However the datasheet for the AD620 says Input bias current max 1nA. As far as I understand, this means that ports 2 and 3 should not draw more than 1 nA, and should therefore have not significant effect on the measured voltage from the voltage divider. View AD620 datasheet from Analog Devices Inc. at Digikey

Feb 27, 2014 · I use ad620 for my load cell conditioning circuit. It amplifies load cell signal to +/- 10V range. I need to improve drift cause by temperature. When I apply just a little hot air to my pcb and output changes. I have ad620 with a gain of 660. I have +10V and -10V regulated from +/-15V. AD620 Instrumentation Amplifiers Analog Devices Inc. AD620 Instrumentation Amplifiers are low cost, high accuracy amplifiers that require only one external resistor to set gains of 1 to 10,000. These amplifiers feature 8-lead SOIC and DIP packaging that is smaller than discrete designs.