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i would like to make a current sensor which could detect current flowing in aplliances from a distance of about 20cm? Answered




hi, U can use current tansformer to sense current flowing in a wire...

How much, or just the fact it is ? 


Well, detecting AC current is mostly a matter of picking up the magnetic field from the AC current. Any good hardware store should have a detector which will work within a few cm; it's basically just an antenna-coil circuit which resonates at 60Hz (America) or 50Hz (Europe) and a small amplifier which responds to that signal by turning on a light and/or a beep.

It's possible to construct a more sensitive version of that. The problem then is that it would tend to pick up current flowing in other nearby wires. Making it more directional might be something of a challenge, but should be doable. There's a system that electricians use for tracing AC wiring through walls which does essentially this -- but in order to distinguish one wire from another, it modulates a higher-frequency signal onto that one line. (The solenoid in the circuit breaker generally keeps that signal from escaping onto other wires.)

All of that works fine on wires. Appliances may have steel bodies which might block a lot of the field. The professional tool I mentioned does work through conduit and BX shields, so "if it happens, it must be possible"... but again, that uses a different frequency, which may make a difference.

If you could tell us what you're actually trying to do with this information, we might be able to suggest other solutions.

Actually I am thinking of doing it as miniproject at my college. My basic thought was to detect the current flowing in the higher appliances through which we could avoid necessary power wastage as we would forget so times leaving it switched on. There should be some kind of alarm such a thing which we would be reminding us of it.
Then i came across a circuit in which a transformer was used in which a primay was kept open which would detect the current flowing through the circuit and which in turn was connected to an OP amp from there to an timer IC which was connected to buzzer. So as soon as the circuit was switched on the buzzer would get active for every 15min of course the time period could be changed. But how could a transformer detect the current flowing in an appliances and get activated?
The appliances are usually made up of some kind of material which would be preventing the peneteration. So is it possible for the transformer to detect it in an " appliance" and operate??