Dear Chris, Sorry for the late response due to my EMC Symposium 04 Eindhoven Netherlands trip. I do not have a direct answer to this problem, but would like to question the whole calibration activity. Is this worth the cost? Is it accreditation 17025 or what is driving the cal effort? I also work as EMC Test Lab assessor under ISO 17025. My background is here is TEM waveguides (EUROTEM, GTEM see homepage-but this does not mean I always have to promoting it!)
Suggestion 1: If at all, get the fields measured with a calibrated E-Field probe in all E field component directions (x,y,z). This will quickly tell you how far this thing is from a reasonably clean TEM waveguide. TEM wave guides should basically only support this wanted energy transportation mode (propagation direction) and no other higher order modes. E, H, P- Vector should be perpendicular and .....sorry , end of lecture... I know from literature (University of Hanover Prof. Garbe, published in German only) and from other sources the fields are anything but TEM in this G-Strip test facility and change way over 20 dB with respect to location and frequency in the empty cell. The potential EUT loading and other negative side effects are not considered here.This is not to say it is useless. Comparing the same type of EUT, under similar conditions, to find "deltas" may work fine. There are some precompliance applications, but be prepared to accept very high measurement uncertainties. Suggestion 2: Details about all kinds of TEM devices (including cal) may be found in the (new) basic standard IEC 61000-4-20 ( www.iec.ch <http://www.iec.ch> ) Just a hint switching to reverberation chambers IEC 61000-4-21 may be worth looking at it, if e.g. you a only interested in the higher emission and immunity frequency range. Here basically a shielded room with high (bad) standing waves (cavity modes) is converted into an EMC Test Facility with useful statistical "free space field conditions -377 Ohms " by changing the boundary conditions with a paddle. Advantages no turntable, very little drive generator power needed to get high fields (typ 30dB less than in absorber chambers), fully automated etc. Disadvantage below ca 200 MHz the room size approaches shielded room size of 3 or 5m (Anechoic) chambers. May be this helps rgds Diethard Best regards Dr. Diethard Hansen EES President, Principal Consultant, Trainer US Senior NARTE certif. EMC Eng. 001937NE EMC+Automotive+Telecom QM+techn. EA-Auditor Euro EMC SERVICE (EES) Dr.-Ing. D. Hansen POB 64, Bahnhofstr.39, CH-8965 Berikon 2, Switzerland, Swiss VAT (Mwst.)No.:323214 tel./fax: +41 566 33 73 81 German mobile phone: +49(0)1736015909 www.euro-emc-service.de <http://www.euro-emc-service.de> [email protected] <mailto:[email protected]> ( mailto:[email protected] <mailto:[email protected]> ) Consulting+Seminars+R&D-Projects Marketing+CE-Testing+ww.Audits From: [email protected] [mailto:[email protected]]On Behalf Of Chris Maxwell Sent: Mittwoch, 8. September 2004 17:31 To: EMC-PSTC Subject: Calibration of Comtest G-Strip Amplifier All, We have a Comtest G-Strip system. The system consists of a 70cm stripline cell, an HP8647A signal generator, A comtest amplifier and a computer used to control the whole system. Over the years, we have sent the signal generator and amplifier out to be calibrated separately; and they have come back with shiny new calibration tags on them. We recently switched calibration services; and the new guys are having problems calibrating the amplifier. They claim that they can't get it to turn on. I know that the amplifier has an interlock connection to the strip cell (BNC input). I assumed that this was looking for a relay closure from the magnetic proximity switch in the stripcell door (the switch enables the amplifier only when the stripcell door is closed.) I told the calibration guys to short this BNC input to defeat the interlock and get the amplifier to run. This didn't work for them. The calibration guys have asked that I bring the whole shebang (stripcell, computer, signal generator, cables...) over to their place for calibration. Before I do that, I lay myself at the mercy of the group...especially if there is someone from COMTEST following the group. The guy who used to calibrate this amplifier did one of two things: either he just put a sticker on it and never ran it; or he knew how to get the amplifier to run by defeating the interlocks and analog inputs. So these are my questions: (Note that system configuration is Comtest G310 stripline cell, Comtest GPA306 amplifier and HP8647A signal generator) 1. Is there a way to get this amplifier (Comtest GPA306) to operate without the rest of the system? i.e. how does one defeat the interlocks without there rest of the equipment present. 2. Would I be better off having the whole system calibrated by measuring the field strength within the chamber? Any and all advice/responses would be appreciated. Thanks, Chris Maxwell ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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