Sokkia CX-101, Руководство по обслуживанию, Страница: 267 / 322

257
33. CHANGING THE SETTINGS

Atmospheric correction factor
The velocity of the light beam used for measurement varies according
atmospheric conditions such as temperature and air pressure. Set the
atmospheric correction factor when you wish to take this influence into
account when measuring.
• The CX is designed so that the correction factor is 0 ppm at an air pressure
of 1013 hPa, a temperature of 15
°
C, and a humidity of 50%.
• By inputting the temperature and air pressure values, the atmospheric
correction value is calculated using the following formula and set into the
memory. (humidity is regarded as 50%)
t : Air temperature (
°
C)
p : Pressure (hPa)
e : Water vapor pressure (hPa)
h : Relative humidity (%)
E : Saturated water vapor pressure
• e (water vapor pressure) can be calculated using the following formula.
With constant pressure, a temperature change of 1
°
C: an index change of
1 ppm.
With constant temperature, a pressure change of 3.6 hPa: an index change
of 1 ppm.
To perform high accuracy measurements, it is necessary to find the
atmospheric correction factor from even more accurate temperature and
pressure measurements and perform an atmospheric correction.
It is recommended that extremely precise instruments be used to monitor
the air temperature and pressure.
• Determine the temperature and pressure as follows.
Flat terrain :Use the temperature and pressure at the midpoint of
the line.
Mountainous terrain :Use the temperature and pressure at the
intermediate point (C).
282.324
0.294362 p ×
1 0.003661 t
×
+
------------------------------------------ –
0.04127 e ×
1 0.003661 t
×
+
------------------------------------------ +
Atmospheric Correction Factor (ppm) =
E 6.11 10
7.5 t
× ( )
t 237.3 +
( )
----------------------------
× =
e h
E
100
----------
×
=