Puerto rico experienced a number of strong
earthquakes starting on 6jan20 through 11jan20 (see
a list of quake, strength, cable/tilt sensor oscillation freq).
After the first quake on 6jan20 the telescope was parked with the
motors off and the brakes on (except for one or 2
instances). The az encoder (read once a second) showed that
the azimuth arm moved during each of the stronger quakes. This is
to be expected since:
- The azimuth flanged wheels sit on the azimuth rail.
- the brakes will keep the wheels from turning, but the wheels
can still slide on the azimuth rails if the force overcomes the
static friction between the wheels and the rail.
- The azimuth arm rotates about a central bearing. We need to be
careful that there is not too much bending in the azimuth
arm because of some differential motion in the carriage
house and gregorian dome sides of the azimuth arm.
- the carriage house and the dome do not have this problem since
they are pulled up and down the azimuth arm via a geared track.
Some occurrences that may have moved the telescope (times are ast
|telescope was moving during quake
|operator moved dome .03 degrees
|observer moved telescope
az .3 deg
dome: .03 deg
After about 20 minutes they returned az,gr to original
Plots were made showing the motion of
the telescope 6 jan to 28 jan20. (.pdf)
- Page 1: azimuth positions, az encoder differences 6jan to
- top: azimuth position
- The times when the azimuth moved is flagged with an
adjacent label with the strength of the quake.
- The largest jump was the 5.9 quake of 11jan20, where the
azimuth moved more than .1 degrees.
- After a power outage, the azimuth value can drop off the
page (system needs a reset).
- bottom azimuth encoder difference (azgr - az ch).
- The largest jump was the 5.9 quake of 11jan20. It moved
about .01 degrees.
- Page 2: greg dome and carriage house za position.
- Top: dome za.
- The 6.4 quake showed a .03 deg change in the encoder.
- This turned out to be the operator entering the
pntpwrdip command after the power came back. This turns on
the motors and caused the dome to move by .03 degrees.
- The only other dome motion was on 22jan20 around 18:00.
The observer started cima and moved the telescope .03 degree
(to the position it had on 06jan20). After about 20 minutes
they moved it back to the 8.03 deg position.
- bottom: carriage house za.
- there was no motion of the ch.
- Page 3-4. these are blowups of the az position and az encoder
difference for the stronger quakes.
- page 3 frame 1,2 - 07jan20 6.4 quake.
- the power dropped out for about 6 minutes (the generators
came on and it took the operator awhile to reset things.
- Looking at the motor status i saw that the dome motors
were turned on for a few second but the azimuth motors
were never started.
- page 3 frame 3,4 07jan20 5.6 quake
- the azimuth moved by about .06 degrees.
- page 4 frame 1-2 5.2 quake 10jan20
- no motion of the azimuth position.
- page 4 frames 3-4 5.9 quake 11jan20
- the azimuth moved by .14 degrees
- the encoder difference changed by about .01 degrees .. so
the azimuth bending changed a little
- Page 5 blowup of dome za
- there was a .03 degree move on 07jan20 caused by the
- there was a -.03 and then .03 move on 22jan22 caused by the
observer (lasting about 20 minutes)
- Other than these 2 moves, the dome remained in the same
position to within .0006 degrees
- Using a radius of 420.75 feet (128.245m) from the center
of curvature to the rolling surface, a .0006 degree
motion is 1.3 mm
- With the motors off and the brakes on, the azimuth slid by up
to .14 degrees during some of the earthquakes
- using a 60 foot radius .14 degrees is 1.76 inches or 4.5 cm.
- there was a slight increasing in the bending during one of the
motions (.01 degrees).
- The azimuth position is measured with an encoder that rides on
an azimuth wrack gear.
- As long as the encoder remains engaged with the rack gear,
there is no loss of position information.
- On 30jan20 osvaldo and willie checked the azimuth position
using the scribe mark pointer (at az=270). They found that the
encoder value was correct (there was no jump of the encoder).
- the gregorian dome and ch did not slide during the quakes
since they run on a geared track.