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Old 8th November 2007, 12:14 PM   #1
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Default Surface resistance measurement

OK, here's a pic of my attempt to construct a probe for surface resistance measurement.

Click the image to open in full size.

The range of the Megger in the picture is 100G Ohm (1.10^11) and the surface resistance that I want to measure should be in the order of 10^11 to 10^14... not compatible.

The probe consists of a strip of insulating material and two strips of copper tape. Now if I understand the definition of ohms/square, then the probe that you see in the picture should give an 'amplification' factor of about 40 (150mm length and 3.7 mm spacing between the strips). Right?

Measurement of a Nylon coating with 2.5KV on the probe shows a reading of 2x10^11 to 5x10^12 ohms/square, which is in the range that one would expect for a this coating.

Now before I start cheering, does anyone see a problem or fault with this probe/measurement?
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Old 8th November 2007, 12:29 PM   #2
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Is that a two-terminal probe? If so, there can be inaccuracies because of surface contact issues- a four-point system is optimum.
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Old 8th November 2007, 12:34 PM   #3
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Maybe have a look into Van der Pauw resistivity measurement technique. That's four point and involves passive currents so you don't need to rely on the meter having any crazy ohms ranges. I bonded fine wire connections onto the sample using conductive paint.
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Old 9th November 2007, 08:50 AM   #4
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Thanks gentlemen,

yes this is a two point probe, I did not know about the four point probe measurement so I had to look it up. Agreed, that would be the way to go for good, reliable SR measurement.

For ballpark measurement this 15 minute probe and $50 Megger seem to work ok-ish thow, even in the 10^12 range.
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Old 25th November 2007, 03:33 AM   #5
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Default Resistivity Measurement ...

arend-jan,

Look at the Keithley Instruments website, they have papers about resistivity measurements with reference to engineering standards.

Their technique uses a high voltage power supply, a resistivity
jig with defined geometry, and an electrometer ...

Sounds like a lot of equipment, but the papers may be useful ...

Good Luck !
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