ADC input using a current transformer?

[mister_e]

High likely you'll need at least to load your current transformer, do a search for Burden Resistor, there's a load of discussion/appnote all over the web.

http://www.coilwinder.com/current_tr...and_theory.htm
http://www.datatronics.com/pdf/curre...se_article.pdf
http://powerelectronics.com/mag/powe...t_transformer/

Probably not a bad idea to buffer the signal with an op-amp as well.

Not sure of the defaut DEFINE parameter for ADCIN, but you might need to include them to reach better results, or not use ADCIN and set/read PIC regsiters manually.... which is the method i prefer, but it's me

HTH

[Tom@Nottingham]

Hi

If you are using a 600/5 amp ct, this is intended to measure up to 600amps?
The output then usually passes through moving iron panel meters and heaters/relays to protect large a.c motors etc. This works fine as the meters are passing good sine wave currents and the heaters work the same no matter what the wave-form looks like. I assume you have wound many turns of your motor through the centre of your ct.

I have been trying to measure rms current using a ct but with limited success.
Since a dc output is required, the bridge I made was from 4 IN4148 diodes as these have low forward voltage of 200mv? The output from the bridge was then fed through a resistor(variable 0-100k) to a/d input and any capacitor 1 to 100mfd together with a resistor to ground etc .

This should work fine providing you are using constant smooth sine wave currents. If you have any noise, sudden load changes or are thinking of using a triac/thristor to vary fan speed etc. then strange readings appear. This is due to the bridge rectifier measuring peak volts not root mean square. Induced voltage in the secondary of a transformer is proportional to the rate
of change of current in the primary. It is not easy to measure accurately a.c current, unless using hall effect sensors and and integrating wave-form etc.
This should I think also be possible with ct output by biasing 1 output with 2 resistors to mid-point of a/d input and other output to actual a/d input,
or 2 a/d inputs (like op amp differential inputs) one for each ct output. Suitable load resistors/capacitor/ zenner diodes required. Then busy job for Pic converting to rms? or may not work? not sure.

Hope this helps

Tom