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differential amplifier tech Answered

Hello, I'm following a circuit diagram for a current monitor that uses an op-amp as a differential amplifier. Connected to V- and V+ on the amp are the positive and negative leads of a 10mH Inductor that senses the current (as much as 9A) passing through an insulated positive line. The gain on the op amp, I'm told, is 220. If I calculated this correctly then at 9 amps in the insulated wire, 0.09V should be produced by the inductor and there upon entering the V+ lead and -0.09V in the V- lead for a differential of 0.18V which gets amplified to 39.6V. However the voltage source that powers the op amp is only 9V. So question # 1: Did I break down the math correctly? question #2: What happens to the excess voltage from the gain? I am getting all of my op amp information from wikipedia. I've never used an op amp successfully before.


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13 years ago

. You should be able to adjust the dropping resistor across the coil to get the desired input V to the op-amp. Or adjust the gain of the op-amp. . Do NOT hook the coil straight to the op-amp. You have to use a dropping resistor.