EPOX ET106 Series Manuel d'utilisateur télécharger pdf (Page 4)

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Water content reflectometer gives improved accuracy

The CS616 water content reflectometer (shown

with the CR10X) improves upon the measure-

ment accuracy of the CS615 while matching

its resolution and precision.

View data without

opening enclosure

with the CD294

Campbell Scientific Australia’s CD294

“DataView” is a two-line, 32-character

LCD that displays a datalogger’s real-time

input location value, its description, and

measurement units. Two buttons allow

you to scroll through 20 selected input

locations. The CD294 is synchronized to

the datalogger's Table 1 execution inter-

val, so measurements can be displayed as

they are made.

To conserve power, the DataView goes

into a low power mode that draws only 12

microamps if a button has not been

pressed within two minutes. The CD294

is designed to mount into the lid of an

environmental enclosure; a template for

an enclosure cutout, mounting screws, and

O-rings are provided. The DataView is

easily programmed using PC294W soft-

ware and a PC programming cable, both

of which are included.

Campbell Scientific and the USFS

Rocky Mountain Research Station

have collaborated in the development

of a duff moisture meter. Foresters

and other land managers can use the

DMM600 to make decisions for pre-

scribed burns and fire fighting.

The water content of duff is an

important factor in the propagation of

fires (duff is decaying leaves and other

forest litter that covers the forest

floor.). Historically, duff water content

was determined by collecting field

samples in plastic bags and transport-

ing the samples to a laboratory for

analysis. The DMM600 allows quick

and accurate on-site measurements

using circuitry similar to our water

content reflectometers.

To begin the measurement

process, duff is placed in the

measurement chamber of the

DMM600. The crank is turned

by hand to compress the sample

to the measurement density, and

the reading is automatically taken.

Volumetric water content measure-

ments derived from a standard calibra-

tion and one user-defined calibration is

alternately displayed until the sample

is removed. The time required to

determine water content is essentially

the time required to load the sample.

The actual measurement time is only

tens of milliseconds.

the DMM600 is portable and robust

enough for field use. It has a 3.5 inch

diameter, is 10 inches long, and

weighs approximately 3.7 pounds.

The DMM600 will be available in

March, 2002.

Assess duff moisture on-site

design and use of new surface-mount

electronic components that provide better

high-frequency performance. The CS616

can be ordered with lead lengths up to

1000 feet.

Like the CS615, the CS616 consists of

two 30 cm stainless steel rods that con-

nect to an epoxy-encapsulated printed cir-

cuit board. The differentially driven rods

form a transmission line with a wave

propagation velocity that is dependent on

the dielectric permittivity of the medium

surrounding the rods. Nanosecond rise-

times produce waveform reflections char-

acteristic of an open-ended transmission

line.

The return of the reflection from the

rod ends triggers a logic state change that

initiates propagation of a new wavefront.

Since water has a dielectric permittivity

significantly larger than other soil con-

stituents, the resulting oscillation frequen-

cy is dependent upon the average water

content of the medium surrounding the

rods.

The megahertz oscillation frequency is

scaled down and easily read by Campbell

Scientific's CR510, CR10X, CR23X or

CR5000 dataloggers. The probe rods can

be inserted from the surface or buried at

any orientation to the surface.

Avoid the time delay and expense of lab

analyses with the DMM600.

Each CS616 requires a single-ended

input channel along with a control port to

enable the probe. Multiple probes can use

a single control port. Instruction 138 has

been developed to measure the CS616

with the CR510, CR10X, and CR23X;

measurement time is approximately

0.5 milliseconds. The period averaging

instruction, 27, can also be used with the

CR510, CR10X, and CR23X dataloggers.

The CR5000 uses the PortSet and

PeriodAvg instructions to measure the

probe. Consult our product literature for

versions of PC208W, LoggerNet, and dat-

alogger OS that support Instruction 138.

Operating specifications (VWC =

volumetric water content)

• probe-to-probe variability: ±0.5%

VWC in dry soil, ±1.5% VWC in

typical saturated soil

• accuracy ±2% VWC using standard

calibration with bulk electrical

conductivity ≤ 0.5 deciSiemen

meter

-1

in the 0% to 50% VWC

measurement range

• precision 0.05% VWC

• resolution 0.1% VWC

A new version of the Water Content

Reflectometer, the CS616, is available

from Campbell Scientific. The CS616

improves upon the measurement accuracy

of the CS615 while matching its resolu-

tion and precision. New features include

improved electrostatic discharge protec-

tion and reduced measurement time and

sensitivity to signal attenuation. The

improvements come from a refined circuit

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EPOX ET106 Series Manuel d'utilisateur Page 4

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