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Beachscan

A

Anonymous

Guest
This is an example of a PI detector that breaks with traditional principles to some degree. Instead of pulsing a high current through a low resistance and low inductance coil it pulses only 0.2A peak through a 10 ohm coil that has an additional 39 ohms in series. The coil also has an inductance of over three times the usual amount but we are still able to sample at the magic 15uS for use on a wet beach. The MosFet can be a small one with a relatively low voltage rating and the mean dc current taken from the batteries is only 65mA giving good life from 8AA cells.
Eric.
 
So Eric, what does this non-traditional PI gain by going to a higher resistance coil and lower current into the coil? Is it better around RF interference or something?
 
Nice picture! Looks waterproof. How does it stack up to the Deep Star and what coil sizes does it come in.
 
Eric when will this unit be available and for what cost? (USA)
 
Hi Charlie
I will be handling them for Eric in the US.
Give me a email, and I will supply you with the information I have.
Bill C.
 
Hi Jeff,
Just an alternative way of doing things really. The low pulse current means that you can switch faster and sample earlier; except in this case the inductance of the coil is much higher so you end up at square one. Noise performance is no better and no worse. The higher pulse frequency results in more samples into the integrator in a given time but the greater number of turns on the coil means more noise to average. The reason for using this technique in the Beachscan is the small 4 pin DIP Mosfet and the small reservoir capacitor. This saves quite a bit of space on a high density board.
Eric.
 
Hi Kurt,
Beachscan is weatherproof but not submersible. The coil is fully waterproof of course and the standard size is 8in diameter. By the way, all the coil sizes that I quote are the actual mean winding diameters and not the overall diameter, as some do. i.e. the 8in Beachscan coil has an overall diameter of 9in.
It doesn't compare to the Deepstar in performance as it runs from 8AA batteries but is similar to the Surfmaster with the mods. for higher sensitivity.
Eric.
 
Hi Charles,
I am sending one to Bill Crabtree this week. I have also just sent him pricing information for the US.
Eric.
 
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