Static discharge

[Anonymous]

I have noticed that you can get varying degrees of static discharge from the type of plastic housing that I use for the coils that I make.Does any one feel that this static can interfere with the performance of the coil.
Regards Frank Wallis

 

[Anonymous]

Hi Frank,
I have never noticed that the detection performance of a coil is affected in any way by static charge. I have dealt with many industrial applications where you have a plastic conveyor belt moving over a polythene coil housing which induces higher levels of static than you are likely to get in the field. The only effect that static can have is when it discharges to something and you get a spark. This can cause a momentary false signal which gives a bleep in the phones. However, this cannot be confused with a genuine signal as it does not repeat, as when you scan a target. Also, there is no build up to the signal - it is just suddenly there.
Eric.

 

[Anonymous]

Hi Eric
What concerned me was that I have read that if you can hear this discharge,the voltage can be in the area of about 2000v.When detecting this discharge can sound very much like a target,which does not have to be directely under the coil,as you sweep past a target,you can get this beep.Here in victoria most people are listening for deep targets,as small peices are getting a little bit harder to find,that is one of the reasons that I raised this point.Which type of housing produces the least static discharge. I have had the feeling for some time that when you place coil in the housing that you get a slight decrease in sensitivity.
Regards Frank Wallis

 

[Anonymous]

Hi Frank,
My experience is that the static discharge is often inside the coil housing. A charge builds up on the plastic and then discharges to the nearest internal conductor, which is usually the coil shielding. The resulting pulse of current in the ground circuit of the electronics gives the false bleep. Some housings (some Whites detectors) use a conductive plastic which disperses static in addition to acting as a shield. You can also buy antistatic fluids which can be wiped or sprayed on to the outside of the coil housing.
Certainly with PI detectors, there is no evidence that I know of, to indicate that the performance of a coil is any different in, or out of, its shell. The only problem I had once was when the potting resin supplier used ground up pumice as a lightweight filler. The resin itself gave a magnetic signal!
Eric.

 

[Anonymous]

Hi Eric
I use electrical conduit for housing of the coil,and the orange type that they use for under ground is much more prone to give off the static discharge than the grey type.This accures from time to time when you brush twigs and bits of grass and such.I found that you can over come this by wrapping it with teflon tape and then covering over with a stronger tape.Many thanks for your thoughts on the problem.
Regards Frank Wallis