Encoder failures during 2007


11apr07 encoder 1 failure
08apr07 encoder 1 failure

11apr07:azimuth summary plots (.ps) (.pdf)
08apr07: azimuth summary plots (.ps) (.pdf)
08apr07: pointing errors caused by the failure (.ps) (.pdf):


        The azimuth arm has 2 encoders. They are situated on opposite sides of the azimuth arm by the encoder rack gear. The encoder on the gregorian dome side (az encoder 1)  is used for pointing. The encoder on the carriage house side (az encoder 2) is used to measure the bending of the azimuth arm.
    If az encoder 1 fails then the system switches to az encoder 2. This allows continued operation with degraded pointing accuracy. As the azimuth rotates, the azimuth arm bends slightly. The pointing is servoed to the encoder on the dome side. The encoder on the ch side will be off from encoder 1  by the bending amount. This changes depending on the direction the motors are driving the azimuth.
    We have been having a number of azimuth 1 encoder failures recently. The system has  continued running using az encoder 2 (and degraded pointing). Some observations are: .

The Failures.  (top)

11apr07: Az 1 encoder failure

       The azimuth 1 encoder failed twice during the morning of 11apr07. The failures occurred at 2:35 and  5:30 am. The operator was able to reset the errors remotely. The two failures occurred at: az=203,za=5.5 and az=332.4,za=14.999.
   The azimuth summary plots (.ps) (.pdf) show the failure:
    Processing: x101/070411/chkaz.pro

08apr07: Az 1 encoder failure

    The failure occurred at 12:33. The azimuth was sitting at 270 degrees and the dome was at za=10 degrees.

The azimuth summary plots (.ps) (.pdf) show the failures:

The pointing errors caused by the failure (.ps) (.pdf):
Processing: x101/070408/chkaz.pro

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