Coil question for anyone .

[Frank-S]

On a low power pi there is a resister in series with coil, if the restance is lowered will
it increase dept,also will it damage detector.thanks.

 

[Reg]

The short answer to your questions are yes, yes, and yes.

The long answer:

There is a resistor in series with the coil. That is how the coil current is reduced. Also, the PI uses a low power FET to drive the coil. So, reducing the series resistor could allow too much current which could damage the FET. Reducing the value of the series resistor can increase the depth a little, but don't expect much. In fact, in many cases, it won't be noticeable because it takes a fairly significant current increase to see any change. Worse yet, it could affect the minimum delay you can obtain.

The bottom line, all of the above issues are intertwined and have to be looked at carefully before making any changes. Otherwise, if you are not very lucky, you could let smoke out of your detector and that means those parts that let the smoke out have to be replaced. The pc board on which the components are mounted is a no smoking board and doesn't take kindly violations of its policy and most likely will retaliate by electing to stop working.

Reg

 

[Frank-S]

Thank, Reg.
another qyestion,I have opeaned a fue coils.some coils have a metalic paint for
shielding what do you call this paint and where can you get it.

 

[Reg]

Frank,

Most manufacturers are using a graphite mix paint that is probably developed to their specs. You might go over the the Geotech forum and see what people are using or making. Personally, I can't recommend any specific paint because I normally don't use that technique for shielding, but may in the near future. The Geotech forum has a lot of information about building coils for a PI. Here is a link to that forum:

http://www.geotech1.com/forums/forum.php

Getting the right resistance is somewhat critical. Too little shielding and you have problems with the detection of plants and other undesireable things. Too much shielding and you reduce the sensitivity.

The shielding needed on a PI coil is different than that of a VLF and probably varies even from a low PI to a high powered unit but I don't know for sure. I suspect what works on a high powered coil will work on a low powered coil, but not necessarily the opposite. Keep in mind this is a guess on my part. What I do know is it takes a fairly low resistance to properly shield a coil.

Some manufacturers use a graphite covered paper for shielding and if I remember correctly, the resistance was about 40 ohm per inch, meaning when measured with an ohmmeter the resistance will be 40 ohms with the probes 1 inch apart. So, if I were going to use this type of shielding, I would initially try for some resistance similar to begin with.

Reg

 

[Frank-S]

Thanks
Every time I try geotech 1 , answer all questions it dont work for me.
they make it two difficult to get in,years ago it was easy.
to many questions

 

[Reg]

Frank,

If you answered all the questions, then you should receive an email from the Geotech forum. You have to validate your request to join by responding to that email. Are you doing that ?

Reg

 

[Frank-S]

IT dont work,findmall has a better system.I will wait a
week and try again.