Walkthrough

[diggerbarns]

Walk through again.

I would like to build a quite simple Walkthrough detector. Running from car battery, so no worry about economy
running. I was thinking about two upright coils about 50 cm apart. Coils being about 30 cm by 120 cm diameter.
About 10 turns .7 wire. Have a few questions.
What sort of pulse frequency should I go for. And would there be any point in the two sample approach rather than

one. Not looking to detect very small items. About pistol or horse shoe size. Coils could be in phase or opposing.

Will have to experiment with this. Many thanks for any advice.I was thinking about 250 khz and 1 sample.

[kt315]

And would there be any point in the two sample approach rather than

one.

sorry for what? you do not need in ground cancel. one sample does work good in your case.

[ripsdevala]

...Than

One.

[diggerbarns]

What about the pulse frequency. Any guidance on that please

[waltr]

That is typically determined by the Integrator RC constants and how long a target would be within the coil's magnetic field.

Lots and lots of discussions in the many threads here.
Search and read, read, read.

[Carl-NC]

What about the pulse frequency. Any guidance on that please

Pretty much anything you want. On a real walk-thru my preference is to run a synchronous multiple of the mains frequency to eliminate mains EMI.

[diggerbarns]

I got this just about worked out now. Two coils about 500mm apart pulsing at 1047 pps. Working quite well over long periods with no falsing. See the result at www.easytreasure.co.uk/walk through.htm there is also a video at https://www.youtube.com/watch?v=R37Mz6EmB-I


Link wont work for some reason but you can work it out.

[diggerbarns]

Link will not work for some reason try www.easytreasure.co.uk/bfo.htm and scroll down

[Carl-NC]

Link works for me. Nicely done! In the US, standard gate width is 30" = 76cm, 50cm seems a bit too narrow. Spreading the coils will reduce sensitivity, but you can make that up a little in a higher pulse rate or other design factors.

[diggerbarns]

Thank you Carl

[Carl-NC]

BTW, I'm heading to a security show in Las Vegas to show off my own WT design, for First Texas. Designing a WT is interesting with its own set of unique challenges.

[diggerbarns]

Hope you have a fruitfull trip