Xylem WQ770-B TURBIDITY METER - Manual (Page 8)

Global Water
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VIII. Appendix A: Turbidity Meter Calibration
Note: The following steps show how to calibrate the WQ770 Turbidity
Sensor using suspended polymer turbidity standards only.
General
a. The Turbidity Sensor is measuring turbidity in liquids by using a 90
degrees scatter nephelometer where a focused beam is directed into
the monitored water. The principle is based on recommendations of
the international guideline ISO 7027
.
Two detectors receive light from
a source emitting 880 nm infrared light in a pulsed mode. One
detector is placed opposite the source, receiving the transmitted light,
and the other detector is placed at an angle of 90 degrees to the
incident light beam measuring side-scattered light. The detected light
intensity is directly proportional to the turbidity of the water.
b. The following supplies are required:
Stand with rod and clamp
Beakers, 500 or 1000 ml
1000 NTU Turbidity Standard
50 NTU Turbidity Standard
0.0 NTU Turbidity Standard
Distilled Water
The preferred and recommended turbidity standards are suspended
polymer solutions. These are EPA approved, non-toxic, and require
no mixing or stirring. Other types of standards such as Formazin can
also be used, but these require thorough mixing and must be used
with low speed stirring plates during the calibration process.
All the necessary turbidity standard solutions are available from Global
Water, contact the sales department for more information. See
Appendix B.