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Input Calibration
138 UDA2182 Universal Dual Analyzer Product Manual January 2009
8.3 pH/ORP and Conductivity Overview
pH/ORP Calibration
Calibration of pH or ORP measuring instruments is necessary because similar electrodes
may produce slightly different potentials in the same solution, requiring a corrective
adjustment at the measuring instrument. Also, electrode outputs change over a period of
time, making periodic recalibration necessary for best performance. Determine
recalibration intervals based on operating experience.
Conductivity
Each type of cell has an associated cell constant entered during Configuration Setup. (See
Section 6.6) This number is part of the cell model number. However, for greater precision,
every Honeywell cell is individually tested at the factory, and a calibration factor unique to
that cell is determined. The cal factor for a cell can be found on the plastic tag hanging
from the cell lead wires. Instructions for entering this cell cal factor are in Section 6.6. The
UDA automatically uploads the Cal Factor from Honeywell cells with EEPROM. This
value is displayed in the “Setup” menu.
For some conductivity applications even greater accuracy is required. For those
applications it is possible to perform a calibration trim procedure. The Analyzer’s reading
can be adjusted while the associated cell is measuring a reference solution of known
conductivity, as described in Section 8.7. The same procedure can be used to adjust the
Analyzer’s reading while the cell is in the process, if a reference instrument is used to
determine the conductivity of the process. In this case the process fluid becomes the
“reference solution”.
Calibration trim is recommended for acid concentration applications above 5%.
Calibration trim can be reset as described in Section 8.7.
For accurate measurement of total dissolved solids (TDS) a conversion factor is entered
for each cell as described in Section 6.6.
ATTENTION
Any time a unit reset is performed; the TDS Value will be reset to 1.0. Calibration trim and cal
factor will be reset for cells.