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Part Number: TL082
I am using a TL082 JFET input dual op amp as two difference amplifiers with a single supply of +24V. The first amp has a gain of 1 and an offset of 1.5V and it works fine. The input voltage to this amp comes from across a sense resistor fitted in a 4 - 20mA loop circuit . The output of the first diff. amp feeds into one input of the second diff. amp, and the other input of second amp connects to a the voltage divider setup that is adjustable by a pot. The gain of the second amp is 2.5 and its offset voltage is 0V. I have no trouble getting the full-scale output when 20mA flows through the loop circuit . The problem I have is that for input current of 4mA, when I adjust the pot to calibrate the amp to go to zero, I cannot produce a 0V at the output. The lowest output voltage that I get is about 1.5V. I tried simulating the circuit using the TI's op amp model for TL082 and I got the same result. Do I need an offset to the 2nd amp in order to drive it to 0V?
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Regards,Ronald MichallickLinear Applications
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