Chapter 3 Calibration; Sensor Calibration; Calibrating Against A Standard Solution - Emerson Rosemount 225 Reference Manual

Reference Manual
00809-0100-3225
3 Calibration
3.1

Sensor calibration

The nominal cell constant of the Rosemount 225 sensor is 2.7/cm. The error in cell
constant is about ±10%, so conductivity readings made the using the nominal cell constant
will have an error of at least ±10%. Wall effects,as shown in
error greater.
There are two basic ways to calibrate a toroidal sensor: against a standard solution or
against a referee meter and sensor. A referee meter and sensor is an instrument that has
been previously calibrated and is known to be accurate and reliable. The referee
instrument can be used to perform either an in-process or a grab sample calibration.
Regardless of the calbiration method used, the connected transmitter automatically
calculates the cell constant once the known conductivity is entered.
For more detailed information on calibration methods, please reference application data
sheet ADS-43-025 available on the
Figure 3-1: Measured Conductivity as a Function of Clearance between Sensor and
Walls
3.2

Calibrating against a Standard Solution

Calibration against a standard solution requires removing the sensor from process piping.
This calibration method is practical only if wall effects are absent or if the sensor can be
calibrated in a container identical to the process piping. Ideally, the conductivity of the
standard used should be close to the middle of the range that the sensor will be used in.
Generally, toroidal conductivity sensors have good linearity, and so standards greater than
5000 µS/cm at 77 °F (25 °C) may also be used.
Rosemount 225 Sensors
Figure
Emerson Liquid Analysis
Calibration
August 2018
3-1, will likely make the
website.
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