Yokogawa DO402 Dissolved Oxygen Analyzer - Manual (Page 67)

IM 12J05D02-01E
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 measuring error after cleaning exceeds the acceptable deviation from reference method
• When error message E12 or E16 indicates the need for maintenance
Note:
When a new sensor is installed, when the membrane is replaced, and/or the electrolyte solution is
replaced, it may take some time for the electrodes to stabilize due to the initial electrolysis. In particular,
a zero calibration should be performed after the electrodes are exposed to the air or immersed in sam-
ple water for about half a day. When the sensor cable terminals 13 and 15 are shorted together before
installation, the time for the zero point to stabilize can be reduced.
Note:
It may take a long time for the electrodes to stabilize in the first electrolysis just after installing the
DO30G sensor or other galvanic sensors and polarographic sensors, or after replacing the membrane
or electrolyte solution. The zero calibration in particular should be carried out after leaving the sensor
operating in air or measurement liquid for about half a day. The time for stabilizing the zero point can be
reduced by shorting the terminals 13 and 15 of the sensor cable before installation.
6-1. General
6-1-1. Calibration methods
There are three methods for calibration of the EXA dissolved-oxygen analyzer: air calibration, water cali-
bration 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.
Always select 1 in service code 21 for the DO70G optical dissolved oxygen sensor.
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.
Note:
Calibration must be carried out after changing the manual pressure setting (see service code 51).
When the manual pressure is enabled, air and water calibrations are made based on the specified pres-
sure. M.PR.ON YES/NO is displayed before the calibration to confirm whether the calibration will be
made based on the pressure.