SM150T User Manual 1.0
Appendix 2:
52
Voltage Excited
You need to know the excitation voltage (Vref), reference resistance (Rref).
The correct resistance is given by the equation:
R = a0 + a1 * Rmeas
Where:
a0 =
– Ic.Rc.Rref / Vref
a1 = 1
– Ic.Rc / Vref
Ic = 18 mA (SM150T sensor supply current)
For Delta-T
EXT/5W-xx
series cables:
Rc = 0.066 Ω.m-1
For the
SMSC/lw-05
5m logger cable
Rc = 0.33 Ω
Current Excited
You need to know the excitation current (Iex).
The corrected resistance is given by the equation (using terms defined above):
R = Rmeas
– Ic.Rc/Iex
Effect of Temperature on Water Permittivity
See
Temperature response of soil moisture readings
on page 35
