Hello,

We are using a 34980A multimeter with a 34922A 70chanel multiplexer to make 4-wire resistance measures.

We are getting some negative readings for the resistance measures. We are taking measures through a bed of nails fitxture so we use pins con connect the multimeter with the DUT.

We tried to connect all the 4 pins involved in the measures with a conductive piece of cupper but we get also a negative value. And if we decrese the temperature, the resistance becames positive.

I'm not sure of what should happen, but for sure, negative resistance is not possible.

Does anyone faced the same problem? I read in onother topic (+DMM Measuring negative value+) that it should be a firmware problem...

Thanks for your help.

Francesc

We are using a 34980A multimeter with a 34922A 70chanel multiplexer to make 4-wire resistance measures.

We are getting some negative readings for the resistance measures. We are taking measures through a bed of nails fitxture so we use pins con connect the multimeter with the DUT.

We tried to connect all the 4 pins involved in the measures with a conductive piece of cupper but we get also a negative value. And if we decrese the temperature, the resistance becames positive.

I'm not sure of what should happen, but for sure, negative resistance is not possible.

Does anyone faced the same problem? I read in onother topic (+DMM Measuring negative value+) that it should be a firmware problem...

Thanks for your help.

Francesc

With this parameter activated we have a faster response to the temperature changes and the system does no get too negative values. Even that we still have some negative values.

One of the test we made was making a short directly in the Terminal block between all four connections of a 4W channel. Reading the value on that channel we get a negative values in both cases (Offset compensated or not). If we increase the temperature of the terminal block we get negative increases of the resitance and if we cold it down we get positive increases of the resistance

Is there any document that explains the method of 4W measures used by Agilent. WE can not understand exactly how, but it seems that Voltage and Amperage measures are not taken at the same time. So if resistance is changing along in time (due to temperature changes) can lead to strange results.

The 34980A does not measure the current source for resistance measurements. It is a precision calibrated current source of known value that is stable over the .

I was not able to see any negative readings with a short although I didn't vary the terminal block temerature. I do see that if you change the current source polarity, it will read negative resistance. I think this is intentionally done so that you can see the polarity of the current source.

The accuracy for values of 1 ohm or less is +/- 0.004% of the range, so for the lowest 100 ohm range, it's +/- 0.004 ohms for temperatures in the range of Tcal +/- 5 C. The temperarure coefficient is 0.0005 ohms/C outside that range.

I'll look into this some more.