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Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Hi Lads and Girly Whirls,
I have a Japanese 1990's (at a guess) TR880! megohm meter, which goes right up into the T-ohm range.
Everythig is clear and simple up to, say, 1T, but beyond that it seems to me that special rules must be devised.
How shall I measure the resistance of a piece of PTFE, or the trans-glass leakance of an X-ray tube? What contacts must be made? At what point must I put the material to be measured in a die-cast metal box with impedance matched ins and outs?
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
A related measurement is the input current into electrometer amplifiers, in the fA range.
National Semiconductor have a guy called Bob Pease, very old skool, he writes a lot of their analogue application notes, one is on the topic above. It gets into the nitty gritty of cosmic ray ionisation dumping charge on electrodes. It's not exactly your app, but worth a read anyway. The articles you want are the "what's all this teflon stuff?" and "what's all this femtoamp stuff?".
While you are searching there, most of his other stuff is worth a read.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Thanks for your vacuum idea, Aonomus. I will ask my pal "Plasmatron" what he thinks, though in all candour, I think we might have chatted over the matter by now.
Slackman, fA is certainly what we are talking about here. I'll look up your reference to Pease. Thank you.
Registered Member #505
Joined: Sun Nov 19 2006, 06:42PM
Location: Yorkshire!
Posts: 329
Dr. Slack wrote ... ...National Semiconductor have a guy called Bob Pease...
I've seen Bob Pease present at a NS seminar in Manchester and he was amazing, he just blew the other presenters away. Everyone else was there with Powerpoint slides but come Bob's turn he turned off the computer and wheeled out his OverHead Projector "Analog Powerpoint" and proceeded to draw most of his slides freehand.
Registered Member #2123
Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312
Bob Pease single-handedly took on Taguchi on Toguchi's Theory of Optimization concerning circuit design optimization and won, getting Taguchi to write that he was not concerned with actual results, only the optimization proccess. Pease also took the wind out of the sails of 'Fuzzy Logic'.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
Keithly has some good app notes on the subject, check out the manual and literature for the 6517 which goes into taking T ohm measurements.
Does your meter have a guard terminal? All applications capable of such measurements use a guard to eliminate the leakage from the leads to the object, which greatly eases the equipment design.
Registered Member #2123
Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312
Use of low-tribolelectric effect triaxial cable and triaxial connectors (see picture) are recommended for stable measurement of femtoamp currents (how many electrons comprise one attoamp?).
My (old) Keithly 619 uses triaxial connectors, it is only capable of measuring gigohms.
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T-0hm measurement techniques
