Pictures of azencoder a 270 marker
The azimuth has an encoder on each side of the
encoder rack gear. encoder 1 is on the dome side and is used for
pointing the telescope. encoder 2 is on the ch side and is used to
measure the bending of the azimuth arm.
A reference scribe mark has been placed at 270
degrees on the ring girder. The telescope can be moved to az=270 and
then a pointer (on the azimuth arm) can be slid out to meet this
reference mark. When changing encoder 1, we can use this reference mark
to make sure we come back to the same encoder value.
Pictures were taken of the pointer and pointer to
use as references. The correct position for the pointer on the
reference mark is whereever it was when the last pointing model was
- The correct position for the pointer, scribe is whereever it was
when the last pointing model was made.
- Looks like the scribe mark is about 1.5 mm wide
- The radius of the encoder is about 60 Ft.
- a 1 mm position error at the pointer is:
|az encoder error
|11.3 (little circle)
|on the sky za=5
|on the sky za=10
|on the sky za=15
|on the sky za=19.6
- We probably need to see how repeatable the encoder is by moving
back to 270 at a different day.
26jan12 - Encoder 1 replaced
If the pictures are correct, the az encoder moved by
1.5 mm or 15 asecs on the encoder. this is about 4.5 asecs at za=15.
26jan12 encoder 1 replaced. Equipment, bearings holding encoder were
- the encoder was full of grease. The maintenance crew should not
be greasing the encoder mount since the grease gets into the encoder.
- the bearings in the mount holding the encoder were damaged,
some were missing. It was rebuilt.
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