Here's my two cents worth: 1) If I interpret you correctly, a green wire connection from the power grid has not been made to the room. This could conceivably be a safety issue. If you don't believe me, measure resistance between your dedicated chamber ground rod and the facility rod closest to you (I've done this, and even after a good rain I measure open circuit). In my chamber, I connected the power grid safety ground to the room AT THE SAME POINT at which I connected the ground rod. You can say it is a ground loop, but it does not generate power frequency currents flowing on the room surface, which is the only reason I can think of for maintaining an spg. There is absolutely no reason for maintaining a chamber spg for measurements made between 30 - 1000 MHz.
2) If you plan on running magnetic measurements at power frequencies per MIL-STD-461 RE01 or commercial variations thereof, then an spg is mandatory in order not to pollute your ambient. Of course, you also have to watch your instrumentation grounding if the room has another connection to earth ground. You cannot both connect coax at a grounded chamber feedthrough connector and to a grounded spectrum analyzer chassis outside the chamber. ---------- >From: [email protected] >To: [email protected] >Subject: FW: Chamber Grounding >Date: Wed, Nov 3, 1999, 6:25 AM > > > >> Our chamber is grounded/isolated per the instructions of the vendor. We >> have one copper clad ground rod installed through a hole drilled in the >> slab adjacent to the corner of the semi-anechoic chamber. Other grounds >> are isolated from the chamber (conduits, air pipes, water pipes, service >> entrance safety ground, etc.). The ground comes from the ground rod, not >> the service entrance. >> >> 1) Is "single-point-ground" as described above for Tempest? Is the >> degree of isolation useful for typical commercial work? The chamber spec >> is 100 dB isolation. For our immediate work, 60 dB of isolation is >> adequate. Is there any correlation between chamber isolation and >> effectiveness of the ferrites for the uniform field required for immunity >> testing? Is there some other observable sensitivity such as degraded RF >> measurements that would result from not observing the isolation? What >> would the manifestations be? >> >> 2) Using the isolation as described above, has anyone experience ground >> loop problems between the service entrance power and the local chamber >> power distribution due to the "single point ground" concept defined above? >> >> >> >> Don Umbdenstock >> Sensormatic >> > > --------- > This message is coming from the emc-pstc discussion list. > To cancel your subscription, send mail to [email protected] > with the single line: "unsubscribe emc-pstc" (without the > quotes). For help, send mail to [email protected], > [email protected], [email protected], or > [email protected] (the list administrators). > > --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
