watermark sensor adapter

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black_unicorn
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watermark sensor adapter

Postby black_unicorn » Tue Nov 04, 2014 8:12 am

For use in agriculture.
It would be interesting to have an adapter compatible with Phidgets, able to make a WATERMARK sensor readings.

In use since 1978, the patented WATERMARK sensor is a solid-state electrical resistance sensing device that is used to measure soil water tension. As the tension changes with water content the resistance changes as well.

The sensor consists of a pair of highly corrosion resistant electrodes that are imbedded within a granular matrix. The adapter must correlates the resistance to centibars (cb) or kilopascals (kPa) of soil water tension.

Currently there is this:
WATERMARK 200SS-VA (Voltage Adapter),

http://www.irrometer.com/pdf/sensors/40 ... VA-WEB.pdf
http://www.irrometer.com/pdf/supportmat ... -chart.pdf

Is it compatible? If yes.
What should be the physical connection and logic implementation?

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mparadis
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Re: watermark sensor adapter

Postby mparadis » Tue Nov 04, 2014 8:39 am

Yes, that sensor is compatible with Phidgets. To implement it, you could take a Phidget sensor cable and cut off one end, then solder the red wire to the WATERMARK's red wire, the black wire to the WATERMARK's black wire, and the white wire to the white wire.

In software, you can convert from SensorValue using the equation in the PDF you attached:

Pressure (kPa) = Voltage (V) / 0.0117155 = (SensorValue/200) / 0.0117155

Simplifying,

Pressure (kPa) = SensorValue/2.3431

black_unicorn
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Re: watermark sensor adapter

Postby black_unicorn » Tue Nov 04, 2014 8:42 am

mparadis wrote:Yes, that sensor is compatible with Phidgets. To implement it, you could take a Phidget sensor cable and cut off one end, then solder the red wire to the WATERMARK's red wire, the black wire to the WATERMARK's black wire, and the white wire to the white wire.

In software, you can convert from SensorValue using the equation in the PDF you attached:

Pressure (kPa) = Voltage (V) / 0.0117155 = (SensorValue/200) / 0.0117155

Simplifying,

Pressure (kPa) = SensorValue/2.3431


mparadis, Thanks!

black_unicorn
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Re: watermark sensor adapter

Postby black_unicorn » Tue Nov 04, 2014 8:48 am

black_unicorn wrote:
mparadis wrote:Yes, that sensor is compatible with Phidgets. To implement it, you could take a Phidget sensor cable and cut off one end, then solder the red wire to the WATERMARK's red wire, the black wire to the WATERMARK's black wire, and the white wire to the white wire.

In software, you can convert from SensorValue using the equation in the PDF you attached:

Pressure (kPa) = Voltage (V) / 0.0117155 = (SensorValue/200) / 0.0117155

Simplifying,

Pressure (kPa) = SensorValue/2.3431


mparadis, Thanks!


mparadis, one simple question.
Why SensorValue/200 is equals to Voltage (V)?

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mparadis
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Re: watermark sensor adapter

Postby mparadis » Tue Nov 04, 2014 9:51 am

SensorValue (the number you get in software) ranges from 0-1000, and Phidget analog input ports read voltage values from 0-5V. Thus, the linear relationship between the two is Votage = SensorValue/200.

black_unicorn
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Re: watermark sensor adapter

Postby black_unicorn » Tue Nov 04, 2014 10:02 am

mparadis wrote:SensorValue (the number you get in software) ranges from 0-1000, and Phidget analog input ports read voltage values from 0-5V. Thus, the linear relationship between the two is Votage = SensorValue/200.


Is true! 1000/5V, (like a newbie question) :oops:


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