Vasile Surducan wrote: > On 3/4/08, Michael Cunningham wrote: > >> I am rather new to PIC development but I am learning fast. I would like to >> build a circuit to measure the amount of AC current in AMPs flowing through >> a wire. Any suggestions on how to measure the current without directly >> connecting to the wire which will be carrying up to 125vac @ 30 amps. >> >> Can the PIC ADC be used for this purpose? Eventually I would like to drive an >> LCD with the value in amps. >> >> Any suggestions on where to begin? >> > > See what error do you want for this measurement. The hall effect > sensors are good as "indicators" and not for precise measurements over > the full temperature range. If 5% is ok for you (1.5A error at full > scale), go with hall, but if you need a more accurate measurements go > with precision transformers. > > Vasile > This really depends on the waveform, Some time ago i built a power monitor using a current transformer and resistor as load i picked the resistor to give areasonable voltage span for the PIC ADC and i connected the other end of the winding to V/2. This mostly worked very well but i not for an asymetric load. When testing after i first built it, i tried various loads and all was well until i tried a power drill, which at low speeds only uses one half of the mains cycle. Because the average voltage out of the current transformer is zero the zero part of the waveform gets shifted below zero. This obviously affect RMS calcualtions. I guess one solution would be to have a very high turns ratio and use an opamp configured to convert current to voltage. PS I'm sure the LEM ones are nearer 1% -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist