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Kelvin Varley Divider with Analog Switches/Muxes

Discussion in 'General Electronics Discussion' started by hatimbt, Aug 6, 2019.

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  1. hatimbt


    Aug 6, 2019

    I'm trying to build a Kelvin-Varley Divider network to have precision voltage dividers. Can I realistically use Analog Switches/Muxes to tap the resistors at each decade. I know that when they make precision KVDs, they have to use very low resistance rotary switches.

    Does anyone know how to calculate the acceptable maximum ON/contact resistance for the switches?

    I'm most likely going to be using the 10K, 2K, 400R, 80R 16R decades.
  2. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    Where are you from? Are you an expert in electrical metrology? What kind of calibration standards do you have on hand to verify the accuracy of your DIY Kelvin-Varley Divider network?

    Since the stages in a KVD are cascaded, resistance errors accumulate quickly. In the Air Force, we used manually switched decades for our KVDs, with the last stage being a wirewound potentiometer. Rotary stepper switches, with gold-plated wipers and gold-plated fixed cotacts were used to implement a KVD in our automatic test equipment. I don't know how low, or how repeatable, the contact resistance was, but these were only four-decade KVDs. Your mileage (or kilometers) may differ.

    Analog switches are cheap enough that you should be able to throw together a KVD based on them and then test it to see if it has acceptable performance. BTW, what exactly are you going to DO with a KVD? How will you know how accurate it is? How will you excite it? Will excitation cause it to heat up and change its division ratio?
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