Resistance Inaccuracies with DPOT (410-239)

[dwl]

Hi,

I'm controlling a Pmod DPOT (PN 410-239) with a raspberry pi.  I'm able to step the potentiometer through each of the tap points, measuring the resistance between the wiper terminal and the `B` terminal.  I can verify the resistance is as expected using a multimeter attached directly to the screw terminals.  When I connect 2 meter length of 22 gauge tinned copper wire to the screw terminals and measure the resistance between the wiper and 'B' terminals through this wire the resistance is significantly less. For example, at the mid-point in the range of a 10kOhm DPOT I see a resistance of 5060 ohms when measuring directly at the DPOT.  When measured through the wire I see 1900 ohms.  Why would the resistance be less when measured through the wire?

 

[JColvin]

Hi @dwl,

Could you attach a picture of your setup and how you are measuring it?

I was presuming your setup was akin to:

Multimeter Point 1 --> copper wire --> 'B' Terminal --> wiper terminal --> different copper wire --> Multimeter point 2

Which would be effectively just making your multimeter leads extra long. Such a setup would increase the overall resistance as, inevitably, the electric charge has a longer distance to travel and thus more molecules and irregularities to overcome. But you are reporting less measured resistance, which leads me to believe that I do not understand your setup correctly.

Thanks,
JColvin