The "tilt_meter" command.

tilt_meter [state=on|off, limit=?]

Specify how and if the azimuth tilt meters are to be used.

Mandatory Arguments:

(none)

Optional Arguments:

SwitchState state: If this argument is on, then the azimuth tilt meter readouts will be used to correct the pointing. If it is off then they will be ignored. In the archive the tracker.corflags register can be used to determine whether this tilt correction was enabled.
AngleLimit limit: If the magnitude of either tilt meter readout is greater than this number, then the tilt correction won't be made and the overflow condition will be recorded in the tracker.corflags register.

Example 1:

The following example enables the use of the tilt meters in the pointing model, and specifies that if either of the tilt meter outputs is outside of the range -100..100 arcseconds, this will be considered an error.

 tilt_meter state=on, limit=0:1:40

Example 2:

The following example stops the tilt meter from being used in the pointing model.

 tilt_meter state=off

Context:

In addition to a fixed misalignment of the azimuth axis, the azimuth axis also tilts by varying amounts as the ground beneath the telescope shifts and as the load on the front of the azimuth platform changes with elevation. The former fixed tilt is corrected by a constant term in the pointing model, whereas the varying tilt is computed from on-line measurements of tilt meters located on the azimuth platform. This command enables or disables the use of the tilt meters to correct for the variable tilt.

To prevent a broken tilt meter from sending the telescope all over the sky, a readout limit is required.

Note that the tilt meter is disabled and has a limit of zero degrees when the system starts. An example of a suitable limit would be about 100 arcseconds. The appropriate limit could be set in the reboot file (see load_reboot_script).

Martin Shepherd (6-Jul-2000)