April 15, 2004

Ohms, continued

To recap, I found an 18 MΩ resistor that I decided to use to scope out the Keithley 6430. I made two 2-wire measurements, with offset compensation (OCOM) disabled (17.7025 MΩ) and enabled (17.7084 MΩ). Next up, 4-wire measurements and other variations...

As a sanity check, I redid the two measurements (machine cold) from yesterday.

measureR (MΩ)
2-wire, no OCOM17.7057
2-wire, with OCOM17.7048

Not very encouraging. It is unclear how long it has to warm up before the readings are consistent? It may also be due to the temperature of the resistor. After about 5-10 minutes the OCOM measure is now 17.7056 MΩ. It has been about an hour now, here are the measurements.

measureR (MΩ)
2-wire, no OCOM17.7057
2-wire, with OCOM17.7047

Maybe I did something funny yesterday. Here's the setup for the 4-wire measurement:

4-wire.PNG

I'm not sure why the diagram has the Sense LO going all the way back to the rear panel connector. Wouldn't it be sufficient to use the Sense LO from the pre-amp? Since I didn't have a banana plug cable handy, I used a triax to BNC followed by a BNC to clip leads. Something funny... I setup the four-wire measurement and am now getting 0.51274 MΩ. Weird. Without the sense wires, I get what I got before (whew... didn't break anything.) What went wrong here? Ok, I think I see the problem, I think it is the triax-to-coax connector. Instead of taking Sense HI and Sense LO out, it is taking Sense Hi and the shield.

triax.PNG

The 6430 comes with one 6430-322-1A triax cable which is terminated with a triax connector on one end and booted alligator clips on the other end. Why just one? What I really would like is another one of these for the sense side.

On another note, I notice that whenever I hover around the measurement the reading gets noisy - static? capacitive-coupling? Be careful.

Posted by torque at April 15, 2004 10:14 AM
Comments

You want to be an auto mechanic?

Posted by: Sonja at April 15, 2004 11:09 PM

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Posted by: Lead Generation Software at December 7, 2006 5:39 PM
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