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TROLL
9500
Operator’s Manual
0095110 rev. 007 01/09
be detected. The plate is then pulled up until it is visible again. The
average of the two depths provides an estimate of water clarity or
transparency.
Modern turbidimeters measure the loss in intensity of a light beam
as it passes through a solution containing suspended and dissolved
particles that are large enough to scatter the light. The method is
based upon a comparison of the intensity of light scattered by the
sample with the intensity of light scattered by a standard reference
suspension. The
nephelometer
is a particular type of turbidimeter
THATMEASURESTHEINTENSITYOFLIGHTSCATTEREDATRIGHTANGLES½ TO
the incident light. This lessens the difficulty of differentiating small
changes against a large background. Standards for turbidity-measure-
ment instruments specify the light source, angle, wavelength, beam
width, and sample suspensions, among other factors. Many of today’s
commonly accepted procedures (e.g., Standard Methods, EPA, and
ISO) apply to laboratory bench-top instruments.
THE TURBIDITY SENSOR
The optional turbidity sensor of the Multi-Parameter TROLL 9500 is
permanently-installed and factory-calibrated. It may be a turbidity
sensor alone or a pressure/turbidity sensor combination. If your MP
TROLL 9500 was ordered without a turbidity sensor or a pressure
sensor, there will be a permanently installed plug in the pressure/tur-
bidity sensor slot. A turbidity sensor or combination pressure/turbidity
sensor can be added at the factory.
The In-Situ turbidity sensor is comprised of a matched solid-state
detector-emitter pair positioned at right angles. The light source is an
infrared LED, optimized for operation at 870 nanometers (nm). The
optical windows of the detector (photodiode) and emitter (LED) are
SCRATCHRESISTANTSAPPHIRE)3/HASSETADETECTIONANGLEOF½
and the light wavelength at 860 nm. The sensor uses active modula-
tion for ambient light rejection.
The In-Situ sensor is an electronic nephelometer which compares
THEINTENSITYOFLIGHTSCATTEREDBYTHEENVIRONMENTALmUIDWITHINTENSITY
of light scattered by a standard reference suspension. The higher
the intensity of scattered light, as measured in NTU’s, the higher the
turbidity. This measurement generally provides a very good correla-
tion with the concentration of particles in the water that affect clarity.
However, measurements of scattered light cannot be directly related
to a gravimetric equivalent, such as suspended sediment load, unless
a working curve for the specific sample is created.
THE TURBIDITY WIPER
The optional wiper accessory helps to keep the turbidity sensor optics
free of bubbles and fouling.
The wiper installs in port 3 of the MP TROLL 9500 like other remove-
able sensors. A positional brace aligns it with respect to the turbidity
sensor and keeps it stable in moving waters.
The wiper pad is adhesive-free, low-abrasion cotton material. The
pad is easily replaced when it becomes too soiled to clean the sensor
optics effectively.
Use of the wiper will significantly impact battery life. Lithium
batteries are recommended.
SECTION 18: TURBIDITY