Static Problems?

[Anonymous]

I have an email from a prospector in Arizona about the problem of static build up on his detector. This is not a problem that I have encountered in the field as we do not have such hot dry conditions in the UK. I have seen it on industrial detectors where you get a static build up on a conveyor belt passing over a coil and, rarely, it can be so serious as to damage or destroy integrated circuits in the electronics. The detector in question is an SD2100 with a Coiltek 14in coil and the result of the static is to give a loud audio signal every time there is a discharge. The obvious area where static is generated is the plastic coil housing which rubs on the dry ground. The charge can then be transferred via the shielding and the cable to the case of the electronics. Discharges can take place anywhere

 

[Anonymous]

The problem of electrical static build up is something that most people building metal detectors do not recognize. I used to use a SD2100 in Nevada and California and I realized that I was having this problem. Working together with Russ of Certified Detector Sales. We came up with a fix. Basically you make the metal detector and you the same electrical protential as the earth. To do this, you connect a very thin wire to one of the screws on the SD2100 control unit case. All screws on the case are connected to the circuit board's circuit ground. You then run the wire down along the rod assembly using electrical tape to hold the wire. End the wire at the top of the coil allowing a couple extra inches to connect the wire to the top of the coil by using conductive material. Conductive material looks like foam rubber and it is what they ship IC and other electronic parts in to prevent static electricity damage. You remove the rod from the top of the coil. Now place enough of the conductive material between the coil ears so that when you put the rod back on the coil. You will compress the conductive material. But first thread the end of the bare thin wire thru the conductive material before putting the rod back on the loop. Then you take another piece of bare wire and wrap it around your hand grip and connect the other end to a screw on the control unit case. This is so when you hold the hand grip. You will be the same electrical protential as the metal detector. Now get some antistatic spray and lightly spray the whole metal detector from top to bottom. Now take a ohm metter and measure the resistance from the conductive material to a screw on the control unit. If you did everything right. The resistance should be less then a 100 ohms. To ground your body to earth. You use a piece of 18 gage multistrand wire around 2 feet long. First strip enough insulation from one end so that you can wrap bare wire around your ankle. Then bring the wire down a long the outside of your boot. If you bring the wire down between your two feet you will trip on it. Adjust the length of the wire so that around 6 inches is touching the earth. Now strip off around four inches of insulation. Now the metal detector and you are grounded to earth. This change also allows you to hunt closer to electrical interference. Feel free is ask any questions.
Terry

 

[Anonymous]

Hi Terry,
Many thanks for the detailed reply. Looks like something that needs further investigation in hobby detectors. Your wire from the control box down to the coil also had benefits when working in water I remember. I have used anti-static spray on industrial coils but the effect wore off after a while and a respray was needed. What proved better was a sheet of grounded conductive plastic on the working face of the coil plate. For a hobby machine a coil cover of conductive plastic may solve the problem, or alternatively make the coil shell itself of conductive plastic. I have some Whites coil shells here and they are made of such a material, which also acts as a shield. You may not need the ground wire with such an arrangement as the conductive plastic may prevent static from being generated on the coil in the first place. You will notice that I have used "may" several times. Dealing with static is very unpredictable and what seems an obvious solution sometimes proves ineffective. I have read that hot, dry, windblown sand generates a high static charge of its own, which could be attracted to a conductive coil plate. Certainly the principle of trying to keep everything at the same potential is a good one to follow as you only get a spark when there is a difference in potential.
Eric.

 

[Anonymous]

Yes the anti-static "treatment" does wear off but it's cheap and availible for any machine. Also to conserve the spray Treat only the coil area as the rest is allready conductive.
The anti-static spray comes as different "strengths" I recomend staticide brand "heavy duty" part# 2005 as it has a better conductivity than most.
Russ
certified detector sales

 

[Anonymous]

Hi Eric, I used to hunt a fresh water swimming area that they would drain for the winter using a White Goldmaster V/SAT. In the morning, I could hunt with a sensitivity setting of six. In the afternoon when the winds come up. I could only hunt with a sensitivity setting of three to maintain a smooth threshold. It took me a while to realize that the wind blowing across the sand was building up static electricity. After doing the change to the Goldmaster. I was able to run with a sensitivity setting of nine. Found a lot of deep broken gold rings, ear ring backs and gold chains. But it was very hard to keep the wire from moving because the Goldmaster would sound off if the wire moved. I have felt that the coil cover should be made of conductive material. Also where you hold the rod assembly so you would be grounded to the metal detector circuit ground. Then I figured we would need special shoes built so that we would be grounded to earth. This would be safer then walking around with a wire tied to your foot. I do use both a wire on my CS-7 and my Excalibur to help reduce electrical interference here in Hawaii. I also coat the outside of the Excalibur control housing and battery pack with adhesive copper foil to help shield the electronics from electrical interference. I want my metal detectors to only make a sound when there is a target.
Terry

