Calibration And Maintenance - Emerson Rosemount 3900 Quick Start Manual

Quick Start Guide
4

Calibration and maintenance

Calibrate pH/ORP sensors at start-up to obtain the best accuracy.
Consult the appropriate Rosemount liquid analysis transmitter
manual for specific calibration and standard procedures or see
Calibrate a pH sensor with two buffer
sensor, or
sensor
4.1 Calibrate a pH sensor with two buffer solutions
A two-point buffer calibration is the only way to ensure that a
pH sensor is providing accurate measurements. During a two-point
calibration, the transmitter calculates new values for slope (mV/pH)
and zero offset (mV) based on the mV response of the sensor when it
is in the pH standard solutions.
Procedure
1. Immerse the sensor in the first buffer solution. Allow the
sensor to adjust to the buffer temperature (to avoid errors due
to temperature differences between the buffer solution and
sensor temperature) and wait for readings to stabilize.
2. Once the transmitter has acknowledged the first buffer, rinse
the buffer solution off the sensor by pouring a small amount
of the second buffer solution over the tip of the sensor.
3. Repeat
Once the transmitter has acknowledged both buffer solutions, a
sensor slope (mV/pH) is established.
4.2 Standardize pH sensor
For maximum accuracy, you can standardize the sensor in-line or
with a process grab sample after performing a buffer calibration
and conditioning the sensor to the process. Standardization
accounts for the sensor junction potential and other interferences.
Standardization does not change the sensor's slope, but simply
adjusts the transmitter's reading to match that of a known process
pH.
Procedure
1. While obtaining a process solution sample, record the pH
value that is shown on the transmitter display.
Emerson recommends taking the sample close to the sensor.
22
Calibrate Rosemount oxidation reduction potential (ORP)
for recommended procedures.
Step 1 using the second buffer solution.
solutions, Standardize pH
May 2023
Emerson.com