FIFTH CANADIAN CONFERENCE ON NONDESTRUCTIVE ... - IAEA

INTRODUCTION (Continued)
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Processing, being a chemical process, is controlled by elements of time,
temperature, and activity. "Time" is the immersion time the film is in the
chemical and is controlled by a human in manual processing or transport speed
in the transport system of an automatic processor. Temperature control is
very specific and is related to the time factor and the activity factor. The
shorter the time for a given developer activity level or quality, the higher
the temperature required to produce a certain density. Thus, there is a
balance between time and temperature based on a given chemical activity.
This balance allows longer times at lower temperatures or shorter times and
higher temperatures. However, these relationships only work for a givtn
activity. This means the developer must be of a certain quality as a result
of correct mixing, starter solution, and an accurate replenishment/regeneration
rate. Thus, to control processing quality there are three test approaches:
TESTING
o Electromechanical
o Chemical
o Sensitometric
Testing is performed periodically to determine if the process is in control.
Walter A. Shewhart in the early 1940's created the "Trend Chart" which had two
goals: indicate a problem requiring a decision or action, and help indicate
the right decision. He stated that if we control the major variables we do
not have to worry about the minor variables. In radiographie processing there
is time, temperature, and activity or three major variables. Shewhart states
that a trend chart has upper and lower control limits to either side of a goal
or aim value. If there is a large spike or fall-off from the average track of
the chart this is due solely to one of the major variables being out of
mni-rol. Two other interesting facts about trend charts:
o The uncontrolled variables will prevent a straight,
line track. There should be some random fluctuation.
o Although the trend chart demonstrates a problem, the
goal of a quality control program is to never have a
problem.