Yokogawa DO202 2-Wire Dissolved Oxygen Analyzer - Manual (Page 54)

IM 12J05C01-01E
Calibration Procedure 6-3
6-3-3. Procedure for water calibration
NO
SC21=0
NO
SC21=1
NO
NO YES
NO YES
NO
NO YES
YES
Press the MODE key. CALIB appears in the display, and the
YES/NO key prompt flags flash. Press YES.
NO YES
NO YES YES NO
After briefly displaying WAIT,
the display returns to the
normal readout.
YES
Sensor can be returned
to process water.
Press YES for single point
adjustment.
YES
NO
NO YES
NO
NO
YES
YES
Go to
6-4-2
Go to
6-4-3
NO YES
The instruments
waits for the
reading to
stabilise.
(The display
flashes). When
reading Is stable,
the CAL END
message
appears.
ENT
FAIL TEMP.MAN
YES NO
ENT
NO MODE YES
MODE
%sat
ppb
CAL
DISPLAY
ppm
HOLD
OUTPUT
SET HOLD
SERVICE
YES NO
YES YES
YES YES
YES YES
to *1
NO
Note: To start calibration with a zero solution
(zero-dissolved-oxygen solution.)
from *1 NO
NO to *1
6-3. Calibration procedure using water calibra-
tion method
6-3-1. Preparation
Move the sensor to a maintenance site and wash
off any dirt on the membrane. Lightly wipe off any
remaining water from the membrane with a soft tissue.
Prepare the necessary equipment and reagents to be
used for the span and (if required) zero calibration.
Equipment for span calibration includes:
• Beaker or bucket
• Magnetic stirrer or other means of agitating the water
• Demineralized water or salty process water if
salinity compensation is activated
• Air supply pump (aquarium pump)
• Glass diffuser to generate small air bubbles
Note: It takes 15 to 30 minutes of aeration before
it can be assumed that the water is fully
saturated with air.
Reagent for zero calibration:
• Sodium sulfite
• demineralized water
The zero oxygen solution contains 20- 30 grams of
sodium sulfite per liter.
6-3-2. Calibration operation
(water calibration method)
If both zero and span calibration are used, it is bet-
ter to start with span calibration in spite of normal
calibration sequence with analog instrumentation.
Otherwise the sensor must be rinsed off carefully to
prevent ingress of oxygen absorbing sulfite in the
aerated water.
Note: Zero calibration in the sodium sulfite solution
takes a long time. Even after CAL.END
prompt it is necessary to wait 40-50 minutes
before zero adjustment can be made.
Otherwise calibration errors are introduced in
the measurement. It is recommended not to
do a zero calibration, but a zero check only.
A good clean sensor does not have a zero
current and does not require zero calibration.
If the sensor has a substantial zero current,
the sensor has to be disassembled, cleaned
and filled with fresh electrolyte solution and a
new membrane has to be fitted.
Calibration may take longer than 10 minutes.
Before starting the calibration procedure,
check the setting of Auto Return (*RET.) in
Service Code 50. It is recommended to set
the Auto Return to “0” (No return to meas.
from HOLD). After the calibration procedure
has been completed, set the Auto Return to
the desired setting in Service Code 50.