Connecting HP 4140B pA Meter for VI Curve Measurement

[seang]

Hi, I'm trying to make connections with a pA meter / V source. It is a HP 4140B. Let's just say I'm going to try to find the VI curve for a resistor.

The voltage source is coax out. I think I know what connections to make here but could someone help me anyway?

The current in is via triax. I've never worked with one of these. What connections do I make?

Thanks for your help!

 

[berkeman]

I don't know if it helps, but here are some Agilent Application Notes about the 4140B.

http://www.home.agilent.com/agilent/facet.jspx?kt=1&cc=US&lc=eng&k=4140B

It was discontinued in 2000, and I didn't see the manual at the Agilent website, but I only took a quick look. Do you have the manual? You can probably find it on the web somewhere.

BTW, what does pA stand for?

 

[f95toli]

pA=picoamp, 10^-12 A

 

[berkeman]

pA=picoamp, 10^-12 A

Oooohhhh. Thanks.

But why in the world use a picoAmmeter for making a VI trace of a resistor? Sounds like a square peg headed for a round hole... ?

 

[Topher925]

Oooohhhh. Thanks.

But why in the world use a picoAmmeter for making a VI trace of a resistor? Sounds like a square peg headed for a round hole... ?

Hes probably measuring a high impedance component.

 

[seang]

Oooohhhh. Thanks.

But why in the world use a picoAmmeter for making a VI trace of a resistor? Sounds like a square peg headed for a round hole... ?

Ha, not actually going to perform that experiment. Just needed an example. In reality I will be measuring VI curves of some films, CNT samples, etc.

btw, if you google HP 4140b, the first link is the manual. There are some figures in there that I suspect are useful, but I can't quite make sense of them.

Thanks for your replies

 

[berkeman]

btw, if you google HP 4140b, the first link is the manual. There are some figures in there that I suspect are useful, but I can't quite make sense of them.

If you have specific questions on figures in that pdf, post them here and we'll try to help out.

http://www.home.agilent.com/agilent...US&lc=eng&ckey=588221&cname=AGILENT_EDITORIAL

.

 

[seang]

on page 3-42, the setup shows the triax connected to GND, LOW, and HIGH (I think). If I'm measuring a two terminal device, what do these mean?

 

[berkeman]

on page 3-42, the setup shows the triax connected to GND, LOW, and HIGH (I think). If I'm measuring a two terminal device, what do these mean?

Interesting. It looks like they are guarding the high line with the "low" shield to try to have as little voltage difference between the high line and the surrounding shield, to minimize leakage currents. If they just had coax, then there would be the full voltage drop from high to ground between the two conductors, so that full voltage drop will drive a larger leakage current.

This technique is often called "bootstrapping", and is usually done to reduce the effective capacitance between a sensitive line and its surrounding shield. The shield is driven with an opamp buffered version of the inner conductor voltage, so the shield is always at about the same voltage. That way, there is no effective capacitive loading between the inner conductor and the shield -- the opamp is taking care of "bootstrapping" out the effective capacitance.

So make your connections to your 2-lead device as shown on page 3-43, depending on whether you DUT is grounded or floating. Does that make more sense now?

 

[seang]

Yeah, I think I get it. Sometimes you just have to talk it out I guess.

Thanks a lot for your help.