Yokogawa 2-Wire Dual Channel Transmitter/Analyzer FLXA21 - Manual (Page 75)

<5. CALIBRATION OF pH/ORP>
5-1
IM 12A01A02-01E 5th Edition : Oct. 31, 2013-00
5. CALIBRATION OF pH/ORP
Before pH measurement, calibrate the pH sensor with the standard solution.
Before ORP measurement, check the electrode as a part of regular maintenance.
NOTE
A default is “10 min” for “Auto Return”. When maintenance like a calibration that may take much
time is performed, “60 min” or “Disable” is recommended to be selected. (Refer to the section
4.7.3.)
Calibration
Execute:
Calibration
HOLD
Temporary output
Setup:
Commissioning
Change language
Start Quick Setup
Execute & Setup Calibration pH
pH
ORP
Temperature Manual
Automatic
Sample
Temperature calibration
or
Only when “pH + ORP” is selected
on the Sensor setup screen
Figure 5.1 Calibration
The calibration items include pH, ORP, rH, and Temperature.
The item to be calibrated is determined according to the settings made in the Sensor setup and
Measurement setup in Commissioning.
Press to select Execute: Calibration, choose the item to be calibrated, configure the
calibration settings, then perform calibration.
NOTE
Note the following when performing calibration with buffer solutions.
1. Before starting a calibration, make sure the electrode system is properly cleaned and
the electrodes are fully functional. They must then be rinsed with clean water to avoid
contamination of the calibration solution(s).
2. Always use fresh buffer solution to avoid the risk of introducing errors from contaminated or
old solutions. Buffers supplied as liquids have a limited shelf life, especially alkaline buffers,
which absorb CO
2
from the air.
3. Yokogawa strongly recommends NIST/DIN 19266 buffer standards for the best accuracy
and buffer capacity. Commercially adjusted buffers (e.g., pH 7.00, 9.00 or 10.00) are a
compromise as a standard, and are often supplied without a temperature dependency
curve. Their stability will never be as good as NIST (JIS equivalent) solutions.
Always ensure that the sensors are properly conditioned, clean and filled with the correct
electrolyte solution (if appropriate) before starting a calibration. Refer to the sensor instructions
for details.
PH
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