In-Situ TROLL 9500 Operators Manual - Manual (Page 129)

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TROLL 9500 Operator’s Manual 0095110 rev. 007 01/09
Q:
A:
Why do I need to calibrate the turbidity sensor if it
has been calibrated in the factory?
A new turbidity sensor is ready to measure turbidity with
reference to suspended polymer standards. If you prefer
to reference turbidity measurements to Formazin rather
than polymer, a field calibration with Formazin should be
performed.
After cleaning the sensor, readings should be checked
with standards and a field calibration performed if
necessary.
MANUAL WIPE
To wipe the turbidity sensor optics manually:
1. With the wiper installed in port 3, connect the MP TROLL 9500 to a
PC and establish a connection in Win-Situ 4 or Pocket-Situ 4.
2. Select the Wiper in the Navigation tree.
3. Click Wipe. The wiper will pass once over the turbidity sensor
optics and return to its home position.
WIPER GUIDELINES AND PRECAUTIONS
s
Section 3, Getting Started), steps should be taken to insure the
wiper pad material does not absorb the Quick Cal solution. There
are two ways to do this.
– Remove the wiper head before doing the Quick Cal. Refer to
Wiper Maintenance guidelines later in this section for instruc-
tions on removing the wiper head.
– Alternatively, soak the front end of the instrument in plain water
before calibrating to allow the wiping pad to absorb sufficient
water to prevent its absorbing any Quick Cal solution.
s
ment is software-controlled.
s
is effectively cleaning the sapphire windows of the turbidity sensor
during movement. Refer to Wiper Maintenance guidelines later in
this section.
s
Maintenance guidelines later in this section.
s
to see that the RDO adapter cable is out of the way of wiper move-
ment.
CALIBRATION
FACTORY CALIBRATION
The turbidity sensor has been factory-calibrated to achieve a sensor
accuracy of ± 5% or 2 NTU (whichever is greater). The sensor is
calibrated over its full range, 0 to 2000 NTU, using polymer standards.
The resulting calibration coefficients are written to the sensor memory,
where they are stored permanently. They may be overlaid by perform-
ing a field calibration as described below, or may be recalled from the
sensor memory at any time.
The MP TROLL 9500’s turbidity sensor is ready to measure turbidity
without any user intervention. It is advisable to take a turbidity reading
first in your own calibration solution(s) as a check to ensure the ac-
curacy is within your operational standards and requirements. If this
result is satisfactory, a field calibration is not required.
FIELD CALIBRATION
Field calibration (or “user calibration”) is an overlay function that is
applied after the factory calibration math is done. The factory calibra-
tion applies across the entire range of NTU, and can be altered in the
field with a 1 to 4 point calibration procedure as described below to
compensate for effects of sensor fouling and other factors. You may
wish to perform a field calibration with standards other than polymer
(i.e., Formazin).
For best results, calibrate as close to field temperature as possible.
CALIBRATION SOLUTIONS
A nephelometer such as the In-Situ turbidity sensor should be
calibrated using standard reference suspensions having reproducible
light-scattering properties. The sensor has been factory-calibrated
with polymer suspensions, and the resulting calibration coefficients
take into account the light-scattering properties of the suspensions
and the sensor optics.
SECTION 18: TURBIDITY
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3