19. CHANGING THE SETTINGS
118
• Atmospheric correction factor is calculated and set using the entered values of the temperature
and air pressure. Atmospheric correction factor can also be entered directly.
• When the settings here are different between basic mode and program mode, program mode
settings are prior for use.
Items set, options, and input range (*: Factory setting)
Temperature
: -30 to 60°C (15*), -22 to +140°F (59*)
Pressure
: 500 to 1400hPa (1013*), 375 to 1050mmHg (760*),
14.8 to 41.3 (inchHg) (29.9*)
Humidity
: 0 to 100% (50*)
ppm (Atmospheric correction factor)
: -499 to 499 (0*)
• The "Humidity" item is displayed only when the "ppm setting" in "Obs. condition" is set to
"+Humidity".
• When 0.1mm is selected in "Dist.reso", values can be input to the first decimal place.
&
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 instrument 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, air pressure values and humidity, the atmospheric correction
value is calculated using the following formula and set into the memory.
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.
• The instrument measures the distance with a beam of light, but the velocity of this light varies
according to the index of refraction of light in the atmosphere. This index of refraction varies
according to the temperature and pressure. Near normal temperature and pressure
conditions:
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.
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
----------
×
=
