I want to measure current in 220V ac line. My load will be above 40 watt. ACS712 and CT(current transformer) both are able to measure the current. I want to measure the current and want to get it in arduino.So which one will be better for me? Thankz in Advance.
The ACS712 requires you to 'break into' the 220v line so perhaps not the safest method. The CT method is probably the best from a safety point of view but getting suitable resolution may be a problem as the usual lowest range model is around 5 amps. But you are looking at measuring 40 watts (volt-amps ?) at 220 volts which is only around 0.18 amps. However, if you can wind say 10 turns of your line cable through the CT loop then it effectively becomes a 0.5amp CT so might suit your application.
Since the signal is an AC one you also need to work out how to measure ac with an arduino. The following link might be useful as it shows how to bias the AC signal to ensure you do not apply negative voltages to the arduino input
https://learn.openenergymonitor.org/electricity-monitoring/voltage-sensing/measuring-voltage-with-an-acac-power-adapter?redirected=true
Trust this helps