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I agree with Bklein. Post 471 the scope shot looks to be over damped. The clipped part of the flyback is almost 15us at 4us/div. I'm guessing the first sample is pegged to one of the rails. So only the second sample is being indicated. Which might explain the reverse signals on metal and ground noise. You might try a 470 ohm damping resistor or check the input diodes for damage.
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1. Doubt the ground is that bad. None of the rest of my detectors are putting up a fuss.
2. Dry dirt... I live on the Oregon, USA coast. It's been raining for 30+ days. ;-)
3. I can dance, with passion, with the ANPI in the air. No false signals.
Over damped... Maybe? Scope readouts attached. Tested against both my know good basket coil and the GPX Mono coil. GPX_Mono2 has the 350 ohm. I think that's the sweet spot for this coil.Comment
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GPX wiring diagram
Here?s a diagram I suspect is correct for the coil wiring. I referred to this for my GP Extreme.
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That sounded like the best explanation so far until I looked at ding's latest scope plots. The GPX coil looks every bit as fast as the basket coil.Originally posted by Altra View PostComment
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Yes, the second set of photos look normal.Comment
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Does either coil false signal when your hand is placed near the coil?
Which damping resistor are you using, first, second or third picture?
What first delay time are you using?
Do both coils have a similar decay picture with a quarter placed on the coil center?Comment
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Can you post an image/drawing of your connections to the coil socket?Comment
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The Detech site says this (I wonder if it is causing trouble? What do they have in the coil for this?):
Detech is the first to build coils with magnetic sensors, enabling pulse induction detectors to discriminate between ferrous and non-ferrous metals.
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I believe I am following the coil pin out correctly. Thanks for posting that @bklein.
No false signal when my hand is near, on, or sweeping over the coil(s).
Photos attached. My home brew socket adapter has a 350ohm damping resistor. I think the perfect value for the GPX is 340~350ohms, based on what I am seeing from my oscope.
In the field I have been using a simple elliptical coil. It works rather well. I need to try my basket out to see if it's getting the same failure mode as the GPX. I will strive to pull that off tomorrow. A bit tricky with a newborn in the house.Comment
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Would the GPX coil work if the delay times were the same for both coils?Comment
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The socket adapter picture appears to show a cold solder joint at the top of your resistor connection.Originally posted by dingbatca View PostComment
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Thanks for posting the socket adapter photo, but I cannot see how it's wired up, even if I zoom in. A simple hand-drawn diagram may be better.Originally posted by dingbatca View PostComment
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Thanks for the photos. The GPX coil no target trace appears to take twice the time to flatten as the basket no target coil trace. What could cause the slower decay?Originally posted by dingbatca View PostComment
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Very strange...
Two questions:- Can you probe the coil plug with a multimeter and find which pins the mono loop is connected to? I would presume it will be pins 4 and 5.
- If this is the case, then try connecting the ANPI to only those pins. i.e. leave pins 1, 2, and 3 disconnected. What is the result?
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