SciOp Procedure:

SOFI grism wheel: observational strategy and recovery procedures

Keywords: SofI - Grism Wheel - Observations - Recovery
Prepared/Revised: psinclai 2004-10-4 Reviewed: Released: epompei 2004-10-19


A software modification (thanks Ismo!) is taking care of the step motion of the grism wheel so during the operations it is not necessary to move the wheel by three steps by hand anymore.

Grism wheel recovery

Currently, the grism wheel suffers from a mechanical problem that prevents a smooth movement in the reverse direction (decreasing encoder number), which results in lost steps on the stepper motor, and consequently, loosing the encoder value calibration. In slow speed (below 1000), the wheel does not move at all in the reverse direction. A configuration changes have been made by software, making it possible to use the wheel.
-- One change was to the direction of the anti-backlash compensation which controls from which side the wheel approaches to the final position. By reversing that value, the wheel now approaches always into the positive direction, i.e going from position 1 (wollaston 88611) to position 8 (open, 57627). To check the wheel alignment,you can send it to the Wollaston position (88611) which will move the wheel in + direction (from open) and will allow to check the alignment if the JG Mask is also set.
-- The other change is constrains the grism motion to steps no larger than three positions: i.e. every three (or two/one in some cases) positions the wheel pauses before it continues to the final position.


Procedure to follow if the grism wheel was in simulation and it is needed again (Procedure A)

Procedure to follow if the grism wheel is not needed any longer and has to be moved to Simulation (Procedure B)

Observational strategy

The new software modification has made it unnecessary to move the grism wheel bu hand. HOWEVER, you need to monitor the motion of the wheel to ensure it follows the "no-more-than-three_steps-at-a-time" and "no-reverse-motion" rules.
To do thatm start the isiMonitor tool from any xterm on the wsofi. It will start 2 plots: one for encoder position (left panel) of the grim wheel and one for speed (right panel) of the grism wheel.
nEhe eoder position plot should always be increasing (expect when the maximum value is reached; then is jumps all the way down to zero). The plot is configured to have all circular range of grism wheel, so line should go down only when upper side of the plot is reached and then start increasing again.
The speed plot on the right should be always greater or equal than zero.
In case you detect negative movements, you have to call software support ASAP to recover old version. And after it is recovered, you have to manually restrict movements again only max. 3 steps for the grism wheel (and possible aligning the grism wheel is needed) The old version of this page that explains how to operate the grism wheel with the previous version of the software that requires to move it only in steps of up to three positions is still available here.
Please, note down starting and target positions, and template name in case of failure.

Appendix: SOFI LCU reboot (Procedure C)

What to do in case of LCU reboot:

Appendix: SOFI FB Init (Procedure D)

How to do a FB (fall-back) Init?


[ESO |LaSilla |SciOp |SciOpInternal ]