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Metal detector is triggered falsely by the motors nearby

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AceOfHearts

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Hi there...

Basically, I have the search coil mounted in front of my chassis which has 4 DC motors on it.

The vehicle is to scan an area and transmit the information to a remote unit. The unexpected problem I have encountered is that when the motors are on, the metal detecter is being falsely triggered.

I assume it is something to do with electromagnetic (EM) waves generated from within the motors which is triggering the metal detector as it works on the principle of detecting varying EM strengths. I was wondering if anyone know of any material I could get hold of which I can cover the motors with so that external EM waves are kept to a minimum?

As always, I appreciate any help!

Thanks very much for reading. :)
 
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oooooooooh the same problem..
i have seen that un expected problem in my robots too..
there are 2 ways to over come and i have tried both of them and get good job


(1) if u dont care about waight

you can cover all the motors by ONE thin sheet of metal and connect it by graund (earthed) ..
but u have to put that sheet between the sensor and the motors ,i mean that if the sensor is on higher level so u may put the sheet above the motors.. got me??

(2)

u may leave the motors and try to case the sensor by some thing like metal cup so the metal will serround the sensor form every where exept the sensing nop .. also connet the cup by graund..

good luck my friend
 
EMF shielding........

Thanks very much for your suggestions! Do you think using alluminium kitchen foil will work?

I had a similar problem with a PIC being triggered by nearby switching power supply's and shielding with copper or aluminum foil did not help. It wasn't until I wrapped the PIC and its circuitry in metal, from food can, that was steel, that the problem was solved.

Only partial shielding was required, here is a picture:

Professional Model. photo - Rolf photos at pbase.com
 
i used a thin sheet about 0.9 mm steel and it was effecint..
remmark: the motors are the main source of noise in ur system.
 
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about the foil the main problem is that can u connet it by ground and be sure that u have overcome the isolating film which on ot to prevent the food from direct contact with the metal
 
While mumetal would be ideal for magnetic noise, it is was more thaqn a bit pricy last I looked into it, which was admittedly over 15 years ago.

Dan
 
Hi Friends,

When DC brush type motors run they create a lot of electrical noise. If the search loop is tuned for a frequency that is interfered by that noise you will get false results. Bypassing the brushes at the motor and isolating the detector circuitry power supply from the motor power supply may help.

Joe
 
Have you tried wrapping the PC board in packing foil? Aluminum foil as a shield would require frequent replacement, aluminum or light steel sheeting would be best if only the ground wire(s) are attached to it.
 
You DID put a rfi filter right on the motor itself, didn't you? Cap across the terminals, cap to ground each side, couple little inductors in series with each lead...?
 
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