I am using AD7193 to measure the resistance of a RTD. The RTD is in series with a reference resistor. I use ratiometric 4-Wire configuration to measure the resistance. The resistors are powered by AVDD and are connected to the Bridge Power-Down Switch. The circuit seems to work fine.
However, I also need to measure the voltage from a strain-gauge (Wheatstone bridge). I also power the strain-gauge with AVDD and connect it to the BPDS, so that the RTD and bridge are in parallel. I realized that I get different values for the resistance of RTD when the strain-gauge is connected. Typically, the 4kohms RTD changes by 15ohms when I connect the strain-gauge. The equivalent resistance of the strain-gauge is 1kohms.
Also, I get different values for the RTD when instead of using BPDS, I directly connect it to Analog Ground (typically 10ohm difference).
Could you please help me understand this problem ?