Sup,

I'm trying to read the voltage across a current shunt using an ADC. The current shunt is 50 milli ohms, so the voltage across it at its maximum (5 amps) should be :

V=IR = 5*0.05 = 0.25 mV.

Now this is far too small. My adc is calibrated to read voltages of 2.5 volts, so i need to use an amplifier to do it. My question is thus:
How would i wire it and what parts do i use?


Cheers,
JB

 

You could use a simple op-amp ampflier with a 351 or 741. You might have some trouble depending on whether you want to monitor the "high-side" current. There are special parts that can monitor high side currents and have an output voltage that is referenced to ground. This is usually better than monitoring current in the ground path.

 

This amplifier has a gain of 10 +-2% due to resistor tolerance. The output could have an offset as high as 10 milivolts. You can compensate for these fixed errors in the microprocessor.

Attached Images

GAIN_OF_10.jpg (9.1 KB, 540 views)

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Thanks, Russlk

That looks exactly like what i want. I'll try it out soon (in exactly how long it takes national semi to ship me samples of LMC6081. *cheap!*)

Cheers,
-- JB