It pays to do preliminary studies before sending products off to the test lab for electromagnetic compatibility problems.
An engineer in a relatively small company usually must rely on experience and tribal knowledge to design a product that is electromagnetically compatible (EMC) with other equipment. Many designers and manufacturers don’t have the luxury of their own in-house RF test lab with an EMI-proof chamber equipped with expensive RF test-gear. That is why it is estimated that more than 50% of products fail the first time through an approved EMC testing facility. And failing is expensive. Retest costs are high and a retest may push back project schedules and market introduction dates.
However, pre-compliance testing has now become much more affordable. Such “early sniffing” can provide a good idea of problems before the fix gets expensive. Standards vary by country, but common EMC regulations for the U.S. are described in FCC Part 15, with subsections depending on whether or not the product is a consumer item. For Europe’s CE mark, EN55011 is the common standard, while some products have even stricter requirements.
Do-it-yourself, homegrown bench testing is becoming more necessary to head off problems passing the required emissions standards. It’s expensive to book an approved, certified test facility to ensure your new product meets EMI emissions limits. But it’s even more costly if your product fails and must go back to the bench to fix radiation issues, then return for a retest.
Fortunately, it is now quite inexpensive to purchase an RF spectrum analyzer with associated near-field probes or antennas, so you can get a first look at basic EMC/EMI problems before they do too much damage. Spectrum analyzers are now affordable—prices of quite sophisticated bench-top units have dropped dramatically in the last few years. They are even available in the form of a USB thumb drive, which can be connected to a Windows PC or tablet.
A set of sniffer probes—which look a bit like bubble wands for kids—can quickly find both the sources of problem radiation and help gauge the success of proposed fixes. The probes can disturb the field being measured, bringing added capacitance in proximity to an unwanted oscillator. Experience will reveal how useful and valuable this EMI tool can be.
Other useful tools for in-house testing include TEM (Transverse Electro-Magnetic) cells for radiated emission and immunity testing, and line impedance stabilization networks for conducted-emission testing of dc-powered equipment. Economical wideband amplifiers can boost the sensitivity of commercial spectrum analyzers or digital oscilloscopes using the scope’s FFT spectrum analyzer setting—but oscilloscopes are often not sensitive enough to provide much useful information.
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