On Fri, 30 Aug 2002, Brendan Moran wrote:

>> That's why you do not use the earth field, instead you swamp it using a
>> strong field of your own from a pm, besides the magnetisation/readout
>> coil. This causes the precession frequency to be higher than usual for
>> these instruments.
>
>Yeah, I know.  In fact, the post that followed gave a full description of
>how to implement this.
>
>> Why would anyone try to use this expensive and complex method to detect
>> water I don't know.
>
>Frankly, as this list has many hobbyists on it, why not?  It's not as
>complex as all that... A magnet, two coils, an oscillator, a power amp, a
>preamp, an opamp integrator, and a micro...

Run some numbers, will you. Esp. wrt the amplitude of the output signal
(as in output signal, in normal house/industrial environment ...). You
will need a LOT of protons to have a decent signal even with a very good
preamp.

The only advantage of the constant pm field is, you can use a narrow band
preamp, unlike in magnetometers. This helps with s/n.

>process is: send; receive; measure; reset
>
>I doubt that this is too much more complex than either sonic coupling or
>microwave absorbtion...

All the principles are simple, the devil is in the details.

Thermal conductivity is a well known method for doing this. National even
had (has?) a chip to interface with the wire thermistor kind of gauge
(the kind often used in fuel tanks). I DIYd such a circuit a long time ago
and it worked ok but was not linear. I used a 20 ohm piece of wire (2
meters of 10R/meter).

Peter

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads