plot scan
The command "plot scan" is a lower level command used internally by both the
commands "plot phase" and "plot flatten". A previously plotted section may be
scanned using this command to measure the plotted intensity on a channel by
channel basis. To cause the results to be written to the monitor at the end of
scanning be sure to set the verbose NVS parameter "plot" to one before starting.
Several NVS parameters affect the scanning process. In particular the head NVS
parameter "scands" sets the scanning drum speed. A suitable value for this is 10
RPM. If necessary, a higher speed may be used to get the PLL to lock thereby
sacrificing some signal to noise (ie. a lower drum speed is preferred). The
sys NVS parameter "newd" is automatically enabled while scanning if not
already enabled to provide the higher resolution drum velocity measurement
required when spinning the drum very slowly (see section on the drumservo
below). As a last resort if PLL lock is not obtained at slow drum speeds then
the sys NVS parameter "scanntu" can be set to try it with different ntu
values. If this parameter is zero then the scanning routines automatically
pick an ntu value derived from the regular ntu value and scaled for the
scanning drum speed. I expect that this will almost always work and hence
there will be no need to adjust the sys NVS parameter "scanntu" but it is there
just in case.
The best focus for the focus laser does not coincide with the best write laser
focus and thus the head NVS parameter "scanlpos" is used to set the lens
position while scanning. A suitable value is 200 assuming that the head was
set up so that the write laser focus is close to an lpos of 0. While scanning
the focus mode is internally set to 1 (lpos hold) and does not track the plate
surface. This is okay since the focus laser depth of focus is much larger than
for the write laser.
The offset parameter is in mil and the length parameter in 1/10th inches. The
last optional parameter is the scan mode. Two modes exist with mode 2 the
default. In mode 2 the channel information is preserved so this mode is needed
when building scorr tables. Mode 1 is used when only the overal density is
important such as when determining the best focus. The advantage of mode 1 is
that it moves the carriage more slowly so useful data can be acquired from a
much thinner strip. If scanning a previously plotted series which is done with
the command "plot scan series" then mode 1 is implicitly used.
Thermal
plot scan (series|<offset> <length> [<scan mode>])