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Control Chart Interpretation
Film Process Records

Photography (Advanced) - Advanced manual for photography and other graphic techniques
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Figure  2-15.—Control  chart  interpretation. a random pattern includes a run, the process may need 4.  Ensure  the  processing  temperature,  agitation, corrective action. and times are correct. Correct  Diagnosis 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 discrepancy. 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 correct it: 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 the following: 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 replaced. 3. Recheck the calculations and the plotting of values. Maintain a continuous record of the process. 2-29







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