More on two-box, CA3035, etc.

[nelson]

Airport Security Metal Detectors

Does any one know what technology is used on Airport Security Metal Detectors.
A friend of mine said that this kind of metal detectors are the same used by two box MD.
If this is rigth, please let me know if is posible to make a two box metal detector from an old Airport Security Metal Detector, because i have some circuits access.
Regards
Nelson

[JC1]

Sure!

Hi Nelson,

Well now it depends on which brand of

walkythrough detector you are talking about.

some have xmit and receiver coils in both sides.

these will not work with side panels.

others which are pulse induction will have

xmit on one side and rec on the other.

So you would have a GIANT two box.

Of course with all of these, little concern

was spent on the design as to power consumption

as they were plugged into the wall.

Even the few portable units the lead acid

battery would be half a car battery.

[Carl-NC]

Does any one know what technology is used on Airport Security Metal Detectors.

Most are PI.

[JC1]

Sounds noisey to me

Hi Chemelec,

Hmmmm,,, you will need some form of

filtering or you should expect alot of

noise. In fact to improve the performance of

many detectors is in the reduction of noise.

Without a doubt there could be phase shift.

Not important if not "trying" to discriminate.

If you are "trying" to discriminate then I would

still recommend some form of filtering to enjoy

the benefits of the performance, and still

perform the demodulation correctly.

One technique might be to Null the coil

slightly in the direction of sending a small

xmit phase signal through and using this

as the reference for the zero and ninety degree

demod, i.e. amplify this signal, square it up

and use for reference.

there might be even better ways than this to

accomplish this.

Certainly the best design would be one which makes

any component drift with temp unimportant in an

area of higher Q, sharp selective filters...

But oh the performance.

like in radios, which are wide enough to

pass the modulation.

only in this case no modulation so can be very

narrow. of the oscillator needs to be somewhat stable

or once again "track" so this error falls out.

[JC1]

Yes, Carl

Hi Carl,

Yes all are PI or Earth Mag now

one is vlf. some of the PI pulse from

one side and then the other which

I guess would still work for two box.

This is really sillly.

[JC1]

Improvement?

Hi Chemelec,

Someone did say improvement

didn't they? oh well maybe not.

Hey filterpro doen't do bandpass filters.

I fired it up and looked. I use other

things which cost money so had forgoten

still could make 2nd order highpass and

then 2nd order lowpass is another option.

and hey if the phase shift bothers you

just open up the passband until you feel

comfortable. Or you can build what has

been built before and if you get it all

right it will perform the way it performed

before.

[chemelec]

Hi Chemelec,

Someone did say improvement

didn't they? oh well maybe not.

Hey filterpro doen't do bandpass filters.

I fired it up and looked. I use other

things which cost money so had forgoten

still could make 2nd order highpass and

then 2nd order lowpass is another option.

and hey if the phase shift bothers you

just open up the passband until you feel

comfortable. Or you can build what has

been built before and if you get it all

right it will perform the way it performed

before.

One object of the 2 box detector system is to have both the recieve and transmit coils Resonant at Exactially the SAME Frequency.
This Tuned Resonant signal Far Outways any Noise.

But with a good power supply and a good Layout, the noise in my circuit is not a problem. But Without a Good Layout, Oscillations Will be a problem.

[nelson]

Twob MD with an airport security MD

HI JC1, and thanks to everyone that reply to me.
Well, i ll call a friend of mine to get the hole circuit and started to study it if i can make a two box with it.
I also don´t know the brand of this MD, but when i get the details i ll share it with you.
Regards
Nelson

Hi Nelson,

Well now it depends on which brand of

walkythrough detector you are talking about.

some have xmit and receiver coils in both sides.

these will not work with side panels.

others which are pulse induction will have

xmit on one side and rec on the other.

So you would have a GIANT two box.

Of course with all of these, little concern

was spent on the design as to power consumption

as they were plugged into the wall.

Even the few portable units the lead acid

battery would be half a car battery.

[nelson]

Two box with PI technology????

Carl.
So if most of airports MD are PI, i can understand that if i make a two box with this technology i ll have a two box pulse induction metal detector...humm... is this ok???... if so, i can figure out, that will not discriminate, but it will go very deep.
Regards
Nelson


HI JC1, and thanks to everyone that reply to me.
Well, i ll call a friend of mine to get the hole circuit and started to study it if i can make a two box with it.
I also don´t know the brand of this MD, but when i get the details i ll share it with you.
Regards
Nelson[/QUOTE]

[Geo]

Carl.
So if most of airports MD are PI, i can understand that if i make a two box with this technology i ll have a two box pulse induction metal detector...humm... is this ok???... if so, i can figure out, that will not discriminate, but it will go very deep.
Regards
Nelson


Nelson

[/quote]

You can build a "2Box type" PI detector BUT Really it will be a PI with 2 coils AND the coils must be parallel between them. But if you want a 2Box detector make a reall 2box. At this forum you will find shematics of white TM808 or GeminiII.Another good solution is to construct the Buccaneer IB detector with 2 coils as 2box. I tried it before years and it worked Very good
Regards

[JC1]

Right

Nelson,

Geo is correct.

[nelson]

Two box MD

Ok, thanks for all the information.
Regards
Nelson