MLSS Analyzers SS400G, SS300G

The SS400 MLSS analyzer is a measuring system best suited to continuously and consistently measure the concentration of mixed liquor suspended solids (MLSS) in an activated-sludge treatment process found in sewage or industrial wastewater treatment facilities.

The SS400G MLSS converter has a measuring range as wide as 500-20000 mg/l (ppm). Microprocessor-based, it has a wealth of self-diagnostic functions and alarm contact outputs like other converters in the EXA series, as well as excellent operability.

The SS300G MLSS sensor uses a measuring method that compares transmitted light with scattered light. The sensor is designed with due care to the arrangement of the optical system. These design features enable measurement of even low concentrations, making the sensor less susceptible to disturbing light. The optional jet cleaning unit permits continuous and consistent measurement even in an application where the sensor is exposed to contaminants.

A self-cleaning floating holder is available in addition to free-standing and immersion models, offering a wide range of choices according to the application needs.



  • Wide output ranges, 0-1000 mg/l to 0-20000 mg/l.
  • Output in different two ranges.
  • Abundant contact outputs.
  • Enhanced self-diagnosis functions including failure in light source.


  • Easy-to-maintain, lightweight, compact probe-like sensor.
  • Virtually no need for replacing light source and photodetector unit.
  • Pulse-driven light emission, eliminating effects of disturbing light.
  • Arrangement of optical system highly immune to effects of light reflecting from boundary surface.
  • Choice of jet cleaning unit.
  • Choice of various type of holders according to application needs.


Measuring object Concentration of mixed liquor suspended solids (MLSS) in an aeration tank in a sewage or industrial wastewater treatment plant
Measuring method Transmitted/scattered light comparison method
Measuring range 500 to 20000 mg/l
Output signal Two outputs, 4 to 20 mA DC; maximum load resistance: 600 Ω
Output range Minimum 0 to 1000 mg/l
Maximum 0 to 20000 mg/l
Contact output Four outputs
Contact input Voltage-free contact for remote range selection and start of cleaning
Ambient temperature -10 to 55℃
Relative humidity 10 to 90% RH (non-condensing)
Construction Complies with JIS C0920 watertight, IEC IP65 and NEMA 4X standards
Supply voltage 100 to 240 V AC, 50/60 Hz, 24 V DC
Power consumption 22 VA maximum (AC power)
5 W maximum (DC power)
Weight Approx. 2.5 kg


Shape Probe-like Sensor
Measuring object Concentration of mixed liquid suspended solid (MLSS) in an aeration tank in a sewage or industrial wastewater treatment plant
Measuring principle Scattered/transmitted light comparison method
Measuring range 500 to 20000 mg/l
Temperature of measured object 0 to 50℃
Pressure of measured object 0 to 200 kPa
Flow velocity 1 m/sec maximum
Cable length 3, 5, 10, 15 or 20 m
Material of wetted part or junction Body; Stainless steel (304SS or equivalent)
Window; glass
O-ring; nitrile rubber
Cable; PVC
Weight Approx. 0.5 kg plus N x 0.12 kg, where N is cable length
Cleaning unit (optional) Jet cleaning
Note: No cleaning unit can be used if the sensor is equipped with a floating ball holder.
Material of wiper cleaning unit Nitrile rubber and 304SS (wetted part)
Material of jet cleaning unit Polypropylene, polyethylene and 304SS (wetted part)
Ambient temperature -10 to 50℃
Construction Complies with JIS rainproof standard
Linearity ±4.5 % F.S. (by stable kaolin)
Repeatability 2 % F.S. (by stable kaolin)
Stability Zero: ±2 % F.S./day (by city water)
Span: ±2 % F.S./day (by calibration kit)



In a batch tank, analyzers such as dissolved oxygen (DO) analyzers, oxidation-reduction potential (ORP) meters, and mixed liquor suspended solid (MLSS) analyzers are used. To reduce the maintenance frequency, measures must be taken to prevent dirt accumulation on the sensor. As the liquid level in a tank can vary greatly, great care should be taken when selecting the sensor installation position in a tank.


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