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Thanks Gunnar, Yes I can detect the tattle tapes OK, but my problem relates to the detection of whether there is onl;y one strip or multiple strips in the same area and at close proximity? Any ideas ? I was thinking of somehow detecting the interference pattern from multiple strips but since...

DspDad - many thanks for the useful advise. I tried a preliminary setup today and it works as you say, but I now need to work on getting a higher Q value by playing around with coil design. One problem is I need fairly large values of Capacitance to store sufficient energy and this means lower...

Brian, Coil inductance is 0.25H, Wire Resistance is 20 ohm, operating from 240Vac 50Hz supply. In magnetizing mode I need approx 15A DC @ 300VDC to get the required field strength which is the maximum the circuit will allow due to wire resistance. In Demagnetizing mode the inductance presents an...

Hi Can anyone sugguest a suitable method for the design of a suitable circuit for a demagnetizer coil. I currently use a HV 470mfd @ 300V Capacitor that is discharged via an SCR into a coil for magnetizing function which works fine but I also need a demagnetizing function? Normally I would use...

The magnetizing & de-magnetizing aspects are relatively straight-forward using standard techniques as I have tested this to some extent, but a "reliable" method for detecting the presence of the strips (in their demagnetized state) is a problem? I want to be able to detect the strips...

To make a detector offcourse and go into competition with 3m! ... and maybe also to satisfy our curiosity???

Melone, No technical info from 3m (a standard 3m practice) - they want you to buy their machines at enormous costs which is fair enough. The technology has been around for some 40 years or so but I can find no info! I dont want their machines but their tattle tapes are cheap and can be applied...

Hi, Does anyone have any info on Tattle tape security Strips and how they can be magnetized and demagnetized and in particular how one can "sense" whether one and more than one strip is placed within a specfic area? The 3M tattle strips seem to have 5 sections which are magnetised -...

Hi, How do tattle tape detection systems work? I need to be able to detect whether one and if more than one tapes/stips are within a small working area ? - any idea's. The stips are about 140mm long and broken up into 5 sperate sections and are magnetised to de-activate them and - demagnetized...