Yokogawa ISC450 4-Wire Analyzer for Inductive Conductivity - Manual (Page 44)

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IM 12D06D05-01E
6. CALIBRATION
6-1. Before calibration
1. When is calibration necessary?
Calibration of con duc tiv i ty in stru ments is not
nor mal ly nec es sary as the con duc tiv i ty cells
are man u fac tured to close tol er anc es and do
not al ter in use.
If the cell has severe fouling or been sub ject to
abrasion (possibly during cleaning) it may be
necessary to calibrate.
Since the ISC450G/ISC40 inductive con duc-
tiv i ty system measures the conductivity of the
“liq uid winding” through the doughnut, part of
this “measuring cell” is outside the dough nut.
If there is little space between dough nut and
process piping, calibration with a sam ple of the
process fluid is necessary to en sure ac cu rate
measurement.
2. How is calibration done?
Calibration is carried out by measuring a
so lu tion which has known conductivity and
ad just ing the instrument to show the cor rect
conductivity value.
The calibration can be achieved using one of
two methods:
1) A calibration solution can be prepared in
the laboratory. A salt solution is prepared
with a known precise concentration.
Thetem per a ture is stabilized to the ref-
er ence tem per a ture of the instrument
(usu al ly 25 °C). The actual conductivity
value of the solution is taken from tables.
To calibrate the in stru ment, the sensor is
removed and sus pend ed in the solution,
the conductivity val ue from the tables is
then entered and the cal i bra tion routine
completed.
Make sure the sensor does not touch the
sides of the container, refer to Figure 6-1.
2) Alternatively the instrument can be cal i brat-
ed using the process solution meas ured
with a standard instrument. Care must be
taken to make the measurement at the
ref er ence tem per a ture since differences in
the type of tem per a ture compensation of
the instruments may cause an error.With
this method the sensor is not removed
from the process. This method is the
most convenient method of calibrating
the ISC450G converter. Since the sensor
is im mersed in the process, errors
caused by in stal la tion characteristics are
compensated for.
Note! The standard instrument used as
ref er ence method must be ac curate.
Yokogawa recommends that the Model
SC72 personal conductivity meter be
used for this purpose.
X = MIN 25 mm
X X
X
igure 6-1. Sensor in calibration solution