12-1
12 SETTING ATMOSPHERIC CORRECTION
12
SETTING ATMOSPHERIC CORRECTION
The velocity of light through air is not constant and depends on the atmospheric temperature and
pressure. The atmospheric correction system of this instrument corrects automatically when the
correction value is set. 15
°
C/59
°
F, and 1013.25hPa/760mmHg/29.9 inHg is as a standard value for
0ppm in this instrument. The values are kept in the memory even after power is OFF.
12.1 Calculation of Atmospheric Correction
The followings are the correction formulas.
Unit; meter
The distance L (m) after atmospheric correction is obtained as follow.
L = l (1+Ka)
l: Measured distance when atmospheric
correction is not set.
Example: In case Tempe20°C, Air pressure 847hPa, l =1000 m
+
50
×
10
-6
(50 ppm)
L
= 1000 (1+50
×
10
-6
) = 1000.050 m
12.2 Setting of Atmospheric Correction Value
How to Set Temperature and Pressure Value Directly
Measure the temperature and air pressure surrounding the instrument beforehand.
Example: Temperature: +26°C, Pressure: 1017 hPa
Operating procedure
Operation
Display
1
Press the [F3](S/A) key to set Set Audio Mode
from distance or coordinate measurement mode.
[F3]
2
Press the [F3](T-P) key.
[F3]
3
Input Temp.value and Pressure value.*1)
Mode returns to Set Audio mode.
Enter Temp.
Enter Pres.
*1) Refer to Section 2.5 “How to Enter Alphanumeric characters”.
Range: Temp. –30 to +60°C (0.1°C step) or –22 to +140°F (0.1°F step)
Pres. 560 to 1066.0hPa (0.1hPa step) ,420 to 800mmHg (0.1mmHg step) or
16.5 to 31.5inHg (0.1inHg step)
When the atmospheric correction value which is calculated from the input temperature and pressure
values exceeds the range ± 999.9ppm, the operating procedure returns to step
3
automatically. Input
values again.
Ka
: Atmospheric correction value
P
: Ambient atmospheric pressure (hPa)
t
: Ambient Atmospheric temperature (°C)
Ka
279.67 79.535
x
P
273.15
t
+
--------------------------
–
x
10
6
–
=
Ka
279.67 79.535
x
847
273.15 20
+
--------------------------------
–
x
10
6
–
=
SET AUDIO MODE
PSM:0.0 PPM 0.0
SIGNAL:[
IIIII
]
PRISM PPM T-P –––
TEMP. & PRES. SET
TEMP.
=
15.0 °C
PRES. : 1013.2 hPa
––– ––– [CLR][ENT]
TEMP. & PRES. SET
TEMP. : 26.0 °C
PRES.
=
1017.0 hPa
––– ––– [CLR][ENT]
