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The image intensifier in the IPCS is proverbially sensitive to
over-illumination. Pointing the the IPCS at a `bright' source - which can
mean only a few dozen photons per pixel per second - would destroy the
intensifier immediately; the intensifier is not readily replaceable.
Pointing the detector at a moderately bright source may cause no permanent
damage but may reduce its performance for the rest of the night.
To guard against disaster, a `panic button' is provided on the observing desk.
Pressing the panic button closes the IPCS shutter immediately.
The situation is particularly critical when the IPCS shutter is under system
control, as it must be for the DAS commands to work correctly. You should
note the following points:
- The resolved output from the IPCS is shown in real time on the DMS
display; the raw photon events are usually shown on an oscilloscope
connected directly to the IPCS camera. These displays show you
whether the light level is safe; if you are new to the IPCS,
please discuss with ING staff what constitutes safe illumination.
- The intensifier is vulnerable whenever the IPCS shutter is open, even
if DMS is not counting photons.
- Whenever you slew to a new source, the shutter must be closed. The
risk of a bright object tracking across the field of view is too
high to risk leaving the shutter open.
- Whenever you open the shutter, be prepared to shut it again with the
panic button.
- During an observation, the DMS may be receiving photon events from
a small part of an intensifier. Before opening the shutter on a
new source, give the overscan command so that you see as much
of the detector surface as possible.
- At the start of each observation, the system will open the shutter if
the context of the observation requires it and you should be ready to
use the panic button if necessary. It's unwise to put shutter-moving
commands at the end of a long queue.
The following safety features are built in to the system:
- When the system needs to open the shutter, it will warn you and
give you five seconds grace to get to the panic button.
- You can move the shutter at any time with (non-queuing) command
shutter <channel> <state> where state is open or closed.
- If you close the shutter with the panic button, it is taken out of
computer control until you give the command
shutter <channel> closed or an equivalent engineering command.
- The dome lights cannot be switched on when the IPCS is active.
However, this interlock can be disabled for engineering work, so
you should not rely upon it.
Previous: Interactive exposures
Up: Using the DAS
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Next Page: The observing log