I disagree in principle with the other recommendations made for specific meters. Nothing against the meters or the manufacturers, but there is no simple answer. The answer depends on what you want your bond to do for you.
A 2.5 milliohm bond might be a class R bond, or class A or class L (obsolete MIL-B-5087B terminology). Case by case: Class A/R: You most definitely do not want a meter that puts out 10 Amps and more importantly you want low potential output. And unless you are going to remember to measure the bond in both directions, you want a meter that puts out an ac signal (so that any galvanic potential in the bond is averaged out). The answer, the HP4328A/B or whatever it is now from Agilent. If Agilent isn't making this anymore, I would hunt around for a used one for a class R or class A application. The reason for low current low potential is that is what the class A/R bonds are working against. A 20 V/m field impinging on a shielded cable will induce a maximum of 30 mA and 1.5 Volts coupled to that shield. The bond has to conduct that current to ground such that the potential does not drop across the protected circuitry. There could be a very fine film of non-conducting material between say connector shell and equipment chassis, or between equipment chassis and ground plane and the potential sourced by a brute force meter would punch right through it, whereas a 1.5 Volt signal wouldn't. The brute force meter wouldn't give you a true measure of the bond performance in a class A/R situation. Class A is also looking at milliamp currents and even microvolt potentials Class L: Brute force is exactly what you want. Lightning isn't worried about a thin non-conducting coating - it will punch right through. Of course you may get some interesting induced effects from the punch-through potential, but that is part of the effect. Also the lightning bond has to be able to take lightning currents without damage, so the higher current meter is the way to go for that reason as well. Ken Javor > From: "Amund Westin" <[email protected]> > Date: Fri, 11 Mar 2005 08:15:09 +0100 > To: "EMC-PSTC - Forum" <[email protected]> > Subject: Milliohm meter > > We are going to measure grounding / bonding staps, which shall not exceed > 2.5 milliohm. > Any recommandation for a well good milliohm meter? > > Best regards > Amund Westin, Oslo, NORWAY > > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society > emc-pstc discussion list. Website: http://www.ieee-pses.org/ > > To post a message to the list, send your e-mail to [email protected] > > Instructions: http://listserv.ieee.org/listserv/request/user-guide.html > > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > > Scott Douglas [email protected] > Mike Cantwell [email protected] > > For policy questions, send mail to: > > Richard Nute: [email protected] > Jim Bacher: [email protected] > > All emc-pstc postings are archived and searchable on the web at: > > http://www.ieeecommunities.org/emc-pstc > This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
