YOKOGAWA EXA DO402G, Instruction Manual

Page: 61 / 82

IM 12J6B3-E-H
Calibration 6-1
6. CALIBRATION PROCEDURE
Calibration of the dissolved oxygen analyzer is performed in the following situations:
• When a new dissolved oxygen sensor is installed.
• When the membrane is replaced and/or the electrolyte solution is replaced
• When the sensor has been disassembled and reassembled for maintenance
• When the measuring error after cleaning exceeds the acceptable deviation from reference method
• When error message E12 or E16 indicates the need for maintenance
6-1. General
6-1-1. Calibration methods
There are three methods for calibration of the EXA dissolved-oxygen analyzer: air calibration, water
calibration and manual calibration.
Air calibration
This is the most common and easiest way to calibrate the analyzing system. The calibration is done in
AIR.CAL mode in maintenance level.
Water calibration
This is the traditional way to calibrate dissolved oxygen analyzers in laboratory environment. . Accurate
results can be obtained if the calibration is performed carefully. The water calibration may include a zero
calibration if so selected in service code 21. Normally only a zero check is performed without calibration,
since a good sensor has no zero signal.
Water calibration is not possible in salt water unless salinity compensation is activated in service code 04.
The calibration is done in
H2O.CAL mode in maintenance level
NOTE:
In normal industrial environment better results are obtained with air calibration, which is therefore the
recommended method.
Manual calibration
This is a calibration method whereby the sensor is not exposed to a calibration fluid, but is calibrated by
comparison with a reference method. This reference method is normally a laboratory analysis of the water
sample: either by Iodometric titration according ISO 5813 or an electrochemical method according ISO
5814.
The calibration is done in
MAN.CAL mode in maintenance level.