Author Topic: Why is a LR-700 AC resistance bridge showing negative resistance?  (Read 866 times)

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Offline geoyumzzzTopic starter

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I have a Linear research Inc. model LR-700 AC resistance bridge which is the benchmark for resistance measurements. However, for some reason, the metallic thin film sample that I am currently measuring is showing a negative resistance.

Some more detail, even though I don't believe the sample has any inductance, the LR-700 measures about -400 Kohm reactance (mutual inductance). This -400kohm reactance is measured in the resistance range of 2 Mohm. I believe that the resistance range is coupled for measuring both the resistance and the reactance. Hence, the lowest measurable resistance in the 2Mohm range is 10Kohm. I observe that the resistance value goes negative after reaching this value of 10Kohm, which might mean that the resistance value is out-of-range, but since the reactance value is still in the 2Mohm range, the range remains at 2Mohm. I am unable to find any information about the negative resistance measured by a LR-700 AC resistance bridge. I am wondering if anyone has also encountered a similar problem or figured out how to interpret a negative resistance measured. I would be immensely grateful if someone can help me understand this. Thank you.
 

Online bdunham7

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Re: Why is a LR-700 AC resistance bridge showing negative resistance?
« Reply #1 on: February 02, 2021, 11:05:53 pm »
Do you have the manual?  (Just asking...)

Does the unit appear to work properly with other resistive samples?

Exactly how is the thin film sample mounted and connected to the bridge?  Is there any chance that the sample (as connected) is capacitive or has capacitance to ground?
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 


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