Electromagnetic field (AC current) detection

Thread Starter

kadriguler

Joined May 18, 2011
3
Can we make a simple but precise circuit that locates the hidden current (cable) on the wall ?

Circuits made with BC547 (3 pcs) transistors and CD4017 integrated circuit cannot detect the current inside the wall.
 

andrewmm

Joined Feb 25, 2011
403
Thanks
These circuits for surface cables, with a more sensitive circuit I want to find the cables inside the wall.
can you be specific as to how far in the wall and what sort of wall are you looking at ?

Its a compromise ,
The air is full of "transmissions" that will be received,
its a question of how sensitive the detector is, and how strong the wires magnetic field is.

the hall effect one works well to a wire carrying 240 volts, at about 1 amp through about 1 cm of plaster,

Advantage of the hall one is it has low sensitivity to the E field, whilst a typical single coil system does not.
 

Irving

Joined Jan 30, 2016
823
The problem with hall effect is it wont find cables in conduit and its not so good with twin and earth cables as the magnetic field around live is mostly cancelled out by that around the neutral.

A commercial cable/conduit finder uses similar techniques as a metal detector - a tuned circuit used in an oscillator is compared to a reference oscillator. When the first oscillator is detuned by the presence of metal the 'beat' between the two oscillators is an audio signal.

An alternative approach is to energise a coil as part of a moderate frequency RF oscillator. Eddy currents induced in nearby metallic materials cause a power absorption and a reduced output from the oscillator.
 

andrewmm

Joined Feb 25, 2011
403
I'm just wondering how they distinguish between AC on and AC off ?
An interesting problem this, wonder if anyone has taken a voltage detector apart , or designs them ?
 

Hugh Riddle

Joined Jun 12, 2020
23
I'm just wondering how they distinguish between AC on and AC off ?
An interesting problem this, wonder if anyone has taken a voltage detector apart , or designs them ?
I'm just wondering how they distinguish between AC on and AC off ?
An interesting problem this, wonder if anyone has taken a voltage detector apart , or designs them ?
Cable detectors normally sense the electric field around a cable, which is only present if the cable is connected to the mains (i.e. 'on') and not in a metal conduit. That field is strong enough to be cheaply detectable only because operating mains cables are (electrostatically) unbalanced (i.e. neutral near ground voltage, active at mains voltage).

Magnetic field detection isn't used to detect cables because cables create little magnetic field due to their equal active and neutral currents flowing in opposite directions, and would also require the circuit to be heavily loaded.
 
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