Version 2.1
Update: April 2016
PONSEL Mesure – Aqualabo Contrôle
35 Rue Michel Marion – 56850 CAUDAN, FRANCE
Tel.: +33(0)2 97 89 25 30 – Fax: +33(0)2 97 76 55 72
7.2.2 NTU sensor: Turbidity.
Turbidity: nephelometric measurement by IR diffusion (wavelength: 880 nm)
at 90°.
Temperature: NTC thermistor.
PVC, PMMA, Polyamide, POM-C, polyurethane sleeve on cable
The optical windows are sensitive to:
- chemicals (organic solvents, strong acids and bases, hydrogen
peroxide, hydrocarbons),
- mechanical stresses (impacts, abrasion).
When in use, the sensor must not come into contact with the sides or bottom
of a container. Maintain a minimum distance of 2 or 3 cm between the sides
and the sensor (depending on the concentration of the medium).
Bubbles on the optical components can interfere with the measurements.
When immersing the sensor in the medium to be measured, wait until the
sensor's temperature has stabilized before taking the reading.
If measurements are being made in a range between 0 and 20 NTU, or if the
sensor saturates (a value of 9999), it is advisable to use the protective sieve
to avoid interference from edge effects, sunlight, etc.
After each use, rinse the sensor carefully in clean water.
If deposits such as biofilm or sludge persist, clean the sensor carefully with
soapy water and wipe the head with a soft cloth or absorbent paper.
Place the protective bag over the head of the sensor to prevent the optical
part from being scratched.
Turbidity calibration (in
NTU)
The NTU sensor is an optical sensor which requires very little calibration.
Using a clean sensor, occasionally check the 0 NTU value by immersing the
sensor in clean, bubble-free water. If there is a zero error, perform a complete
calibration of the sensor (over 1 or 4 measurement ranges).
This procedure requires a formazine solution whose concentration lies
at the mid-point of the measurement range being calibrated. This
solution is prepared from a 4,000-NTU stock solution.
Use a 200 ml volumetric flask when preparing the solutions. Add the required
volume of formazine (refer to the table below) and make up to 200 ml with
distilled water.
Formazine solutions with concentrations of less than 1,000 NTU degrade
fairly quickly; do not keep the solution for more than a few days.
The 2,000 NTU solution can be kept for 2 to 3 weeks in a fridge in an opaque
bottle.
Concentration of
formazine standard
solution
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