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P/N: 95343
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Turbidity
Turbidity is measured as the fraction of an infrared light beam that is
scattered at 90° to that beam. More particles in the water mean more of
that light is scattered, so the turbidity reading is higher. Any material
that accumulates on the optical surfaces of the turbidity sensor such as
solids and gas bubbles is indistinguishable from particles suspended in
the water, so most turbidity sensors have wipers to clean the optical
window (the small glass port on the end of the sensor).
Turbidity sensors require no regular maintenance, but you should check
occasionally to make sure the optical window has not been scratched or
damaged by cleaning or accidental contact.
Turbidity uses a two-point calibration; one point is zero turbidity and the other point should be a standard
approximating the turbidity of the water you intend to monitor. Zero calibration can be performed using a
commercial turbidity standard of 0 NTU or with distilled or deionized water. Note that distilled or DI water can
vary in clarity up to about 0.5 – 1.0 NTU, so using it as a 0 NTU standard could affect accuracy of very low
turbidity readings.
Make sure you use enough calibration standard solution to cover the sensor’s “optical volume” – generally,
filling to near the top of the calibration cup when installed on the inverted sonde is sufficient. For the zero
calibration:
1.
Make sure the turbidity sensor is fully immersed (i.e. at least 1 ½ inches of solution over the sensor) in
zero-turbidity standard and has an unobstructed optical path.
2.
Follow the MP252 Control Software’s calibration instructions.
For the second calibration point:
3.
Rinse your sensors several times with the standard you’ll use for calibration.
4.
Make sure the turbidity sensor is fully immersed (i.e. at least 1 ½ inches of solution over the sensor) in
the standard and has an unobstructed optical path.
5.
Follow the MP25 software’s calibration instructions.
A clean, smooth wiper means better measurements. If the wiper pad shows signs of deterioration, it can be
replaced. To change the wiper pad:
1.
Using the 1.5mm hex key that comes with the new wiper pad, loosen the
small set screw on the wiper arm and gently remove the arm. Be careful
not to rotate the wiper arm as this can damage the internal gears.
2.
Remove the wiper pad from the wiper arm and replace the pad.
3.
Place the wiper arm on the motor shaft so that the set screw faces the
flat spot on the motor shaft.
