Campbell TDR100 Instrukcja Obsługi Pobierz pdf (Strona 29)

TDR100

6.2.12 Parameter 12: Multiplier

Multiplication factor applied to the value stored in the input location specified

in parameter 11. Set to 1 when parameter 2 is 1 or 2. The multiplier can be

used for the probe constant value when measuring electrical conductivity.

6.2.13 Parameter 13: Offset

Offset value added to the value stored in input location specified in parameter

11. Set to 0 when parameter 2 is 1 or 2.

6.2.13.1 Probe Constant for Electrical Conductivity Measurement

The section, TDR Principles, presents the equation used for soil bulk electrical

conductivity. For convenience, it is repeated here.

−

A portion of the datalogger algorithm evaluates the reflected waveform to

determine the applied and reflected voltages. From this, the reflection

coefficient, ρ, can be calculated. The term, Z

, is the reflectometer impedance

and is a constant 50 ohms.

The electrical conductivity routine in the datalogger returns the value

−

which must be multiplied by the probe constant, K

, to get an electrical

conductivity value.

The probe constant (K

) is easily determined using PCTDR or can be

determined through calibration. The probe rods are immersed in solutions of

known electrical conductivity and values of

−

collected by the

datalogger. A linear regression of known electrical conductivity to the result

from the datalogger will have a slope equal to the probe constant. When

performing a calibration with independently measured electrical conductivity,

take caution to account for the strong temperature dependence of electrical

conductivity. This calibration is generally recommended if accurate absolute

electrical conductivity values are required.

Laboratory calibrations were performed to determine a K

value for the

CS600, CS605 and CS610 probes with the following results.

TABLE 6-2. Probe Constant Values for Campbell Scientific Probes

Probe model probe constant (K

)

CS600 3.16

CS605 & CS610 1.74

1 2 ... 24 25 26 27 28 29 30 31 32 33 34 ... 55 56

Brak uwag

Campbell TDR100 Instrukcja Obsługi Strona 29