Topcon GPT-8003A User Manual

11 SETTING ATMOSPHERIC CORRECTION
11-1
11 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.
• Setting the atmospheric correction value is in the STAR key ( ) mode.
11.1 Calculation of Atmospheric Correction
Operating procedure Operation Display
1 Press S
TAR ( ) key.
GPT-8000A series should be changed the
menu of star key mode to page three by
pressing the [F6] key twice.
[]
2
Press the [F3](GPT-8000 series) or [F2](GPT-
8000A series) key.
Current setting value is displayed.
[F3]
or
[F2]
3 Input Temp.value and press [ENT] key.
[Example] Temp. : +26
° C
The cursor moves to Pressure setting
automatically
Enter
value
[ENT]
2002-08-10 14:30:40
1
↓
GPT-8000 series
NP/P
2002-08-10 14:30:40
3 ↓
GPT-8 000A series
20.0 ° C
5.1ppm
1012.0hPa
23.6 mm
Tem p er ature setting
+14.0 mm
26.0 ° C
5.1ppm
+14.0 mm
1012.0hPa
23.6 mm
Pressure setting
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 Temperature +20
° 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
279.85
79.585
P
×
273.15
t
+
----- --------- -------- ----–



10
6–
×=
Ka
279.85
79.585 847×
273.15 20+
----- --------- -------- ---------–



10
6–
×=
11.2 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:1020 hPa

Topcon GPT-8003A Specifications

General

Brand	Topcon
Model	GPT-8003A
Category	Measuring Instruments
Language	English