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CHAPTER 2
– Measurement functions
Printing Plate
Beside energy and focus of the laser, dot gain is the most important information which
has to be checked in plate exposure. Special plate measuring instruments working
with video analysis have been developed for this application; for example TECHKON
SpectroPlate. Compared to densitometers and colorimeters they offer big advantages.
Nevertheless it is basically possible to make measurements with a densitometer on a
printing plate. In doing so one should regard the following: Variations in the coating of
the printing plates may result in strong influences on the measurements, especially in
the crucial range under 10 %. Variations of 0.02 D can cause errors up to 6 %.
The values measured with a densitometer do not correspond with the geometric dot
area, due to the fact that the densitometric measurement process is subject to optical
influences, which increase the measurement value. Therefore densitometers measure
always a higher value than video analysis devices. But the measurement value of the
densitometer can be taken as a reference value for the tonal value adjustment.
For the measurement of the zero point (1.), the solid patch (2.) and the screen patch
(3.) you should select areas on the printing plate which are located as close as possible
to each other.
1.
2.
3.
The measurement feature
Printing Plate
measurement allows reading values directly
on printing plates. The process is comparable to reading on printed paper.
Before taking a measurement it is important, that the rubber coating is washed off
the printing plate, because otherwise light gets lost and the measurement result will
be distorted. In addition a correction factor, the so-called Yule-Nielsen factor, can be
set according to the material characteristics of the printing plate. Usually the plate
manufacturer will furnish the information about the factor for the different plate types.
