Figure 2-15.Control chart interpretation.
a random pattern includes a run, the process may need
4. Ensure the processing temperature, agitation,
and times are correct.
Sometimes two or more things may go wrong
with a process at the same time and it is not clear
which of several probable causes is resulting in trend,
jump, or run patterns. In this case, each of the
probable causes must be investigated until the cause(s)
of the undesirable condition is/are found and
eliminated. When there is more than one probable
cause, you should start with the easiest one to correct,
or the one that is most likely to occur.
5. Review the chemical mixing and/or
replenishment records to determine whether there is a
When there is a sudden jump in the plot, look for
factors that occur rapidly, such as changes in
chemicals, temperatures machine speed, and so on.
When a plot falls outside of the upper- or
lower-control limits, follow the steps given here, in
the order of precedence, until you find the cause and
6. Prove or disprove the value of the
questionable out-of-control plot by immediately
running another control strip or taking another pH or
specific gravity reading, as appropriate. This should
eliminate the possibility of one improperly exposed,
processed, or handled strip from indicating a problem
in an otherwise normal process. When the values of
this second reading are within limits, you can assume
that the first or out-of-control value was the result of
irregular or random conditions, and resume
processing. On the other hand, when the second
reading also gives an out-of-control value, stop
processing production work until the problem has
been found and corrected.
1. Check the appropriate instrument, such as the
sensitometer, densitometer, pH meter, and hydrometer,
to be sure it is calibrated and being used correctly.
Monitoring black-and-white film processing is not
difficult. A good-quality assurance program that relies
heavily upon process monitoring can enable you to do
Detect problems before they become serious.
2. Reread the sensi-strip or control strip densities
or chemical sample to eliminate reading error as a
cause of out-of-control plots.
Test processing solutions and evaluate their
usefulness to determine when they need to be
3. Recheck the calculations and the plotting of
Maintain a continuous record of the process.