Campbell CS616 Manuel d'instructions télécharger pdf (Page 42)

CS616 and CS625 Water Content Reflectometers

Method D4643-93 requires heating in microwave for 3 minutes, cooling in

desiccator then weighing and repeating this process until weigh is constant.

Gravimetric water content is calculated after the container weight is accounted

for.

wet dry

dry

m m

−

For the bulk density

bulk

dry

cylinder

volume

the dry weigh of the sample is divided by the sample tube volume.

The volumetric water content is the product of the gravimetric water content

and the bulk density

θ θ ρ

v g bulk

= *

The average water content for the replicates and the recorded CS616/CS625

period are one datum pair to be used for the calibration curve fit.

8.4 Collecting Field Data for Calibration

Required equipment

1. CS616/CS625 connected to datalogger programmed to measure probe

output period

2. Cylindrical sampling devices to determine sample volume for bulk density,

e.g. copper tubing of diameter ≥ 1” and length about 2”

3. Containers and scale to measure soil sample weight

4. Oven to dry samples (microwave oven can also be used)

Data needed for CS616/CS625 calibration are the CS616/CS625 output period

(microseconds) and an independently determined volumetric water content.

From this data, the probe response to changing water content can be described

by a quadratic calibration equation of the form

( )

θ τ τ τ

C C C= + +

0 1 2

* *

with

being the volumetric water content (m

-3

); τ , the CS616/CS625

period (microseconds); and C

, the calibration coefficient (n = 0..2).

The linear form is

( )

θ τ τ

C C= +

0 1

1 2 ... 37 38 39 40 41 42 43 44 45 46 47 48 49 50

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Campbell CS616 Manuel d'instructions Page 42

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