re you considering the purchase of an EMC chamber for in-house testing? If so, what factors should you consider for determining if the investment is a wise choice or if the continued utilization of a third-party test facility is the better option? For some, the decision is easy. The volume of products they intend to develop that require EMC testing is so low that the cost to bring EMC testing in-house is clearly not justified. For others, they may have a lot of new products in development (or plan to) and taking them to an outside EMC testing facility on a regular basis is not only costly, it is inconvenient and time-consuming. For those in this latter group, trying to decide if they should bring EMC testing in-house is not always a straight-forward decision.
- Number of expected test events over the next x number of years (x might be three, four, or five, for example).
- Cost of item 1 above if conducted out-of-house at a third-party test facility (include travel cost and time, lodging, meals, flights, in addition to test fees for each expected test event).
- Cost of the EMC chamber and all associated equipment (antennas, turntable, amplifiers, spectrum analyzers, cables, filters, line impedance stabilization networks, etc.).
- Cost to install the chamber.
- Cost of calibration and chamber verification tests over the next x numbers of years.
- Cost of in-house labor and staff to run and maintain the EMC chamber and all associated equipment over the next x number of years.
- Cost for electricity to run and light the chamber over the next x number of years.
- Cost to train in-house staff to run the chamber.
- Cost for accreditation of the tests to be performed in the chamber and laboratory management.
- Depreciation of the chamber over x number of years.
- Cost of any other item you can think of.
- With an in-house chamber, you can customize the configuration of filtering, power, turn-table size, size of the chamber, cooling, heating, size of the doorway, lighting, EUT monitoring, size of antennas, etc. to accommodate the unique requirements that only your EUT has. When using a third-party facility, you must utilize whatever configuration they have available, which may or may not require extra effort on your part to “make it work” for your unique EUT setup.
- Your in-house chamber is available for testing any time you need it (24/7).
- If your EUT fails testing and you need to go into troubleshooting mode, you don’t have to worry too much about the clock ticking and over-time, getting removed from the chamber, and wasting expensive third-party lab test fees.
- You will never again go back to your organization with a non-compliant product, after having spent a lot of time and money testing it at a third-party test facility trying to obtain passing results.
- Engineering expertise (those who know the product and the design), are on-site, nearby, and available to help troubleshoot the EUT as required.
- Your facility has more options for fixes (capacitors, ferrites, resistors, etc.) should they be required.
- There are technicians on staff who are well-trained in making modifications on the fly should modifications to pass be required.
- Determining if a minor modification to the product or if a part replacement for an end-of-life component causes a non-compliance is much quicker and easier.
- The time required to get the product to market is much quicker.
- Maintaining continued compliance is easier. You can re-test your device anytime you suspect a change might have been implemented that may affect compliance.
- Customer-witnessed tests can be scheduled anytime it is convenient for you and your customer.
- Selection of a chamber is determined by the standard being tested to. Some types of EMC Chambers are: Commercial, MIL STD/DO-160, CISPR 25 and Reverb.
- Commercial chambers are used for IEC and CISPR standards for Emissions and Immunity testing. Typically, “Semi – Anechoic” and achieve CISPR16 (Emissions) and IEC 61000-4-3 (Immunity) chamber performance requirements.
- Semi-Anechoic Chambers are strategically lined with absorber and ferrite to meet specifications without fully lining all surfaces.
- Verification for CISPR 16 compliance is Normalized Site Attenuation (NSA) (26 MHz-1 GHz) and Site Voltage Standing Wave Ratio (sVSWR) (1‑40 GHz). This verifies the chamber “Quiet Zone”. Quiet zones are normally equal to the turntable diameter. EUT’s can’t be larger than the quiet zone.
- For compliance, variations in the quiet zone performance cannot exceed +/-4db for NSA and 6dB for sVSWR.
- Verification for IEC 61000-4-3 is a field uniformity test. Typically, a 1.5m x 1.5m vertical plane consisting of 16 points spaced 0.5 m apart is the measured area. At least 12 Points must vary by >6dB.
- MIL STD and DO-160 chambers can be Semi-Anechoic or Fully Anechoic. Standards require the absorber have a minimum absorption of 6dB from 80MHz to 250MHz and 10dB above 250Mhz. A table with a conductive top is used for testing the EUT and is bonded the shield ground.
- CISPR 25 chambers are fully lined on walls and ceiling, contain a similar table with metal lining on top, and must pass the Long Wire Test or the Reference Site Method test to meet the Standard.
- Reverb chambers rely upon the reflectivity of the walls and an internal movable paddle to reflect generated signals and increase the value of V/m generated from the transmit antenna.
- Information needed to design a reverb chamber is the lowest frequency, the test volume, maximum V/m, and standard to be tested to (MIL STD, DO, ISO).