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AD5252 resistance output increases non-linearly


   I'm trying to provide variable resistance output using AD5252( 1K Variant) to a third party device which can read the resistance output using voltage divider bias. What is the issue was I can able to see the resistance output accurately(using multimeter across B1 & W1) which was expected when no third party device connected. 

But, While connecting with the third party device, the resistance getting amplified. [Eg: If i write RDAC with step 24 with the initial error of 89 Ohms. I see (89+(24x4) = 185) ohms using a multimeter across B1 & W1. But after connecting the third party device, it reads around 205 Ohms]. The increase in resistance is not linear in nature. It increases with increase in each steps of RDAC.

What may be the reason behind this kind of increase in resistance if i connect B1 & W1 with the other devices?