[evlatests] Antenna/ACU/servo behavior in OTF mosaic tests

[Barry Clark]

Has anybody tried dec +89, moving 2d/sec in RA?

On 05/22/2016 04:44 PM, Vivek Dhawan wrote:
> An update on ACU behavior during fast tracking (OTF-mode). Issues found
> in previous tests are listed, with their current status. Plots exist to
> support these assertions, but are not attached here.
>
> 1. Interpolation of commands was incorrect (to all ACUs) near azimuth due
>     South, when tracking in the counter-sidereal direction.
>
>     This was fixed in the executor.
>
>
> 2. Tracking error (deviation from commanded position) had a significant DC
>     offset plus oscillations, in azimuth, especially on the NEW ACUs  ea01,
>     14, 17, 21. For these units, Doug W. has tuned the bias currents (in AZ
>     only, I believe) and eliminated most of the oscillation.
>
>     The elevation errors remain, ~1’ deviation, and seem to be random, i.e.
>     they are not antenna or servo resonances. There are differences between
>     antennas, its likely this too be tuned away: ea01 and 17 have large
>     EL rms, ea14 and 21 are very much better.
>
>     All 4 new ACUs have a DC tracking offset when we calculate the error
>     = (Position - Command) from the logged pointing data, but do not show
>     the offset on the error signal that drives the servo. This still needs
>     to be clarified, it may be another timing issue (distinct from OLD ACUs
>     in item 3).
>
>     The settling time for new ACUs is ~3sec, a factor of  ~2 better than
>     the old ACUs, and unchanged from before the tuning.
>
>
> 3. OLD ACUs had small tracking errors and no oscillations, but showed jumps
>     in the calculated error, ascribed to timing slop in labeling the
> current
>     command, future command, and measured position (in the MIB).
>
>     Hichem has updated the MIB code (on old ACUs) to fix the data handling,
>     and these timing errors are now eliminated. This code has been tested
>     on the sky, on a subset of antennas, but is not yet deployed anywhere.
>
>
> 4. The command sequence for OTF rasters was examined in detail, refined,
>     and tested again on May 19, near transit, 77deg EL, and at ~40deg El.
>     Bryan is looking at this, I believe it looked good.
>
>
> 5. MCAF (in test version) is writing the pointing table in binary form,
>     and as of Friday, Rich had successfully read these into CASA.
>     Promotion of test MCAF to production is expected soon.
>
>
> In summary,
>
> OLD ACUs : Look good to go, after the MIB update is deployed.
>
> New ACUs : Look good in AZ, need some tuning in EL. DC offset between
>             external and internal error signals needs to be understood.
>
> --------------------------------------------------------------------------
>
>
>
> _______________________________________________
> evlatests mailing list
> evlatests at listmgr.nrao.edu
> https://listmgr.nrao.edu/mailman/listinfo/evlatests