13
MODEL 226
SECTION 3.0
CALIBRATION
SECTION 3.0
CALIBRATION
SENSOR CALIBRATION.
After sensor and transmit-
ter/analyzer wiring is completed, electronic zero and
temperature slope adjustment should be performed
prior to field installation. The appropriate
analyzer/transmitter instruction manual (calibration
section) must be consulted in addition to the following
instructions.
NOTE
If you are using a Model 1054A Alkali Analyzer,
follow the calibration instruc
tions found in the
Model 1054AA instruction manual and ignore
the steps listed below. You must also enter a cell
constant of 1.25 into the analyzer before enter-
ing the lab-titrated alkali value.
The Model 226 sensor reading is affected by both the
immediate physical environment of the sensor, and to
a lesser extent, the conductivity range. Therefore, it is
very important to carefully follow the calibration proce-
dures as listed below, in order to obtain the most reli-
able, accurate reading. Read the following procedure
first before taking any action.
Materials needed:
Representative grab sample, large
glass beaker to fit sensor (suggested size: 3 liters),
large hot plate, thermometer, and stand and clamp
assembly to hold sensor in beaker away from the sides
and bottom.
1.
With the sensor wired to the transmitter/analyzer
with the full length of any extension cable, perform
an electronic zero as described in the appropriate
analyzer/transmitter instruction manual.
2.
Determine the normal temperature range of the
process. The minimum range for calibration pur-
poses is 10°C (18°F). With the sensor immersed in
the beaker, heat the sample to the lower tempera-
ture value. Shake the sensor to remove air bub-
bles trapped in the sensor hole.
3.
If you have a Model 1054/2054T Series analyzer,
perform a temperature standardization as
described in the analyzer instruction manual.
Otherwise, proceed to the next step.
4.
Keeping the “donut” portion of the sensor immersed in
the grab sample, clamp the sensor so that it is as far
away as possible from the sides and bottom of the
beaker, yet still in solution. You can use a clamp and
stand assembly. It is important to keep the sensor
away from the sides of the beaker because the cur-
rent and magnetic fields of the sensor are affected
by the physical environment of the sensor. For accu-
rate calibration, the sensor should be at least 2 inch-
es away from the walls and the bottom. If it is too
close, an error is induced due to the wall effects. You
can see this effect by watching the conductivity read-
ing change as you move the sensor hole close to the
sides of the beaker.
5.
With the sensor immersed in the solution at the
lower range temperature value, write down the con-
ductivity reading.
6.
Next, heat the solution and sensor to the upper
range temperature value. It should be at least 10°C
(18°F) higher than the lower range temperature
value. Make sure the sensor temperature is stable
here.
7.
Manually change the slope value on the
analyzer/transmitter until the conductivity reading
matches the conductivity reading you wrote down
in Step 4. The value will be between 1-4%.
8.
If you are using a 1054/2054T Series analyzer,
enter a cell constant of 1.25 as described in the
analyzer instruction manual.
9.
Install the sensor in the process and perform an on-
line standardization with a grab sample which has
been referenced to 25°C (77°F). This procedure is
described in the analyzer/ transmitter instruction
manual.
This standardization will set the value of the true cell con-
stant of the sensor. If you perform this on-line standardi-
zation at or very near the normal operating temperature
in a representative process stream, the loop error should
be only a few (2-3) µS/cm for low range (0-200 µS/cm)
measurements.
NOTE
The use of a decade box for calibrations is not
recommended due to the sensor geometry and
range.
