DELTA PULSE / SNIFFER XR71 PULSE INDUCTION METAL DETECTOR

Hello everybody.
Since I work on the EMI/RFI problem, I start to discover som realities.
Experts from this forum can correct my summary to avoid broadcasting
wrong informations.

It is impossible to shield a coil against low frequencies magnetic fields
like them from power lines (50/60Hz)
I didn't try the graphite spray shielding for reducing ground effect.
It should be useless for detecting big iron objects with a frame coil.
I should can operate with a very long delay before sampling so the
ground signal would decay much faster than a big iron object.
I think about lowering the coil resistor value from actual 6 ohms
to 3ohms (I need to adjust coil turns and wire section to observe a
good tuning).
The decay time to 0v should still be faster than a long sampling delay.
I could tune the damping resistor value to adjust.
The idea is improving strength of magnetic field emitted by the coil
to receive à stronger field from the object. So I could reduce sensitivity
behind the chattering level from power lines and keep a good detecting
ability for big iron objects.
What about the theory? Thank you.

Ps: still hard to undertand the tuning from each potentiometer on the delta pulse.
can somebody confirm or join a link?
Noise= pulse width?
Signal= delay?
Sens?
Gain?
 







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Hi. it's the Delta Pulse 2 from the download section

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I dont like asking the same question.
Please accept it's not my first language. I was misunderstanding EMFI and ESFI acronyms.
Technical langage is far way more difficult to understand than: "Where is Brian? Brian is in the kitchen"
Thank you for understanding. Merci pour votre compréhension.

Do you know why Eric Fosters says:

"The important thing was to avoid the same frequency as power lines, 50Hz in the UK, 60Hz in the US. Multiples of the power frequencies also had to be avoided e.g. 100 or 120. Severe beat note interference would result if the detector and power frequencies coincided; that is if you were anywhere near power lines as is often the case in the UK."





Posted on: May 17, 2018, 12:44:11 pm

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"blackout the power line in your seeking places"
LOL. I thought about it but the line is coming from a nuclear power plant


Posted on: May 17, 2018, 02:01:25 pm

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As you say, tuning frequency on 100Hz (or even 50Hz I think) should be efficient. Lets imagine a power line emitting 50Hz magnetic field and delta pulse tuned to 50 Hz frequency.
If the delta pulse is sampling the signal while the power line magnetic field is at the bottom of the wave, it should't be any interference.

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Mudflap is right, as is Eric Foster. Something is being lost in translation to what NE555 is saying. Stay the hell away from the resonant frequencies and you will be fine. The main priority is to do your testing and setup in an interference free environment, so as not to be distracted or confused by the resulting performance changes.
When you go out in the field where there is interference, you will then be very aware something is wrong and may need to be remedied.

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Thank you guys, it's nice from you sharring your knowledge
I think everybody is right and meaby there are two ways to work against EMFI.
As you say Mudflap, for tuning on 100Hz without drifting it requires a very hight quality and stability circuit.
The most important to progress is understanding.

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