Hi, I still disagree with the general use of filter connectors in an EMC test set-up at the egress.
If you look at MIL-STD-461C and the test methods document MIL-STD-462 (which is what he is testing to - RE-02), you will see that you are required to test in a simulation of the "actual installation and usage". This is located in MIL-STD-462 section 4.2.2.3 where it says that "Interconnect cable assemblies and supporting structures shall simulate actual installation and usage." MIL-STD-462 section 4.2.2.5 on Loads also requires you to use loads that are "equivalent for which it is designed". It further states that "The loads used shall simulate the resistance, inductance, and capacitance of the load". Filter connectors at the chamber egress would be additional capacitance and possibly inductance (type dependent) that modifies the simulated "load" that is supposed to look like the application. Now, if the application or user equipment has filters or filter connectors at their egress, you would be simulating the proper "load" and be compliant to MIL-STD-462. You are also required to meet a minimum of 6 dB margin below the limit line with your EUT "deenergized" unless you have to test under section 4.2.8 (Emission Measurements in the Presence of High Ambient Fields). The filter connectors will help you meet the required ambient margin, but should not be used as a general rule. You are correct about filtering power (AC and DC). It is usually expected to have 100 dB isolation from 10 KHz to 1 GHz. Power is different in that you are required to have capacitors (or LISNs for 461D/E) for RE-02. During testing, we intentionally measure emissions from the EUT during Conducted Emission tests and isolate emissions to the EUT not power cabling from the chamber to the capacitors (or LISNs for 461D/E). The capacitors/LISNs are to normalize the impedance for obtaining repeatable test data. This is different from signal line filtering where the intended signals may be modified (edge rates limited) causing errors in measured data from the lab versus the customer application. If you use filter connectors at the chamber egress in your lab, the cables appear to have the same RF impedance. This is very likely *not* the same as the intended application. Since all test labs do not use filter connectors at the egress, there may be wide measurement variation between labs. This would be the case from lab data with filter connectors to the customer application of the product. What this all means is that you need clean exercise equipment, cabling, and well bonded cable shielding to meet EMC test set-up requirements. It also means that you need a clean Electromagnetic environment like an ante room for the exercise equipment. You may also need a room for the measurement equipment to shield it and the antenna cabling from the ambient Electromagnetic environment. The best way to control these set-up problems is to use a chamber with an Ante room for the exercise equipment. This is a shielded enclosure (room) that has an egress panel between the EMC test chamber and the ante room. The door may be closed to prevent outside emissions from being conducted onto exercise cables and re-radiated on cables in the EMC test chamber. At our facility, we have a 40' X 40' X 28' shielded chamber with Anechoic material and ferrite tiles, 12' X 16' Ante room chamber, and 10' X 12' measurement equipment room, plus a 12' X 16' development chamber. We have never used filter connectors through the chamber egress, we don't think it is proper set-up. But, others may not have the facility to do this. While every situation may not be able to be tested this way, in my opinion, using filter connectors as a general rule for a MIL-STD-461 EMI test set-up should be discouraged. Meeting MIL-STD-461 levels is difficult, but can be done with careful attention to lower level source suppression design attributes, Signal Integrity design, well thought out containment methods, and well designed/built cabling. These are always less expensive and less painful at the beginning of the design cycle rather than at the end. One last thing is that if a military customer agreed that filter connectors are acceptable for the test configuration, they have full authority to accept the test configuration. In that case, I would expect to have this well documented in my proposals, EMC Test Plan, and EMC Test Report. Sorry for the long response. Philip Ross Wellington Mgr. Signal Integrity & EMI L-3 Communications CSW From: Cortland Richmond [mailto:72146....@compuserve.com] Sent: Wednesday, February 19, 2003 7:33 PM To: ieee pstc list Subject: RE: RE02 cabling problem Philip Ross Wellington wrote: >> I do not recommend that you use heavy filtering at the chamber egress wall to control emissions for a couple of reasons... << Valid statements. However, it's necessary to control chamber ingress, otherwise the test would be contaminated by the outside EM environment and no good test could be done. An external signal filter does that. We heavily filter POWER, after all, and for the same reasons. Cortland This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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