RE: question on measuring bonding impedanceMike, A weld occurs when there is melting of metal. The metal will only melt if it gets enough heat. It will only get enough heat if there is enough of a resistance there (P=IR), or an arc (where the arc-welder gets its name), either of which would mean poor bonding, a failure of the test. A good bond won't be warm to the touch (wait until the current is off before testing my theory) BTW, the connection tested in 1010, 60950 and many other safety standards is the path to ground, which, in a fault, may have to withstand xx amps until the fuse blows or the circuit breaker trips.
Even though my experience comes from my past few employers, my opinions are my own. --- Sam Davis Regulatory Engineer Professional Testing Inc. (512)244-3371 x112 www.ptitest.com -----Original Message----- From: [email protected] [mailto:[email protected]]On Behalf Of Michael Taylor Sent: Monday, April 15, 2002 2:02 PM To: 'Ken Javor'; Robert Wilson; [email protected]; [email protected] Subject: RE: question on measuring bonding impedance I promised myself I was not going to drag out my soap box and jump into this but . . .! (this discussion is limited to only the issue of the measurement of bond impedance - not if the connection can stand xx amps) While MIL 5087 establishes some bonding requirements & methods, for domestic product safety EN-61010 Sect 6.5.1 requires 25Amps (DC or ACrms) or 2x the fuse rating. I have never liked this method of testing. Does it make any sense to test the impedance of a connection by welding it ??? Any of the low voltage (low current) ac bridge or Kelvin methods will tell you the actual impedance of the joint. Or, it will tell you that an oxide layer exists in the bond at that test potential (stress) level. The oxide layer may only be angstroms thick and require a few nanovolts potential difference to punch through, but you know what it really is. Not, what the welded connection has become. The impedance and the area of the bond determine the current carrying capacity. If "proper" testing indicates an oxide layer problem then it can be dealt with mechanical means to establish a "gas tight" connection or with the introduction of a conductive compound. Bell Labs developed the best conductive compound I have ever come across, called NO-OX. Developed to produce a 20 year stable ultra-low Z connection on the DC battery buss bars in telephone switching centers It's exact composition is unknown but I think it includes reconstituted catfish pond sludge (or some equally fowl compound). I remain a firm proponent of finesse not "nuke um & see what's left" although the 1010 standard forces me to do the high amperage test. I do it but I don't like it. I'll put my soapbox away now, it's time for the people in white coats to return me to the home. Regards, Michael Taylor (thawing out in Colorado) -----Original Message----- From: Ken Javor [mailto:[email protected]] Sent: Monday, April 15, 2002 11:44 AM To: Robert Wilson; [email protected]; [email protected] Subject: Re: question on measuring bonding impedance I wasn't going to respond to this one because I know of no standard, and I don't know what you mean by AC, power frequency or rf. But HP/Agilent makes/used to make a bond meter with a 1 kHz signal. The purpose was partly to offset the effects of galvanic potentials: an ac measurement cancles the dc galvanic potential out. ---------- >From: "Robert Wilson" <[email protected]> >To: <[email protected]>, <[email protected]> >Subject: RE: question on measuring bonding impedance >Date: Mon, Apr 15, 2002, 10:46 AM > > > How about the usual method of determining the value of very low > resistances and impedances? Pass a known (relatively high) AC current > through the connection, measure the voltage drop and use Ohm's law to > calculate the resistance (and this is, after all, an essentially > resistive connection). > > Bob Wilson > TIR Systems Ltd. > Vancouver. > > -----Original Message----- > From: [email protected] [mailto:[email protected]] > Sent: April 15, 2002 4:49 AM > To: [email protected] > Subject: question on measuring bonding impedance > > > Is there a standard method for measuring AC bonding impedances for > electrical bonding? > > Thanks in advance, > Susan Beard > > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Ron Pickard: [email protected] > Dave Heald: [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://ieeepstc.mindcruiser.com/ > Click on "browse" and then "emc-pstc mailing list" > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Ron Pickard: [email protected] > Dave Heald: [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://ieeepstc.mindcruiser.com/ > Click on "browse" and then "emc-pstc mailing list" > ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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