How to read accurate measurement on resistor using HP34970A via GPIB

[Labview Resistance Measurement]

I tried to measure resistor value fixed on PCB using HP34970A via GPIB and labview7.1. The result is fluctuated and not constant if the resistor is above 100ohms. Any one can help me to solve this problem? Thanks!

[PhillipBrooks]

I suspect that your problem is related more to technique than to LabVIEW and GPIB. If you're using probes or mini-clips on a surface mount resistor, the contact resistance is most likely the problem.

For some tips on how to make accurate measurements, look at http://ietlabs.com/tech/index.html.

[Labview Resistance Measurement]

Thanks Phillip!

However, it is not problem from cable. I run the labview to measue the resistor ( 1.5kohms) stand alone (not soldering on PCB) and it gave me the correct value.

Any suggestion else ?

Thank again,

VT

[BrianInTheForest]

A resistor by itself will get a different reading then one on a board.  Is there anything in parallel with the resistor?  A 4 wire resistance measurement is more accurate then a 2 wire resistance measurement.  I use the 4 wire measurement across a 10 ohm resistor using the same meter as you.

Brian

[AnalogKid2DigitalMan]

Do you have another meter available to manually measure and verify the resistance across the device while it is in-circuit?

[Dennis_Knutson]

What other types of components are on the board that are in parallel with the resistor you are trying to measure? Any capacitors, inductors, etc? These can all affect the reading. What happens if you measure the resistance with a different DMM or the 34970 in manual mode? If the reading is as expected and stable, are you using the 34970 in scan mode? You may need to slow the scan speed way down or not use scan mode at all. Command the relay to close, pause, then take the reading.

[PhillipBrooks]

A 4 wire measurement would be best, the meter will maintain constant voltage/current through the component and help isolate the other components from the measurement.

When using autorange, many meters will return a transitional value; check that it's not an autorange issue by measuring twice and looking at the second value returned. I generally configure any meter for the nominal value before measuring. Some meters will take a long time to autorange and you may get a VISA timeout waiting for the instrument to return a large value indicating an open.

The choices are
    Config meter for the expected value (manual ranging)
    Trigger, wait and measure with autoranging
    Autorange and measuring twice (discarding the first value)