136 Posts in 51 Topics by 53 membersJump to:
|Page: 1||Go to End|
|Author||Topic:how to properly use the calibration equation provided by you for the EC-5||3227 Views|
21 October 2010 at 11:12pm
i have a confusion with calibration equation for the EC-5, because it's not clear for me the way that i should to use it, for example:
you provided this equation: VWC = 10.3 x10-4 * mV - 0.334 for Potting soils, then if with the 2500mV calibration i have an output with ranges between 280mV and 410mV (measurig the output with a multimeter), can resolved like this:
10.3 x10-4 * mV - 0.334
10.3 x10-4 * 280 x10-3 - 0.334= -.3337116
10.3 x10-4 * 334 x10-3 - 0.334= -.3336559
10.3 x10-4 * 410 x10-3 - 0.334= -.3335777
10.3 x10-4 * 1000 x10-3 - 0.334= -.33297 (with 1000mV, that supposed is the maximum output value)
then i wonder, which ones are the values of VWC really?. unless the way to write the formula is: 10.3 x10-4 * (mV - 0.334) then can resolved like this:
10.3 x10-4 * (mV - 0.334)
10.3 x10-4 * (280 x10-3 - 0.334)= -.05562 x10-3
10.3 x10-4 * (334 x10-3 - 0.334)= 0
10.3 x10-4 * (410 x10-3 - 0.334)= .07828 x10-3
10.3 x10-4 * (1000 x10-3 - 0.334)= .68598 x10-3
but, what are these results? if every value lower than 334mV are negative, and it's supposed that the values are in m3(cubic meters), how i should interpret these results?
unless the ways of how it has resolved the formula are wrong, and if that is the case, would appreciate that explain me how i should interpret the formula (with brackets to facilitate understand it) and how interpret the results too.
thanks for your attention.
22 October 2010 at 9:56am
You should get 10.3*10-4 (or 0.00103) *mV - 0.334
So for 280 mV your m3/m3 = (0.00103*280) - 0.334 = -0.046 m3/m3
and (0.00103*410) - 0.334 = 0.088 m3/m3
Is your sensor buried all the way up to the cable? Keep in mind that there is measurement sensitivity in the black plastic part of the sensor, so if you have just the prongs buried you will also be reading the moisture content of the air and your soil volumetric water content will be underestimated.
22 October 2010 at 11:54am
Hello Virgil, thanks for answer
yes, just the prongs are buried, so i have a wrong measure, right?. ok, i'll test burying completely the sensor, thanks.
but i have a doubt, if i still get negative values with the formula, what means?
25 October 2010 at 2:38pm
Yes, if just the prongs are inserted you are underestimating VWC. I think you will not see negative numbers once you have the probe inserted all the way unless you have a large amount of organic matter in your soils or if your soils are oven dry (by definition 0, +/- 1-2%).
Please refer to a previous post on this topic for more details (http://www.decagon.com/forums/soil-moisture/show/6#post6).
|Go to Top|
Currently Online: There is nobody online.
Welcome to our latest member: jrslover