In-Situ TROLL 9500 Operators Manual - Manual (Page 130)

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TROLL 9500 Operator’s Manual 0095110 rev. 007 01/09
Polymer-based standards are submicron, non-surface charged, solid
spheres in matrixes of ultrapure water in homogeneous suspension;
this homogeneity allows linear dilutions. EPA approved the polymer
suspensions in 1984 as a calibration standard for turbidimeters.
Polymer suspensions are very stable, can withstand temperature
extremes, and have excellent lot-to-lot precision. A range of polymer
suspensions are available individually from In-Situ Inc. for calibrating
any expected turbidity range. They can be diluted with turbidity-free
water to achieve other NTU values (but see the cautions below).
Avoid vigorous mixing or agitation, which will create air bubbles and
lower the accuracy of the standards. It is advantageous to calibrate a
nephelometric turbidimeter with a standard that most closely matches
the size of the particulates you will be measuring.
Calibrating with Other Solutions
Formazin: If you wish to recalibrate with Formazin, keep these points
in mind.
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utes before use.
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Diluting Polymer Suspensions: If you dilute polymer suspensions,
keep these points in mind:
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“primary standards”, they become “secondary standards.”
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suspension of particles may be lost.
RECOMMENDED CALIBRATION FREQUENCY
Your own experience is the best guide to how often the turbidity sen-
sor will benefit from recalibration. The need for recalibration depends
on the condition of the optical windows, which in turn depends on
the environment. In a biologically active environment, cleaning and
calibration will be required more often. Periodic checks in calibration
solutions of known turbidity can be beneficial in indicating how well
the sensor is holding its calibration.
A field calibration is recommended
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than polymer.
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results.
CHANGES
TURBIDITY CALIBRATION PROCEDURE
You will need:
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unused sensor ports.
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be installed when turbidity is measured.
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bration solution.
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to calibrate. Several ranges from Very Low to Full are suggested in
the Calibration Wizard.
TIP: A 1-point to 4-point field calibration may be carried out
in any range. When performing a multi-point calibration,
begin with 0 NTU solution. For best measurement precision
the highest NTU value should exceed the readings you expect in the
field.
1. Rinse the front end of the MP TROLL 9500 with clean water. Shake
well to remove the rinse water; dry external surfaces (not the opti-
cal windows) with a clean tissue.
2. Pour the selected calibration standard into the beaker and insert
the MP TROLL 9500 into the solution.
The windows of the turbidity sensor should be immersed at least
¼” (a quarter of an inch) deep in the solution. If no wiper is present,
gently agitate the instrument to dispel any air bubbles.
SECTION 18: TURBIDITY