Emi problem

[Daves]

Hello everyone,
How can I solve the EMI problem of a metal detector?
I operate the metal detector in a room, above the ground, without any metal objects under, next to, or around it, and it constantly receives signals, never stops, and displays ID. Does anyone have any analog or digital suggestions on this subject? What are the EMI sources and if you have any different suggestions in general, I would like to learn about them.

Note: Sometimes it can be quieter in the same place. Sometimes it can be always quiet, but there is generally noise there.

[Carl-NC]

1. Try turning things off to find out what makes a difference. Everything is suspect: fluorescent lights, LED lights, WiFi, your cell phone, the refrigerator, etc etc.
2. Try rotating the coil is different orientations to see if it gets better/worse. Sometimes this will help identify where the EMI is coming from.
3. Build an EMI-canceling coil.

[Daves]

1. Try turning things off to find out what makes a difference. Everything is suspect: fluorescent lights, LED lights, WiFi, your cell phone, the refrigerator, etc etc.
2. Try rotating the coil is different orientations to see if it gets better/worse. Sometimes this will help identify where the EMI is coming from.
3. Build an EMI-canceling coil.

Carl, thank you for your suggestions.
The solution I am looking for is more about the precautions to be taken when producing the detector.

1. What is an Emi cancelling coil?
2. Should I use a software filter for Emi? I have no idea what kind of filter is used.
3. Should I take a different precaution in coil production?
4. Does the coil rx, tx wire thickness affect this?
5. Does the graphite shield value in the coil affect this? How many kohms should I measure when I measure an average of 1cmx1cm?

[Carl-NC]

Ok, it sounded like just an indoor problem. First, get the detector out of the house and see how it is. Indoors is a terrible environment.

1. An EMI-canceling coil includes Figure-8, Tophat, coaxial, and a few others. Do a forum search, they have been discussed.
2. Also hardware filtering. Depends on whether it's VLF, PI, or MF.
3. I don't know.
4. Not enough to worry about it.
5. Yes, the lower resistance the more E-field attenuation. But this also increases shield eddy losses. Build a few coils with different coats of shield paint, see what works.

[pito]

What is showing oscilloscope connected to output Rx amplifier ? Check shielding by spraying some water on coil.

[Riss]

Years ago, after repairing a very cheap Chinese VLF , a customer told me that music and speech could be heard from the speaker – from a nearby medium wave transmitter. I told him to give me a bottle of wine – for the extra upgrade

[Daves]

What is showing oscilloscope connected to output Rx amplifier ? Check shielding by spraying some water on coil.

If it beeps when I spraying water, do I need to increase the graphite shield value? What should I do and what should the values be?

[pito]

show picture of the coil, you have shielding problem.

[Daves]

show picture of the coil, you have shielding problem.

what do you suggest?

[Carl-NC]

Have you taken the detector outside, away from the house, to see if it's still noisy?

[Daves]

Have you taken the detector outside, away from the house, to see if it's still noisy?

Yes, I turned on and used the metal detector in places such as fields, beaches, indoors, mountainous terrain. The interference I mentioned only occurred in the city and at home. In addition, when I went to the beach last time, I used the detector for about 6 hours. There were continuous interferences that came every 2-3 times. At that time, boats and ships were passing around me, I was not sure if it was because of that or not. The interference went away on its own afterwards.

I produced the coil I used in the detector more than once. I wonder if I did something wrong when producing the last coil, i dont know

[Carl-NC]

So is the EMI problem specific to one particular coil, and other coils are OK? Does this have anything to do with your cable question? It's important to provide all relevant information up front.

[Daves]

So is the EMI problem specific to one particular coil, and other coils are OK? Does this have anything to do with your cable question? It's important to provide all relevant information up front.

same detector, same feature coil =
*When you touch the side of the cable that enters the coil, there is always a problem of target id coming.
*There is always interference inside the house.
*I produced the same coil with the cable of a different detector. When you touch the cable, target id does not come, the coil is stable but there is still interference inside the house.
*I went to fields, mountainous areas with coils with problematic cables, if you do not touch the cable and there is no problem. Emi did not come from the environment. The last time I experienced the Emi problem was on the beach and it went away by itself but there is always Emi inside the house no matter what the cable is.

[Teleno]

If yur cable is using the return signal as a shield (single core coaxial), which I saw for example in a mono Commander coil, then anything induced in the shield gets added to the signal. I'm going to replace the cable with a two core coaxial so the shield and the return signal are connected to ground separately and see if it's less noisy.

[Carl-NC]

same detector, same feature coil =
*When you touch the side of the cable that enters the coil, there is always a problem of target id coming.
*There is always interference inside the house.
*I produced the same coil with the cable of a different detector. When you touch the cable, target id does not come, the coil is stable but there is still interference inside the house.
*I went to fields, mountainous areas with coils with problematic cables, if you do not touch the cable and there is no problem. Emi did not come from the environment. The last time I experienced the Emi problem was on the beach and it went away by itself but there is always Emi inside the house no matter what the cable is.

EMI inside the house is normal. Next thing you need to show is what cable you used, exactly how it is connected, and how you shielded the coil.