4 Checking and Adjustment
50 Spectra Precision Focus 8 Series Total Station User Guide
Checking the instrument constant
The instrument constant is a numerical value used to automatically correct for the
displacement between the mechanical and electrical centers when measuring
distances. The instrument constant is set by the manufacturer before the instrument is
shipped. However, to ensure the highest operational accuracy, we recommend that you
check the instrument constant several times a year.
To check the instrument constant, you can either compare a correctly measured base
line with the distance measured by the EDM, or follow the procedure below.
To check the instrument constant:
1. Set up the instrument at Point P, in as flat an area as possible.
2. Set up a reflector prism at Point Q, 100 m away from Point P. Make sure that you
take the prism constant into account.
3. Measure the distance between Point P and Point Q (PQ).
4. Install a reflector prism on the tripod at Point P.
5. Set up another tripod at Point R, on the line between Point P and Point Q.
6. Transfer the Focus 8 series instrument to the tripod at Point R.
7. Measure the distance from Point R to Point P (RP), and from Point R to Point Q
(RQ).
8. Calculate the difference between the value of PQ and the value of RP + RQ.
9. Move the Focus 8 series instrument to other points on the line between Point P
and Point Q.
10. Repeat
Step 5 through Step 9 ten times or so.
11. Calculate the average of all the differences.
The error range is within 3 mm. If the error is out of range, contact your dealer.
About 100 m
PQ
PRQ
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