Topcon GPT-2000 Manuel D’Utilisation

   12 SETTING ATMOSPHERIC CORRECTION

12-1

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.

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

●

Measure the temperature and air pressure surrounding the instrument beforehand.
Example : Temperature: +26°C, Pressure:1017 hPa

Press the [F4] key to get the soft key page 2 in the 
distance measurement mode or page 3  in the 
coordinate measurement.

[F4]

Press the [F3](S/A) key to set Set Audio Mode 
from distance or coordinate measurement mode.

[F3]

Press the [F3](T-P) key.

[F3]

Input Temp.value and Pressure value.*1)
Mode returns to Set Audio mode.

Enter Temp.

Enter Pres.

*1) Refer to Section 2.6 “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)

:  Atmospheric correction value

 :  Ambient atmospheric pressure (hPa)

 :  Ambient Atmospheric temperature (°C)

278.88 79.307 

 ×

273.15 

 +

-------------------------------

–

 











 10

6 

–

 

×

 

=

278.88 79.307 847 

×

273.15 20 

+

----------------------------------------

–

 











 10

6 

–

 

×

 

=

↓

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