Electronics Forum / Electronics / May 2008

Hi Phil,

Thankyou for your reply to my question even though it wasn't explained
adequately. I will give you as much information as I possibly can so you
understand the application.

It is for my own basic pulse induction metal detector and works as follows.

It starts with a squarewave pulse of 24v, 1ah from the the detector box to
the coil. While the pulse is on the power goes to the coil. When the pulse
is switched off, the field collapses using resistors (3w metal film) across
the coil.
The next part is the critical part. The field created by the coil has to
collapse at a certain rate. If it collapses too quickly or too slowly, the
sample is taken at the wrong time, so incorrect.

Now, unfortunately I don't have any test equipment to know how much
resistance I need across the coil to see the point at which the sample needs
to be taken.
So, I thought I may be able to use trial and error and adjust the
Potentiometer while using the detector, then use a multi meter to read the
value from the Pot to determine the value of the resistor I would need
across the coil.

But now I think this may not work because the Pot creates its own inductance
and capacitance.

Any suggestions as to how I could do something similar with a rheostat or
pot? Would the one suggested below still work for this?
Would a cheap wirewound pot work if I used a shielded cable and mounted it
away from the actual control box?

Thanks again!