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MAS-1

Calibration

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

tric permittivity of the medium surrounding the sensor, and therefors

the volumetric water content (VWC) of the medium. We can cal-

culate the VWC by applying a calibration equation to the current

transmitted by the MAS-1. The following are generic calibration

equations for common growth media. Applying these equations will

generally result in accuracy of

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

MAS-1 in a medium that is not listed below, if you need better than

6% accuracy, or if you are working in a high salinity 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 calibration. Decagon can also develop a custom calibration

for your medium; contact Decagon for more details on the calibration

service.

5.1

Mineral Soils

A single calibration equation will generally result in good accuracy

for all mineral soil types with electrical conductivity < 8 dS/m. VWC

is given by

V W C = 0.00328 mA

If your data acquisition system is not capable of higher order mathe-

matical operations, the mineral soil calibration can be approximated

by the following linear model. This will result in slightly worse ac-

curacy at low VWC, with errors becoming large above 35% VWC.

5.2

Potting Soil/Peat

The following equation can be used to covert MAS-1 transmitted

current into VWC in potting soil and peat potting mixes. Please note

that diﬀerent potting soil types are quite variable, so this calibration

6% VWC as long as the electrical

V W C = 0.0479

5 CALIBRATION

0.0244 mA

0.00565

0.391

(3)

(4)