Campbell Scientific DOT600 Roadbed Water Content Meter - Manual (Page 23)

Appendix A. Design and Calibration
Calibrating the DOT600 scale is a simple matter of placing objects of known
weight on the scale and recording the output voltage. Precision calibration
weights manufactured by Ohaus and checked on an independent scale were
used. Figure 1 show the linear relationship
Weighing scale calibration
y = 1065x - 80.773
R 2 = 1
-100
0
100
200
300
400
500
600
700
0.000 0.100 0.200 0.300 0.400 0.500 0.600 0.700
voltage output (V)
w
ei
ght
(
g
)
FIGURE A-1. Typical scale calibration. The standard error is 0.013 g.
A.4 Displacement Sensor Calibration
Magnetic displacement sensors provide position of both the compression piston
and the plate above the compression springs. With the information both
sample chamber volume and compression force can be derived. Calibration of
the displacement sensors was performed by placing spacers of known length in
the sample chamber and calibrating to measurement output voltage. The
spacers were custom made with tolerance +/- 0.0005 inch. The error from the
calibration and other error sources is considered in the performance
specifications. Figure 2 show a typical displacement sensor calibration.
Polynomial equations were used to define the calibration equations for all
sensors.
A-3