Campbell Scientific CS616 CS616 and CS625 Water Content Reflectometers - Page 42

Collecting Field Data for Calibration

Get Campbell Scientific CS616 PDF manuals and user guides View all Campbell Scientific CS616 manuals
Add to My Manuals
Save this manual to your list of manuals

Page 42 highlights

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. θg = mwet − mdry mdry For the bulk density ρbulk = mdry volumecylinder 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 θv = θg *ρbulk 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 θv (τ) = C0 + C1 * τ + C2 * τ2 with θv being the volumetric water content (m3 m-3); τ , the CS616/CS625 period (microseconds); and Cn , the calibration coefficient (n = 0..2). The linear form is θv (τ) = C0 + C1 * τ 36

  • 1
  • 2
  • 3
  • 4
  • 5
  • 6
  • 7
  • 8
  • 9
  • 10
  • 11
  • 12
  • 13
  • 14
  • 15
  • 16
  • 17
  • 18
  • 19
  • 20
  • 21
  • 22
  • 23
  • 24
  • 25
  • 26
  • 27
  • 28
  • 29
  • 30
  • 31
  • 32
  • 33
  • 34
  • 35
  • 36
  • 37
  • 38
  • 39
  • 40
  • 41
  • 42
  • 43
  • 44
  • 45
  • 46
  • 47
  • 48
  • 49
  • 50
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.
θ
g
wet
dry
dry
m
m
m
=
−
For the bulk density
ρ
bulk
dry
cylinder
m
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
v
C
C
C
=
+
+
0
1
2
2
*
*
with
θ
v
being the volumetric water content (m
3
m
-3
);
τ
, the CS616/CS625
period (microseconds); and C
n
, the calibration coefficient (n = 0..2).
The linear form is
(
)
θ
τ
τ
v
C
C
=
+
0
1
*
36