Campbell Scientific DOT600 Roadbed Water Content Meter - Manual (Page 19)

DOT600 Roadbed Water Content Meter
6. Detailed Description
6.1 Power System
6.1.1 Battery, Charger and Power Switch
A 2.9 Ahr battery and a CH100 charger/regulator (manufactured by Campbell
Scientific) are mounted beneath the panel as shown in Figure 1.
A wiring harness distributes power and connects the charger to a jack located
on the panel in the upper-left corner near the power switch. This jack mates
with the wires from a wall transformer and allows charging the battery. The
2.9 Ahr battery will provide 24 hours of continuous operation. The battery will
not operate properly under 11.5V.
FIGURE 1. Cross sectional drawing shows mounting of battery and charger/regulator beneath panel.
6.2 CR850 Datalogger
The CR850 Measurement and Control Datalogger monitors all measurement
sensors, executes measurement program and stores the measurement results as
a time-stamped record. These operations are controlled by a custom datalogger
program designed by Campbell Scientific.
6.3 Water Content Measurement
6.3.1 Electronics and Waveguide
The water content measurement uses a method that is sensitive to dielectric
permittivity. The permittivity of water is at least an order of magnitude greater
than other soil constituents. Other than air, which has permittivity of one,
water is the only soil constituent that changes with time.
This method is sensitive to volumetric water content which is reported directly
by the datalogger. Conversion to gravimetric water content is calculated from
the wet weight, volume and volumetric water content.
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