Decagon Devices MAS-1 User Manual - Page 15

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5. Calibration

The current transmitted by the MAS-1 is proportional to the

dielectric permittivity of the medium surrounding the sen-

sor, and therefore its volumetric water content (VWC) of the

medium. The VWC is calculated by applying a calibration

equation to the current transmitted by the MAS-1. The fol-

lowing are generic calibration equations for common growth

media. Applying these equations will generally result in

accuracy of ± 4% VWC as long as the electrical conductiv-

ity of the medium is less than 8 dS/m. If you wish to use the

MAS-1 in a medium that isn't listed below, if you need bet-

ter than ± 4% accuracy, or if you are working in a high salin-

ity material, then you should develop a custom calibration

for your particular medium. See www.decagon.com for

step-by-step instructions on developing a custom calibra-

tion. Decagon can also develop a custom calibration for

your medium; contact Decagon for more details on the cali-

bration service.

Mineral Soils

A single calibration equation will generally result in good

accuracy for all mineral soil types with electrical conductiv-

ity < 8 dS/m. VWC is given by:

VWC = 0.00328 * mA

If your data acquisition system isn't capable of higher order

mathematical operations, the mineral soil calibration can be

MAS-1 Soil Moisture Sensor

- 0.0244 * mA - 0.00565

5. Calibration