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Watermark from Irrometer	AquaProbeTM

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(June 2000) There is a new soil moisture meter recently developed by Mike Hansen of East Wenatchee, Wa. This device is designed to work with watermark sensors from Irrometer Co. This device retails for $379.00. It will accept six watermarks and two soil thermistors. It will both datalog and display a soil moisture graphic for up to five weeks time. It will store up to two years data. The graphic display is activated by pushing a button. There is a web site which is- http://www.mkhansen.com.

See also see Clinton Shock's very good page at http://www.cropinfo.net/granular.htm
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AquaProbe^TM
The key component of the AquaProbe^TM is the sealed membrane sensing element which is connected to the pressure gauge or transducer. A microporous glass tube, coated using a proprietary plasma polymerization process, functions as a reverse osmosis (RO) membrane. Operating range is claimed as 0 to minus 10 bar (145 psi). Suppliers page 1997. from US$69.50 to $239.50 per sensor; Qty discounts. Data Acquisition Software $250.00

Irrometer The Original American Manufacturers. Suppliers index.
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added 2/4/2001

I have heard of individuals getting good results with watermarks and gypsum blocks hooked up as the resistance source in an RC astable multivibrator using a 555 timer.

As the resistance of the block changes, the frequency output of the timer does as well. This way your running a switched DC through the sensor. If you would rather have a voltage output, drop the timers supply current across a low value resistor. The 555 timer is very stable, and with a good quality capacitor in the RC network, should produce good results.

Regards,
Steve Sargent
http://www.slsargent.com/
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