Thanks for the input. We were checking the standards every week, but are now shorthanded so I cut it back to bi-weekly. We did a simple gage R and R study earlier this year. R and R for the differential setup was 0.5 ohms, for the single-ended 0.1 ohm. In the absence of a real standard for differential, we could not check bias.  Louis Hart

-----Original Message-----
From: Craig Sullivan [mailto:[log in to unmask]] 
Sent: Wednesday, September 26, 2012 8:37 AM
To: 'TechNet E-Mail Forum'; Louis Hart
Subject: RE: [TN] Differential impedance standard

In a former life, we measured coupons for spc/reference daily for 28, 50, 100 ohm single ended, and 100 ohm differential.  Two weeks is a bit of a stretch in my opinion, because the scopes change daily based on temp/RH.  Not to mention, the cabling, static isolation components and probes all wear out. The contact points on the coupon also wear out. Add to that different operators have different techniques and end up with slightly different measurements.

Craig Sullivan
Manufacturing Engineer
MPL Incorporated
P: 607.266.0480 x115
F: 607.266.0482
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