SHANGHAI ESURVEY GNSS CO., LTD.
97
7 Check and Correction
7.1 Instrument Constant
Before delivery, the distance plus constant of the instrument has been calibrated to zero.
Considering the distance plus constant may change, it shall, if possible, be subject to
regular precise measurement based on the existing baseline, or if impossible, be
measured by using the following method:
Note: Both centering error and collimation error of the instrument and prism may
affect the measurement result of distance plus constant, and thus special care should be
taken to reduce these errors during inspection. Besides, it is also required to make the
instrument and prism of equal height, and a level should be used to measure the
instrument height and the prism height when detection is performed on uneven ground.
1. Select two points A and B on the flat ground that are about 100m away from each
other, respectively set the instrument and a prism at points A and B, and select a
point C between points A and B:
2. Precisely measure the horizontal distance between A and B for 10 times, and
calculate the average value.
3. Move the instrument to C, and set prisms at points A and B:
4. Precisely measure the horizontal distance between C and A and between C and B
for 10 times, and respectively calculate average values.
5. Calculate the distance plus constant according to the following formula:
K = AB - (CA + CB)
6. Repeat step 1 ~ 5 to measure the distance plus constant for two to three times:
o If the results always fall within ±3 mm, no correction is required.
o If not, correction is required.
At this time, please contact us.
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