In-Situ TROLL 9500 Operators Manual - Manual (Page 88)

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TROLL 9500 Operator’s Manual 0095110 rev. 007 01/09
depleted solution such as sodium sulfite or nitrogen-saturated
water. A 2-point calibration is recommended
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Nominal vs. Stable
To shorten the calibration time, you have the option to accept the
calibration when “Nominal” stability is achieved. If the early value is
accepted, the calibration point will be designated “USER SET” in the
calibration report. If the calibration report indicates that calibration
was performed through to stability then the instrument will operate as
intended by In-Situ’s quality standards.
CALIBRATION SOLUTIONS & EQUIPMENT
100% D.O. calibrations may be performed in water saturated with air,
or in air saturated with water. Deionized water is available from In-Situ
Inc., but any clean water may be used. In-Situ’s bubbler calibration kit
is designed for an efficient water calibration.
An oxygen-depleted solution is used to calibrate the 0% D.O. Sodium
sulfite is available from In-Situ Inc. For a cleaner calibration, nitrogen-
saturated water may be used.
RECOMMENDED CALIBRATION FREQUENCY
Your own experience is the best guide to how often the polarographic
D.O. sensor will benefit from recalibration under conditions of normal
usage. Refer to the general guidelines under “How Often to Calibrate”
in Section 10, and the tech note on “Instrument Calibration.”
Until a new polarographic sensor has been thoroughly conditioned, it
may require more frequent calibration. In the absence of other indica-
tions, a calibration should be performed every 2-4 weeks.
In addition, the polarographic D.O. sensor should be conditioned for
2-4 hours and recalibrated in the following circumstances:
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which the sensor was last calibrated.
DISSOLVED OXYGEN CALIBRATION TIPS
The following discussion may help you to obtain the best results from
the polarographic D.O. calibration.
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100% D.O. calibration:
in air (saturated with water). This is the condition during a Quick
Cal in the inverted Cal Cup with the sensor membrane exposed
to air, temperature sensor submerged, and Cal Cup vented to
the atmosphere.
in water (saturated with air). In-Situ’s bubbler calibration kit
provides everything needed to create a vigorous bubbling action
to insure air-saturated water. The Cal Cup is not used.
Since dissolved oxygen measurements are typically made in water,
calibrating in water will often yield better results. When calibrated in
air, the membrane’s behavior in water must be estimated.
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temperature. Ideally, it should be done in an area protected from
direct sunlight and away from ventilation ducts.
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sure to note the membrane thickness before starting the calibra-
TION
DISSOLVED OXYGEN QUICK CAL
The procedure to Quick Cal the polarographic D.O. sensor, along with
other Basic sensors, is in Section 3, Getting Started. This is a single-
point 100% calibration in air (saturated with water).
The following traditional calibration is recommended for use when
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temperature and pressure,
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TRADITIONAL DISSOLVED OXYGEN CALIBRATION PROCEDURE
You may select a 1-point or a 2-point calibration. The first point (100%
saturation) may be taken in air or in water.
Prepare the MP TROLL 9500 for water or air calibration as described
in Steps 1-6 on the following page.
SECTION 13: DISSOLVED OXYGEN—POLAROGRAPHIC
I did a Quick Cal. Why should I recalibrate D.O.?
The D.O. Quick Cal, especially if done through to stability,
can provide accurate measurement results. However, some
procedures require a look-up table for the stimulus at a given
temperature and pressure. This can be done in the traditional
D.O. calibration. Also, better measurement results will be
obtained when the 100% calibration is done in water saturated
with air. This procedure is not provided for in Quick Cal. In addi-
tion, the traditional calibration provides for a 0% (0 ppm, 0 mg/L)
calibration, which is recommended when measuring very low
D.O. values.
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