CS100 Barometric Pressure Sensor
9: Sample (P70)
1: 1
Reps
2: 1*
Loc [ P_mb ]
*Table 2 Program
02: 0.0000 Execution
Interval
(seconds)
*Table 3 Subroutines
End Program
-Input Locations-
1 P_mb
* Proper entries will vary with program and datalogger channel, and input location assignments.
7.3.4 Output Resolution
When storing the values from the CS100 to a data table or to a datalogger’s
final storage location, care must be taken to choose suitable scaling of the
reading, or to store the value with adequate resolution to avoid losing useful
resolution of the pressure measurement. The default resolution (low
resolution) for Campbell Scientific dataloggers is limited to a maximum of four
digits. Even then, the maximum digit value that can be displayed is 6999 for
Edlog dataloggers, and 7999 for the CRBasic dataloggers. If you use this
option with barometric data scaled in millibars (hPa), a reading above
799.9 mb for CRBasic dataloggers or 699.9 mb for Edlog dataloggers will lose
one digit of resolution, e.g. at 900 mb, the resolution is limited to 1 mb.
To retain 0.01 mb resolution, you either need to deduct a fixed offset from the
reading before it is stored to avoid exceeding the 799.9 for CRBasic
dataloggers or 699.9 for Edlog dataloggers threshold, or output the barometric
reading in high resolution format. This can be done by using the IEEE4 format
for the CR800, CR850, CR1000, CR3000, CR5000, and CR9000(X)
dataloggers or using the Resolution (P78) instruction for our Edlog
dataloggers. The default data output format for CR200(X) series datalogger is
IEEE4.
7.4 Correcting Pressure to Sea Level
The weather service, most airports, radio stations, and television stations adjust
the atmospheric pressure to a common reference (sea level). Equation 1 can be
used to find the difference in pressure between the sea level and the site. That
value (
dP
) is then added to the offset (600 mb in our example programs) in the
measurement instruction. U. S. Standard Atmosphere and dry air were
assumed when Equation 1 was derived (Wallace, J. M. and P. V. Hobbes,
1977:
Atmospheric Science: An Introductory Survey
, Academic Press,
pp. 59-61).
dP
E
=
− −
⎛
⎝
⎜
⎞
⎠
⎟
⎧
⎨
⎪
⎩⎪
⎫
⎬
⎪
⎭⎪
1013 25 1
1
44307 69231
5.25328
.
.
(1)
15