 

[Anonymous]

Hi Terry, Russ and all,
There is one aspect of grounding that you have to be careful of, particularly with PI. For a beach, shallow water or underwater detector, I never use a case that is grounded to the electronics. This is so with the Deepstar which has a metal case; it is intentionally left electrically isolated. Other detectors I make such as Beachscan and Aquastar have a plastic case with no external metal parts that are grounded to the electronics

 

[Anonymous]

Yes, I do know that the screw on the CS-7 battery compartment is not connected to the electronics. But it does work very well in making the CS-7 run a lot smoother. But I do admit that connecting a wire to a screw that does not go anything except the case does not make any sense. Some times you have to just be happy that something work and not drive your self crazy trying to figure out why it works. My changes on the Excalibur are not connected to the electronic either.
Terry

 

[Anonymous]

Hello Guys,
I'm the one that wrote the e-mail to Eric Foster about the static build up here in the hot arid Arizona Desert. I noticed in the Winter months the SD works excellent and cant complain about its performance. Although during the hot Summer months like now, the static is just overbearing. I understand that the wind and dry air cause the static to build up. Every so often when detecting, approx. every few minutes or so, the detector will discharge the static and cause a loud signal to be heard. I have tried using some of the static wipe pads that you use to clean computers, monitors, and such with, but it seems to wear off fairly fast.
A good friend which is a Physicist here in Arizona told me the same method that Terry explained, but it just seemed to difficult to ground yourself and the detector to the ground. It looks like it might be the only solution at this point and time. I really appreciate Eric posting the problem I'm experiencing here in Arizona, and thank all you for your help.
Take Care,
Robert Phx, AZ

 

[Anonymous]

Hi Gentlemen
Did you know that you can buy anti-staic shoes that will effectively connect you to ground via their conductive soles. i think however that the resistance is around 10M ohms so. This is allow satic charge to dissapate as apposed to jump down to ground. Used alot in the semi-conductor industry and are available from specialist industrial outlets as normal shoe styles. kind reagrds
Steve A

 

[Anonymous]

if I throw something out, then you can guarantee that I will find a use for it shortly after. When I moved premises I threw out some sheets of 1.5mm conductive plastic. They are what we used to discharge static from conveyor mounted PI coils and now that nearly all my work is on hobby detectors, I thought I would not need it again. Still, I remember the company that supplied it and it will be worth asking if they can make a coil cover of the material so that some tests can be done to see if it solves the problem. Incidentally, the conductive plastic does not affect the performance of the detector at all, as its resistivity is too high to cause any signal loss.
If I can get some plastic and make a cover of sorts, or even a disc that can be attached to the bottom of the coil, perhaps you would like to do some trials Rob?
Eric.

 

[Anonymous]

Hello Eric,
Thanks again for posting such informative information to help others. Here in Central Arizona, and I'm sure other States in the Southwest have the same climate conditions. Like I said before, during the Winter months temps. are kept under 80 degrees in the lower arid desert and I experience no problems with static build up. Although during the Summer months the temps. climb as high as 115 degrees and between the hot air and wind, the static is hard to deal with. If you could ever come up with a coil cover like you mentioned I would be willing to give it a try. I could almost garantee if it worked I could sell dozens of them to others that are experiencing the same problems during this time. I'm really surprised that a detector company hasn't already thought of the idea???
Talk with you later,
Robert(AZ)

 

[Anonymous]

Rob, You don't know how luck that we are to have someone like Eric listen and respond to our problems. Sadly most metal detector engineers do not use metal detectors at all in the real world. All of their testing is done on a lab brench. I have tested prototypes metal detectors that after I get done testing. I really have to wonder what the engineer were thinking when he designed this prototype. I do have a engineer in one metal detector company that does understand the static problem. But when he talks to the other engineers at this company. They can not understand that it could be a problem. Very seldom we are able to get these engineers out in the real world so that we can show them the problems that we have to deal with. So again be glad that we do have Eric in our corner!
Terry

 

[Anonymous]

I guess another way of puting it would be that the wire has become a "phase cancelling device" in this case(underwater use).
Russ