Background

This document describes the procedure for changing a DEIMOS grating when the grating system is not able to reach an unload position by itself. The workaround described here involves using keyword-level commands to position the grating select stage and grating tilt independently.

Procedure

Command the grating select stage to the unload position using the command:
```
	modify -s deimot grselord=-3
```
for grating 3 unload, or
```
	modify -s deimot grselord=-4
```
for grating 4 unload.

Command the grating tilt to the unload position by using any of the following commands:

Grating 3	Grating 4
modify -s deimot g3tltraw=-75000	modify -s deimot g4tltraw=-80300
modify -s deimot g3tltord=-1	modify -s deimot g4tltord=-1
modify -s deimot g3tltnam=Unload	modify -s deimot g4tltnam=Unload

Once you succeed in getting the grating to that position, be sure to turn off servo power to the G3 tilt drive motor via:
```
	modify -s deimot g3tltmod=halt
```
This is necessary to prevent damage to the tilt motor!
Remove the old grating.
Insert the new grating and scan the barcode label.
Re-enable the G3 tilt drive motor by:
```
	modify -s deimot g3tltmod=pos
```