Clara
20
Version 2.0 rev 24 Mar 2015
OPERATION
4.5.4 o
utput
daC
s
Voltages to control external devices from the Clara can be chosen by selecting the
Output DACs
function from the
Hardware
drop-down menu.
•
These DAC outputs allow the user to set an analogue voltage up for external devices.
•
The resolution can be set to 8,10,12,14 or 16 bits. Both DAC outputs can then be scaled to a maximum of
approximately 5V or 10V.
•
These do not provide absolute outputs and there will be slight variations between the two outputs.
•
Each voltage output can then be adjusted with up to 16 bit resolution. The maximum current which can be
drawn from these outputs is 10mA
4.6 t
iming
p
aRameteRs
Depending on which combination of Acquisition, Readout & Triggering modes is selected, various timing parameters are
available for the Clara as follows:
•
Exposure Time (secs)
•
No. of Accumulations
•
Accumulation Cycle Time (secs)
•
Cosmic Ray Removal
•
Kinetic Series Length
•
Kinetic Cycle Time (secs)
4.6.1 u
sing
s
HutteRs
When the Shutter Control option is selected from the Hardware drop-down-menu, or the
button is clicked, the
Shutter Control
dialog box opens e.g.:
You can use this to indicate when and how a hardware shutter should be used. With a CCD, the shutter is used for
background shuttering. Certain settings (e.g.
Permanently OPEN & Permanently CLOSED
) take effect as soon as you
close the Shutter Control dialog box. Other settings will be applied whenever you acquire data.
•
Fully Auto
is the simplest shutter mode, as it leaves all shuttering decisions to the system. When you perform
Take Signal the shutter opens for the duration of the Exposure Time you have entered in the Setup Acquisition
dialog box.
NOTE: This option will automatically provide suitable shuttering for the majority of data acquisitions. The shutter
will be closed for background data acquisitions and will be opened for all other data acquisitions.
•
If CLOSED for background
mode is selected, any shutter driven from the Shutter output will be closed as you
perform Take Background. If you want the shutter to be open so that the Take Background function records
genuine optical background data, deselect the option.
NOTE: Usually a background scan is used to subtract the dark signal and the Fixed Pattern Noise (FPN) of the
sensor. For this reason the background scan is usually performed in darkness. A shutter may be used to stop
light entering the spectrograph or other imaging system. Strictly speaking though, the background acquisition
may be regarded as comprising all light with the single exception of the source. Thus, when you are working with
a pulsed or independently shuttered source, it may be appropriate to have the mode deselected.
