5.
Surveillance of the reference and working groups of cells will be
maintained.
Surveillance will consist of monthly comparisons of the
reference and working cells and plotting the computed value of each cell and
the mean of the groups.
a. The following computations and graphs are required:
(1) The value of each cell and the mean of the working group based on
the mean of the reference group (compute and graph).
(2) The value of each cell in the reference group based on the mean
of the reference group (compute and graph).
(3) Left-right component (compute only).
b. Upon receipt of the calibration report from the APSL, the ACF will
construct graphs similar to Figure 3-7 and should be in accordance with 1
through 3 below:
(1) Enter the calibration report value for each of the cells and the
mean of each group at the appropriate point on the graphs at time zero and
enter the date at the bottom of the graph.
(2) Enter the upper and lower control limits.
These limits will be
supplied by the APSL in the calibration report.
(3) At monthly intervals following calibration, compare the reference
and working cells and compute the value of all cells in terms of the mean of
the reference group. Enter the computed data in the graphs.
c. Surveillance plots are considered within control if plotted data is
within upper and lower control limits.
d. Out-of-control conditions and actions will be determined in the
following manner:
(1) The average left-right component (residual EMF) is 0.10 V for
systems used in the ACFs.
Any computed left-right component exceeding
0.30 V indicates a requirement for determining system errors (sources of
thermal EMF, cell instability, potentiometer errors, etc.).
In situations
where left-right component computations exceed 0.30 V and the sources of
errors cannot be traced locally, guidance should be requested from the APSL.
(2) Control limits on the surveillance charts signal out-of-control
conditions for the cell.
Individual out-of-control cells in the working
group should not be used as standards for calibration; however, surveillance
should continue.
In some cases, the condition will be temporary and will
return to an in-control condition.
In the event of an out-of-control
working group mean, request guidance from the APSL.
The reference group
mean will track a straight line by definition. In the event as many as two
reference group cells drift out-of-control, request guidance from the APSL.
61
Previous Page
