ROOSIE Posted January 14, 2017 Share Posted January 14, 2017 I'm trying to build a Instrumentation amplifier that would do a 10uV -> 10mVamplification. The motivation is to measure uA currents on a small enough shunt resistor (1-10Ohm). For a proof of concept, I've built a circuit like the one below(png1.)with a distinction that I'm powering it with two 9V batteries and am using LM2902N as the op amps and Rg is somewhat different. It has much less that the required 1000x gain. However, when measuring the results for different input voltages, the gain seems to vary: png2. I was expecting it to be constant. · What is a reasonable place to look for the causes of the variations? · Cheap resistors? · Inadequate op amp? · Breadboard prototyping? · 2x9V batteries as power supply? · other? Quote Link to comment Share on other sites More sharing options...
Greg Oshiro Posted January 15, 2017 Share Posted January 15, 2017 Roosie-- How is the gain measured? is this AC gain or DC gain? If you have access to an oscilloscope, does the output signal look like the input signal? A drawing of the measurement setup would be helpful. Quote Link to comment Share on other sites More sharing options...
efzauner Posted January 16, 2017 Share Posted January 16, 2017 your mid range input voltage is 25mV. I am presuming this is RMS. . if you gain was designed to be 1000, then you are asking it to output 25 volts...RMS this is like +/-17V peak. Are you sure you are not hitting the DC rails? Unless your X axis is marked incorrectly... are you inputting mV or uV? Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.