LN2 Camera purge

[nickkonidaris]

To dislodge debris, and dry the valves from contaminants, we'd like to execute a "camera purge". A camera purge will be between 10 to 20 seconds (default baseline is 10 s), and we'd like to sequence events as:

• Camera Purge (10 s for each camera)
• Line Purge (20 minutes or so)
• Camera fill (3 minutes for each camera or so).

We'd like to be able to decide if we do the camera purge or not. Our baseline plan is to perform the camera purge in the evenings only. But we may decide to do it during all fills (or none). So I recommend we add a command like

ln2fill campurge-purge-and-fill -v FLOAT Camera purge time, in seconds. [required]

To test this, can you only test during the weekdays over the evening fills. Guillermo will be around next week, and you may be able to coordinate with him.