58
SECTION 5,
continued
5.5
Measuring Dissolved Oxygen
5.5.1
General Probe Operation
Follow the procedures presented below to obtain maximum
performance and accuracy from your sens
ion
156 DO system:
•
Use the DO probe for aqueous applications only.
•
Take extra care when handling and storing the oxygen
membrane module cap.
•
Do not allow the DO probe’s sensing area (cap reservoir) to
dry out.
•
Perform the calibration procedure at the beginning of each
day for maximum performance. Recalibrate the DO probe
every two hours for maximum accuracy.
•
The sample must have a high flow rate or must be stirred
rapidly to obtain accurate results.
•
Be sure any air bubbles trapped on the probe tip are dislodged
before taking a reading.
•
It is important to have the DO probe at a uniform
temperature. Do not touch the metallic button on the side of
the probe when holding it. The metallic button is a thermistor
that senses sample temperature. An inaccurate measurement
will result if the temperature of the thermistor is not the same
as the membrane end of the probe.
5.5.2
Dissolved Oxygen Measurement
After the probe is properly stabilized, chemically zeroed (only
necessary for measurements below 1 mg/L where high accuracy
is required), and calibrated, take measurements as follows:
1. Add the weight assembly to the probe if required (3 or 15 m
cable versions only).
2. If the sample salinity has been measured using a conductivity
probe, enter the value in Setup 7. (You can also update this
setup from Salinity Reading mode by pressing the up arrow.
See Section 4.6 on page 44.)
