Description:

The command "plot phase" sets a particular pattern in the scorr table and writes a 3.9 inch wide strip. The scorr table is then set to zero and another 3.9 inch wide strip is written. Scanning both of these using the focus laser allows the focus laser offset from the center of the swath to be determined. This value is converted to a starting point sub scan shift and put into the head NVS parameter "fsphase". This number should be close to zero or close to the number of channels i.e. a small positive or negative number modulo the number of channels. These two strips are also used to estimate the scale factor relating a percent change in scorr value to a density on the plate. This number should be between 200 and 300 for a Kodak plate and is stored in the head NVS parameter "scanscale". The command "plot phase" also determines the initial slope and updates the NVS parameter "bmslope" for the currently selected media (ie. the current active hdm NVS parameters). The NVS parameter "bmcurve" is set to zero since a curve of any shape is handled by the scorr table.

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. This provides 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.

Applies To:

• Thermal

Syntax:

Notes:

See Also:

• Command: plot
• Command: plot flatten
• Command: plot scan
• NVS: hdm bmcurve
• NVS: hdm bmslope
• NVS: head fsphase
• NVS: head scands
• NVS: head scanlpos
• NVS: head scanscale
• NVS: sys newd
• NVS: sys scanntu