Topcon GPT-7500 Series, Instruction Manual

Page: 108 / 134

106
8 SETTING ATMOSPHERIC CORRECTION
8 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.
8.1 Calculation of Atmospheric Correction
GTS-750
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
GPT-7500
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
Ka
: Atmospheric correction value
P
: Ambient atmospheric pressure (hPa)
t
: Ambient Atmospheric temperature (°C)
Ka
279.67
79.535
P
×
273.15 t +
--------------------------- –
⎩ ⎭
⎨ ⎬
⎧ ⎫
10
6 –
×
=
Ka
279.67
79.535 847
×
273.15 20
+
--------------------------------- –
⎩ ⎭
⎨ ⎬
⎧ ⎫
10
6 –
×
=
Ka
: Atmospheric correction value
P
: Ambient atmospheric pressure (hPa)
t
: Ambient Atmospheric temperature (°C)
Ka
279.85
79.585 P
×
273.15 t +
--------------------------- –
⎩ ⎭
⎨ ⎬
⎧ ⎫
10
6
–
×
=
Ka
279.85
79.585 847
×
273.15 20
+
--------------------------------- –
⎩ ⎭
⎨ ⎬
⎧ ⎫
10
6 –
×
=