Hach si792 D series, User Manual

Page: 74 / 96

Calibration
72
8.1.1 Zero calibration
Perform a zero calibration as the first point whenever a 2-point
calibration is required.
Note: The DO sensor models SE 704, SE 705 and InPro6000 have a
very low zero current. Therefore a zero calibration is only
recommended for measurement of oxygen traces.
Allow the sensor to stabilize in the calibration medium for at least 10 to
30 minutes (InPro6900 at least 60 minutes). A drift check will not be
made. The zero current of a properly functioning sensor is notably less
than 0.5% of the current in air.
The display will not change until an input current is entered for the zero
point. When measuring in an oxygen-free medium, the displayed
current can be taken directly.
Complete the following steps to set the zero point.
1.
Press
CAL
, enter passcode: 1001,
ENTER
. The main display will
show CAL ZRO and then the entered value (in nA) for the zero
point. The secondary display shows the measured current.
2.
Place the sensor in an oxygen-free medium.
3.
Press
ENTER
to accept the value or correct the value and then
press
ENTER
.
4.
The slope of the sensor will be shown in the main display. The new
zero point will be shown in the secondary display. Press
ENTER
to
end the calibration.
5.
Return the sensor to the process. The oxygen value will be shown in
the main display alternately with Hold. Press
ENTER
to return to the
measure mode.
8.1.2 DO calibration (default)
Make sure that DO is selected in the configuration menu (
Table 9 on
page 36
). For a 2-point calibration, calibrate the zero point first