Topcon GPT-7500 Series, Instruction Manual

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6 CHECK AND ADJUSTMENT
6 CHECK AND ADJUSTMENT
6.1 Checking and Adjusting of Instrument Constant
Normally, the instrument constant does not have discrepancy. It is recommended you measure and
compare with an accurately measured distance at a location where the precision is specifically
monitored on a consistent basis. If such a location is not available, establish your own base line over
20m (when purchasing the instrument) and compare with the data measured with newly purchased
instrument.
In both cases note that the setup displacement of the instrument position over the point, the prism,
baseline precision, poor collimation, atmospheric correction, and correction for refraction and earth
curvature determine the inspection precision. Please keep in mind these points.
Also, when providing a base line in a building, please note that the difference in temperature greatly
changes the length measured in the building.
If the difference between the measured length of the baseline and the actual length exceeds the range
of the nominal accuracy, change the instrument constant of the prism mode according to the following
procedure.
1) On a basically horizontal line of about 100 meters, line AB, establish point C. Measure each
distance, AB, AC and BC, about 10 times, and calculate the average value for each.
2) Repeat Step 1 several times. Then calculate the variance with the current instrument constant (
Δ
K).
Δ
K = AB - (AC + BC)
3) Calculate the new instrument constant according to the formula below. Then reset the instrument
constant according to Section 6.4 “How to Set the Instrument Constant Value” .
New instrument constant = current instrument co
Δ
K
4) Once again, measure the baseline and compare the results to the baseline’s actual length. If the
difference between the two is within the range of the nominal accuracy, change the instrument
constant of the non-prism mode and the instrument constant of the non-prism long mode according
to the formula in Step 3.
5) If the results of the measurement conducted in Step 4 exceed the range of the nominal accuracy,
contact TOPCON or your TOPCON dealer.
6.1.1 Checking of the accuracy of the non-prism mode / non-prism long mode
If you reset the instrument constant, you must check the accuracy of the non-prism mode/non-prism
long mode.
Non-prism mode
1) Set a prism 30 to 50 meter apart from the instrument and measure the distance to the prism by
prism mode.
2) Take off the prism and set a (white) board.
3) Change the mode to the non-prism mode and measure the distance to the board.
4) Repeat above procedure and measure some points.
If the difference of the prism mode and non-prism mode is the range of ±10mm even one time, the
instrument is normal.
If the difference is never the range of
±10mm, contact TOPCON or your TOPCON dealer.
Non-prism long mode
1) Set a prism 30 to 50 meter apart from the instrument and measure the distance to the prism by
prism mode.
2) Take off the prism and set a (white) board.
3) Change the mode to the non-prism long mode and measure the distance to the board.
4) Repeat above procedure and measure some points.
If the difference of the prism mode and non-prism long mode is the range of ±20mm even one time,
the instrument is normal.
If the difference is never the range of
±20mm, contact TOPCON or your TOPCON dealer.
Note: Each of the Prism mode, Non-prism mode and Non-prism long mode has instrument
constant. You must obtain the instrument constant of the prism mode.
If you change the instrument constant of the prism mode, be sure to change the instrument
constant of the non-prism mode and the instrument constant of the non-prism long mode
by the same amount.
A
C
B