurements are performed during two different stages of a product lifetime: during product research and development (R&D) and during the manufacturing process. R&D testing is typically a learning process and as a way to avoid potential safety issues with a product. EST production line testing is usually performed on all of the products from a manufacturing facility, to ensure consumer safety.
The tests themselves involve applying different forms of electrical stress as a means of detecting problems, since the safety of an electronic product can be compromised by faulty insulation or a poor ground. Electronic industry standards for construction quality and electronic safety and safety standards are established by regulatory agencies such as Underwriter’s Laboratories (UL) in the United States. While not legally required, achieving a safety agency listing such as from UL is essential for electronic products selling into competitive markets.
What Kind of EST Measurements?
For example, the dielectric voltage-withstanding test, which is more commonly known as a hipot test, provides a way to stress the electrical insulation far beyond the levels that it would experience during normal operation. The test, which can be performed with either AC or DC voltage, applies a very high voltage in search of breakdowns in a product’s electrical insulation. Some amount of leakage current will flow due to the high applied voltage, and a hipot tester can typically detect the leakage current according to a tuned or programmed leakage current threshold limit, which is often according to a value specified by an electrical safety agency’s standards.
An insulation resistance (IR) test is another way of evaluating the quality of a product’s electrical insulation, by applying a DC voltage to the insulation and measuring the leakage current resulting from the applied voltage. High voltages are used to produce the electrical stress levels for these different tests, usually several thousands of either AC or DC volts. The amount of time that the test voltage is applied will vary according to the nature of a test, with production tests lasting routinely for much shorter durations than for EST measurements performed as part of extended design testing being used to study the overall electrical integrity of a design.
Instruments capable of both AC and DC hipot tests are available from a number of test equipment manufacturers, with some clear differences between the two forms of hipot tests. For example, an AC hipot test alternately stresses the insulation under test in both polarities of the applied AC energy, for efficient testing, although DC hipot testing can be performed at a much lower current level than AC hipot testing. Additionally the leakage current measured with a DC hipot test is a more accurate value of the actual leakage current than for an AC hipot measurement. In general, for all EST instruments, the safety of those performing the testing is a primary concern, and instruments are typically equipped with such features as ground fault interruption and a floating output according to industry standards such as EN50191 to ensure operator safety.
Evaluating Some EST Instruments
What kinds of measurement capabilities are available from some of the latest commercial EST instruments? As an example of a versatile tester, the QuadTech Guardian 500VA Plus performs AC hipot testing to levels of 5 kV and 100 mA and DC hipot testing to 6 kV and 20 mA. It has a 500-VA output rating and programmable AC hipot frequencies from 50 to 600 Hz. The Guardian 500VA Plus has RS-232 and USB ports for remote control with an external computer, and is available with an optional GPIB port for use in ATE systems. The handy instrument is designed for operator safety per EN50191 and it can also operate as an insulation resistance tester among other measurement functions. This is a robust unit at about 54 lbs. in weight, with high-resolution front-panel LCD screen and output connection for an oscilloscope.
The Chroma 19032 Electrical Safety Analyzer is another robust EST measurement tool, packing five instruments in one box, including AC hipot, DC hipot, ground-bond (GB) testing, and IR test capabilities. The analyzer delivers a full 500-VA output for hipot testing of the most demanding electronic products, including motors and EMI filters. It also provides a handy, patented open-short check (OSC) to guard against unconnected cables or bad connections during production testing, helping to minimize damage to products while they are being testing on the production line.
Chroma’s 19036 Wound Component EST Analyzer is perhaps an even more versatile tester, designed for wound wire testing and with high voltage outputs to 5 kV for AC testing and to 6 kV for DC testing, in addition to DC resistance measurements and insulation resistance measurements. It also provides as many as 10 channels for performing multichannel scanning tests. As with Chroma’s 19032, it can be controlled via an external computer, using a USB or RS-232 connection or even a local-area-network (LAN) rear-panel connection.
The Associated Research OMNIA II 8257 EST packs an enormous amount of electrical safety measurement power into a standard rack-mount enclosure, including AC and DC hipot, IR, GB, ground continuity, and line leakage testing. It features a 500-VA rating. Results are shown on a clear, multiple-color front-panel display screen, and users can choose from a variety of automated test ports, including USB, RS-232, Ethernet, and GPIB connections for ATE setups. This tester is even available with a control menu in different languages, to accommodate EST instrument users around the world. Associated Research 7850 tester is an easy-to-use dielectric analyzer in a compact benchtop enclosure. Its front-panel touchscreen simplifies AC hipot, DC hipot, IR, and ground continuity testing, and it can be equipped with any of the standard computer interfaces for ATE applications.
These testers represent a small sample of the many instruments for electrical safety testing applications available on the Axiom Test Equipment website. Explore the wide range of benchtop and more compact testers available for rent or sale by visiting the Axiom’s website at www.axiomtest.com or contact Axiom Test Equipment’s sales department at firstname.lastname@example.org or by calling 760-806-6600.