Does anyone in this forum understand this circuit in more detail? What formulas does it work?
To what depth in the wall does such an assembly react, and how can I modify that so circuit increase the depth of penetration into the wall?
In this particular case, does this only depend on the diameter and length of the spool?
Coils make a magnetic field, not electric. They are used in metal detectors as conductors in the AC mag field
will have eddy currents, disturbing the field and thus affecting the inductance of the coil. The
circuit has to detect the change in inductance while providing an ac current to the coil.
You can also simply sense AC mains voltage with a single sense electrode - commonly wire / pipe/ trunking
detectors use both techniques together.
The wire, as the circuit shows, acts as an aerial, picking up the AC electrical field from the wiring in the wall.
The voltage induced in the aerial is amplified by the 3 cascaded transistors, this controls a large enough current to drive the LED and Buzzer.
Its probably sensitive enough, the gain will be more than a million. Too sensitive and the buzzer sounds all the time as you are holding the device. The fact that mains fields permeate the whole building will be the limiting factor to detection. Remember you are holding the device and being a second antenna that picks up field from all around you - all it can detect is a significant difference in field between where you are and where its antenna is.
The antenna is deliberately quite small so you can localize the signal and thus trace out the wire/pipe's path.
In my experience these devices have a sensitivity control so you can dial up sensitivity to the maximum useful level.
The wiring in the wall and all over a building is the equivalent of a RADIATING aerial, like a radio transmitter.
It emits an electric field around it like a radio aerial does.
The voltage and the frequency governs the range of the electric field and how easy it is to receive.
How deep into a wall do you want to detect electrical wiring?
Tom....
How deep into a wall do you want to detect electrical wiring?
I dont know.
I need for install a radiator and pipes (for drilling).
The wiring in the wall and all over a building is the equivalent of a RADIATING aerial, like a radio transmitter.
It emits an electric field around it like a radio aerial does.
The voltage and the frequency governs the range of the electric field and how easy it is to receive.
How deep into a wall do you want to detect electrical wiring?
Whether that only applies for buildings or and for homes (only more or less weaker)?
If it is an interior wall in the US, then detection should only need to be about 4". 1/2" thick wallboard, and 3 1/2" thick wall, before you reach the other side.
The fact that mains fields permeate the whole building will be the limiting factor to detection.
The wiring in the wall and all over a building is the equivalent of a RADIATING aerial, like a radio transmitter.
It emits an electric field around it like a radio aerial does.
The voltage and the frequency governs the range of the electric field and how easy it is to receive.
How deep into a wall do you want to detect electrical wiring?
And whether that only applies for buildings or and for homes (only more or less weaker)?
Is the photo not answering that question? Its not really a coil, they are just making the antenna wire have more
capacitance to its environment (making it effectively larger).
