FIFTH CANADIAN CONFERENCE ON NONDESTRUCTIVE ... - IAEA

TESTING (Continued)
- 165 -
Anything can be monitored and placed on a chart. However, not everything
need be tested all of the tine. For instance, unless there is some indication
of a problem then line voltage might only be checked annually. Transport
rates in inches or centimeter per minute might be measured monthly.
Replenishment/regeneration rates should be measured weekly. Temperature is
often monitored daily. Chemical tests are difficult to perform, but could
include bromide, pH, hydroquinone, and archival quality testing performed by
a film manufacturer. Clearing time tests, silver content tests, and specific
gravity tests could be performed periodically in-house. However, the sum
total of the process is the effect of the chemicals, controlled by the
electromechanics, on a controlled exposure in a controlled film emulsion.
This then is sensitometric quality control and is the best test and the most
common test.
SENSITOMETRIC QUALITY CONTROL
Ferdinand Huerter and Vero Driffield in the late 1890's were experimenting as
amateur photographers with different photographic emulsions for scientific
recording of events. They found different emulsion formulas produced different
results so they set out to characterize how a certain film emulsion
responds to a controlled exposure and controlled development. By giving the
candidate emulsion a controlled exposure and controlled processing they could
see how it compared to other emulsions. Thus, there are three components to
this test: film, exposure, and processing (development). If any two components
or variables are held constant, the third may be tested. Sensitoroetric
quality control is a measure of the sum total of the image forming process.
We borrow from the past to see us into the future. But, do not confuse
sensitometry with densitometry which is the measurement of a density in a
pentrameter to meet a work specification.
In sensitometry there are four measurements:
o D-Max: Maximum density for maximum exposure
o Contrast: Difference between two density levels
o Speed: The amount of exposure to produce a density of 2.00
o D-Min: Minimum density for minimum exposure
Base plus fog (B+F) is a measurement of the inherent fog, base, and tint
values combined and occur prior to an exposure. B+F is not a sensitometric
value.