Hanna Instruments HI 4421 - Manual (Page 38)

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Make sure the instrument has been calibrated before taking DO measurements.
DIRECT MEASUREMENT
To measure the DO of a sample using the Direct reading mode:
• Press
and then to select DO measure mode.
• Select the Direct reading mode (see DO Setup ).
• Submerge the DO probe and tap it repeatedly to remove any
air bubbles that may be trapped inside the sleeve. Allow time
for the reading to stabilize.
• The measured DO value will be displayed together with the
temperature and pressure values.
Notes: • For accurate DO measurements, a water movement of
0.3 m/s is required. This is to ensure that the oxygen-
depleted membrane surface is constantly replenished.
A moving stream will provide adequate circulation.
• If the reading is out of range, “-----” will be displayed.
DIRECT/AUTOHOLD MEASUREMENT
To measure DO of a sample using the Direct/AutoHold reading mode:
• Select the Direct/AutoHold reading mode (see
DO Setup ).
• If pressing , the “AutoHold” indicator will start blink-
ing on the display until the stability criterion is reached. The DO
value will be frozen on the display, along with “AutoHold”
indicator.
• To return to normal measure mode press .
DO MEASUREMENT DO MEASUREMENT DO MEASUREMENT DO MEASUREMENT DO MEASUREMENT