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Offline Super Pierrot
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« Reply #810 on: May 12, 2018, 06:41:11 am »
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Dear NE555

Thank you for adding Eric Foster's explanation.

He says: The important thing was to avoid the same frequency as power lines, 50Hz in the UK, 60Hz in the US
So I understand: NO 50Hz

He says: Multiples of the power frequencies also had to be avoided e.g. 100 or 120
So I understand: NO 100Hz NO 120Hz

But I also understand NO MULTIPLES OF POWER LINE FREQUENCIES
So: NO 100 150 200 250 300 350 400 450 500 550 600.....
   
                         
You say: you take 100 HZ AND MULTIPLY IT ON EVEN NUMBER.
So I understand: OK FOR 200Hz 400Hz 600Hz......

Nothing against anybody but it seems to be a contradiction.
Or meaby I didn't understand anything.. Sad












Posted on: May 12, 2018, 06:31:10 am
Dear Homfire.
You said: Yes it would be better to keep your pulse rate away from the 50Hz and or Harmonics of the same.  100, 150 or 200Hz  ...
I understand : NO 50 100 150 200Hz...
Do I understand correctly? (The word "Harmonics" can cause misunderstanding for me. Did you mean "multiple"?)



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Offline NE555
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« Reply #811 on: May 12, 2018, 06:55:31 am »
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my mistake. you take 50 HZ AND MULTIPLY IT ON EVEN NUMBER.

Posted on: May 12, 2018, 06:45:27 am
OPEN THIS LINK AND READ

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In physics, interference is a phenomenon in which two waves superpose to form a resultant wave of greater, lower, or the same amplitude. Interference usually refers to the interaction of waves that are correlated or coherent with each other, either because they come from the same source or because they have the same or nearly the same frequency. Interference effects can be observed with all types of waves, for example, light, radio, acoustic, surface water waves or matter waves.

Posted on: May 12, 2018, 06:49:46 am


Quote:Posted by Super Pierrot

I can see famous pulse induction detectors with ajustable  frequency in order to tune when near power  lines. Whites tdi and lorenz lpx2 for example.


adjustable  frequency is only a battle with interference. but it may by NOT only 50Hz. you have mobile, wi fi, tv set lines etc and all those
are huge EMI field around you.


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« Last Edit: May 12, 2018, 06:56:48 am by NE555 »
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« Reply #812 on: May 12, 2018, 07:14:39 am »
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   Yes Harmonics are multiples of the fundamental frequency.   Sub Harmonics can also come to play.  As NE555 says Power lines are not the only RFI Issue.  There are thousands of RFI sources that can mess with you.  

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http://www.youtube.com/watch?v=um0Shx9DWSI


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« Last Edit: May 12, 2018, 07:47:13 am by Homefire »
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« Reply #813 on: May 12, 2018, 11:13:55 am »
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Thank you guys for your answers. I think I understand better the problem of EMI.
More than calibrating on an accurate frequency, I should avoid some frequencies(and their multiples)
that could superpose with the ones produced by power lines, mobile, wifi ....
In practice, I tuned the Delta Pulse frequency from 85 to 400Hz(IRF 740 starting to overheat), and I never found
It could be more stable. I tuned sensitivity just above the stability level to make sure to not
overload and to feel any improvement.
Do somebody have any other ideas to improve protection against EMI?



Posted on: May 12, 2018, 11:07:01 am
I forgot to say that I already use an 8 shape coil and I can say it's very effective against EMI but for
very (very very Cool) big frame, the Delta Pulse start chattering near (500meters) big power lines.

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« Reply #814 on: May 12, 2018, 03:25:45 pm »
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  Your only other option is to RFI shield the Coil and Control Box.

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« Reply #815 on: May 13, 2018, 12:20:19 am »
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you use very high sensitive detector with big antenna. big antenna mean big receiver signal. use less poor sens detector.
like fisher 1210, bounty hunter, tesoro etc. with coil 6-8 inch. i released GMT King Cobra (tesoro royal sabre). my projects cover all areas of use.


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« Last Edit: May 13, 2018, 12:21:47 am by NE555 »
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« Reply #816 on: May 13, 2018, 05:47:37 am »
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I understand it's a very sensitive detector with a big antenna. Improving performances against RFI/EMI with such a big coil is a challenge.
I think a smaller coil with 8 shape would work much better in the same place. I made Ó 2.8x1,4m that works very well near power lines,
but it's a medium size comparing.
Shielding method is interesting. I try understanding how it works and if it can be applied to big frames before asking questions.  Wink




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« Reply #817 on: May 13, 2018, 09:34:15 am »
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you can use only ESFI shielding, not EMFI protection. EMFI protection is also ESFI one, but not contra.
if you will use copper foil you much lose the sensitivity. you can use foil in VLF coil but it is also lose of sens.

ESFI elecrostatic field influence. graphite layer connected to ground of your schematic.

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« Last Edit: May 13, 2018, 09:36:25 am by NE555 »
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« Reply #818 on: May 13, 2018, 11:09:21 am »
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Sorry but I don't understand (didn't find on the net) EMFI and ESFI signification. I understand I should use a graphite layer(I was thinking about trying this way).
The frame is made from PVC tubes and the coil cable is inside. So I just can use a graphite spray to shield on the tubes.
I have no idea of how the magnetic field from the coil can travel through the graphite shield and come back from the mettalic object
from the sam way while EMI and RFI would be reduced.

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« Reply #819 on: May 13, 2018, 02:34:27 pm »
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   Yes Graphite or Copper Shield would help.  I just use copper tape on most PI coils.  Works for me. 

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