How does a manufacturer test a detector?

[Koala]

This guy seems to have one as bad as mine and thinks it’s ok: https://m.youtube.com/watch?v=sWKM39s82nY#dialog

This guy’s seems to work better: https://youtu.be/RfAOJTAAV4w

threshold is way too High on first video. Any small signal is swamped. He is correct about the steady threshold though

[dbanner]

Good idea.

I believe they are wired in series so if one fails they both fail.

So I thought, until I had another look at the whites dual field patent again, the damping resistance across both coils, even if outer coil is open, inner coil may still work albeit with diminished sensitivity. That's why I suggested putting tiny object on edge of outer coil just to make sure it's responsive.
Or maybe not. Just something to try.
On second thought, if the inner coil becomes open, the outer coil will still work via the inner coil damping resistor, but the overall damping will be wrong, resulting in reduced sensitivity. So check to make sure inner coil is responsive with tiny bit of foil.

[dbanner]

Also if the inner coil has become open, a resistance meter will measure on the order of several tens of ohms, even as high as 100 ohms.
I think
This is sure indication coil is bad
Of course, trying another self made mono coil will reveal everything.

[bklein]

245uH coil
both coils sense target

[Koala]

running out of ideas everything appears okay.

Is it the same on headphones ?

[dbanner]

Go the Spock route. Eliminate all the possibilities, whatever remains, regardless of how improbable, must be the answer. The front end preamp chip might be China special. Have a good look at the chip. Look for stripe across the top. Probe output of preamp on scope if you can.
No way a surf dual field can only detect man ring at 5 inches. Russian pirate pi can do that.
I wonder how it got past QC testing at the factory.

[dbanner]

Just out of curiosity, is there a damping resistor on the circuit board or in the chassis box? I suspect not. I would expect them to be in the search coil assembly.( According to the patent)

[dbanner]

This guy seems to have one as bad as mine and thinks it’s ok: https://m.youtube.com/watch?v=sWKM39s82nY#dialog

This guy’s seems to work better: https://youtu.be/RfAOJTAAV4w

The first video is of crazy man. That detector is rubbish.

[bklein]

I finished installing the cable on the original coil. Both it and new one same inductance.
There “may” have been some resistance in the coil connection (2 pin header connect) to the pcb as when I first looked at it it was working very badly like only seeing close iron. Moved things around and it seems back to its normal. So much EMI in my bench it is hard to do comparisons plus it was getting to 2am... I’m thinking the original coil is a bit better but won’t know until later today when I take it all to an open park area. I want to try my homebuilt mono coil too.
The damping resistor is soldered at the coil pcb junction (under side) and is 845 ohms.
I am having a hard time finding much discussion about the differential integrator circuit used on pi’s. Why isn’t the different pulse width of the two samples an issue? What are the design parameters of concern here? What difference does it make to change the sample period and spacing?

[Qiaozhi]

I finished installing the cable on the original coil. Both it and new one same inductance.
There “may” have been some resistance in the coil connection (2 pin header connect) to the pcb as when I first looked at it it was working very badly like only seeing close iron. Moved things around and it seems back to its normal. So much EMI in my bench it is hard to do comparisons plus it was getting to 2am... I’m thinking the original coil is a bit better but won’t know until later today when I take it all to an open park area. I want to try my homebuilt mono coil too.
The damping resistor is soldered at the coil pcb junction (under side) and is 845 ohms.
I am having a hard time finding much discussion about the differential integrator circuit used on pi’s. Why isn’t the different pulse width of the two samples an issue? What are the design parameters of concern here? What difference does it make to change the sample period and spacing?

The main sample and earth field pulse widths should be the same.

[Carl-NC]

The main sample and earth field pulse widths should be the same.

Yeah I don't understand this either, though it wouldn't affect target sensitivity.

[green]

The main sample and earth field pulse widths should be the same.

Don't have a schematic so don't know if capacitor coupled before the integrator. Have wondered if earth field pulse might need to be longer if capacitor coupled?

[bklein]

Tried original and new coil at a low EMI park and both are pretty much identical and sense all coins at the 7-8” range.
Comes down to my original question. I would expect there to be a setup to replace the coil to test the circuitry - something you tweak and check the response with.
I guess it is time to go into Spock mode.

[Koala]

If you turn the gain control down does the distance reduce ?

[dbanner]

Nobody ever considers the efficacy of the chips soldered on the board. There are some bad performing opamps that are never suspected. Also I would put variable damping circuit just to see what effect it has on performance, slightly over damped or under damped can improve sensitivity.
The pulse width of both samples should be the same in this rather simple circuit.