Hello,
I want to detect a pulsing signal (0-12V) in a cable without actually breaking into it.
I'm thinking of using something like this.
The signal wire has a 12V dc supply cable and a 0V cable alongside it, which the current clamp would have to go around as well, as they're all molded together.
I know there's a lot to be said for just getting one and trying it, but can anybody tell me whether I'll be able to detect the pulsing signal with this arrangement?
Thanks 
No, if you clamp around the signal and the return wire the current clamp has nothing to detect because the net current through the clamp will always be 0.
Signal strength in that sensor is depend to the current not to voltage - 12V pulses with 1k resistor load give you every week signal, with 1 ohm resistor load may work.
1.Attach hall sensor to the cable.
2. Use mosfet transistor, make 5-10 turns wire around you cable one end connect to gate with pull up resistor
3. use relay coil
A small capacitive probe will need immediate buffering to a lower impedance, but with a very
low capacitance device (typical discrete MOSFETs may have too much).
With several wires in the cable and only one changing, the maximum pickup voltage will be small
and need voltage amplification too, not just buffering.
MarkT:
A small capacitive probe will need immediate buffering to a lower impedance, but with a very
low capacitance device (typical discrete MOSFETs may have too much).With several wires in the cable and only one changing, the maximum pickup voltage will be small
and need voltage amplification too, not just buffering.
electret microphone - disconnect microphone and attach the wire.
I was able to detect a hair movement from 10 cm
That's a neat idea. Electret microphones have a built-in high impedance buffer amp of course, for the same
reasons.