52
SECTION 5,
continued
5.4
Dissolved Oxygen Calibration
The sens
ion
156 Dissolved Oxygen meter must be calibrated
prior to use. Prior to calibration, the probe must be prepared and
stabilized. For measurements below 1 mg/L DO, the probe should
be zeroed prior to calibration. See Section 5.4.2 Zeroing the
Probe.
The calibration may be performed in three ways:
•
Calibration may be performed in a water-saturated air
environment. See Section 5.4.3.
OR
•
Calibration may be performed using a water sample that has a
known dissolved oxygen concentration in mg/L. The sample
concentration is determined by another technique such as a
Winkler titration. See Section 5.4.4.
OR
•
Calibration may be performed by setting a water sample to
100% saturation. See Section 5.4.5.
5.4.1
Probe Polarization
Hach dissolved oxygen probes are continuously polarized when
they are connected to the instrument. A steady reading will not be
seen for 30–50 minutes when the probe electrolyte is new or
when the probe has been unplugged for more than one hour.
Interrupted connections of less than one hour will require 5–25
minutes before a stable reading is observed.
With the probe in the calibration and storage chamber, observe
the mg/L dissolved oxygen concentration after the probe has been
polarized for the appropriate period of time. Calibration may be
performed when the display is stable for several minutes.
