Emerson Rosemount 228, Reference Manual, Page: 30 / 44

If wall effects are absent in the process installation, use a sufficiently large container
for calibration to ensure that wall effects are absent. To check for wall effects, fill the
container with solution and place the sensor in the center, submerged at least 3/4 of
the way up the stem. Note the reading. Then move the sensor small distances from
the center and note the reading in each position. The readings should not change.
If wall effects are present, be sure the vessel used for calibration has exactly the
same dimensions as the process piping. Also ensure that the orientation of the
sensor with respect to the piping is exactly the same in the process and calibration
vessels. See
Figure 4-2 .
Calibration installation orientation Figure 4-2:
3. Rinse the sensor with water.
4. Immerse the rinsed sensor in the standard solution.
Use a good quality calibrated thermometer to measure the temperature of the
standard solution. The thermometer error should be less than ±1 °C. Allow adequate
time for the solution and sensor to reach thermal equilibrium. If the sensor is being
calibrated in an open beaker, keep the thermometer far enough away from the
sensor so it does not introduce wall effects. If the sensor is being calibrated in a pipe
tee or similar vessel, it is impractical to place the thermometer in the standard
solution. Instead, put the thermometer in a beaker of water placed next to the
callibration vessel. Let both come to thermal equilibrium with the ambient air before
continuing calibration. See
Figure 4-3 .
Calibration
24 Reference Manual