I am testing a buffer circuit. I came across a problem which i am not able to figure out why it is happening. Please help me out.
In a buffer circuit the input voltage is measured across a 120k resistor. The opamp used is ADA4522-2.
Case 1:- When a single DMM is used to measure the input voltage, a particular value specific to the current flowing is obtained. When the same DMM is used to measure the output voltage a difference of 20mV from the input voltage is obtained.
Case 2 :- When i use 2 multimeters simultaneously for the measuring the input voltage and the output voltage with their respective negative probes connected to ground, the difference in the multimeter readings has been drastically reduced to less than 0.1mV. In fact when both of them are placed simultaneously, the output voltage(which had a 20mV difference is getting automatically reduced to the same value as the input)
What may be the reason behind this? Why was the buffer giving a difference in input and output at the first case? How can the difference between the buffer input and output voltage be nullified?
Thanks in advance.