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12
MLSS in DO/MLSS equipment - INTRODUCTION
12.1
Scope
The combination DO-MLSS products are based on the AZTEC Series 5000
Dissolved Oxygen System platform. The range shares common components,
software and procedures and the MLSS sensor is incorporated into the
DO/temperature sensor assembly in the wet end. This section of the handbook
details any additional MLSS-specific features of this product range. It should be
read in conjunction with the main AZTEC DO System section of the manual,
chapters 1 to 11, which contains the main operational information.
All safety, installation and technical references in the
AZTEC DO manual section apply.
12.2
Product Range
The combination DO-MLSS product range currently comprises:
1. Single DO + MLSS.
2. Single DO + MLSS with Local Control Box (LCB)
12.3
Intended Audience
This manual is for reference by all specific, operational or engineering staff using
the equipment.
12.4
Measurement Principles
The measurement of MLSS is made using an optical sensor. The wavelength of light
used for the measurement is 870 nanometres (Infra Red). The light emitted by the
sensor is invisible to the human eye. The light output is pulsed to prevent any
possible interference from ambient sources such as variable sunlight. The Principle of
operation of the AZTEC MLSS Sensor is based upon a technique called
Nephelometry. A Nephelometer measures light reflected by solid particles in
suspension in a liquid. The light is emitted by an infra red LED light source, and the
light intensity is carefully controlled. The higher the concentration of solids in
suspension, the greater the amount of reflected light. In this way, the intensity of
reflected light is used to indicate the amount of solids surrounding the sensor.
The unit of measurement for nephelometric measurements is the Formazin Turbidity
Unit or FTU. Formazin is available as a “Standard” solution that has a reproducible
particle size and “brightness” or reflectivity. This standard is used to initially calibrate
the sensor and amplifying electronics in the factory. The instrument is shipped
accurately calibrated in FTU.
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AZTEC SERIES 5000 DISSOLVED OXYGEN SYSTEM