AnsweredAssumed Answered

Problem with gain setting on AD623

Question asked by hlbralower on Jan 12, 2012
Latest reply on Mar 17, 2013 by rafp

Hi all,


I'm trying to amplify the voltage across an RTD with the AD623. I have a nominal 100 ohm RTD attached to a 5.62kohm pullup resistor at +5V. The other side of the RTD is attached to ground. The voltage across the RTD is fed into the noninverting input of the in amp and the inverting input is grounded. The in amp is powered at +5V/0V, and the reference input is also grounded. All the power rails and ground rails in my system are tied together, and the rails are all decoupled at several points on my board with 0.1uF caps. I expect the maximum input voltage to the in amp to be slightly less than 0.1V and I'd like to amplify that input as close to the 5V rail as possible, so I'm using a precision 2kohm resistor to set the gain on the in amp to 51. However when I turn the amp on I see an amplification of only about 14. I tried plugging in smaller gain-setting resistors to increase the amplification but this barely changed the output. Any suggestions as to what I can do to fix this problem? Thanks for your time, and I look forward to hearing your ideas.