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slippedangel (Electrical) (OP)
25 Jul 02 6:56
Hi,

I am currently using the philips 8051 to detect a magnet passing an AMR sensor. Does anyone have any ideas or recommended reading to get near 100% detection and near 0% false activation from noise.

In the perfect situation the digitized signal is a single sin-wave pulse with polarity depending on the magnet orientation. In reality this get distorted by magnet speed/offset/angle/etc

The 8051 is 22Mhz with 1kB RAM so I can't really do any complex spectral analysis.

Any suggestion would be wonderful.

Gabriel
cbarn24050 (Industrial)
25 Jul 02 9:34
Hi, I'm not sure what you mean by "digitised signal" in this application.If you have allready used analouge to digital conversion then all you need to do is trigger the 8051 from 1 of the higher data bits. If you are using the analouge signal directly then you can use a schmit trigger to remove the noise.
IRstuff (Aerospace)
25 Jul 02 10:10
There is no magic circuitry involved.  It's strictly a matter of signal to noise ratio (SNR).  You don't stipulate what near 100% means, but a 99% probability of detection with a 1% false alarm rate requires around 7:1 SNR.  

This can only come from a stronger signal, which means a stronger or closer magnet or a lower noise detector, which means possibly a more sensitive detector with integrated low-noise preamp located director at the detector.  

TTFN
nbucska (Electrical)
25 Jul 02 12:55
You can reduce the noise by
1.) shielding 2.) filtering 3.) amplitude and duration
windowing

<nbucska@pcperipherals.com>

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