Turbidity Sensor (NTU)

The online Turbidity Monitor (nephelometer, turbidimeter) from Chemtrac incorporates a unique Turbidity Probe using LED optical technology to provide an extremely stable, accurate, low maintenance sensor. Combining the sensor with a HydroACT Analyzer/Controller, the system determines true online turbidity and/or suspended solids in water, using a nephelometric measurement of scattered light in accordance with ISO 7027.

This online turbidity meter represents a breakthrough in measurement technologies in that it automatically varies the light output so that the turbidity can be measured independently of background light and electronic drift. Ranging from 0.01 NTU to 1000 NTU with a resolution in the 0 to 10 NTU range of 0.001, the online turbidity monitor provides:

  • Excellent resolution
  • Single point calibration
  • The simplicity of a probe
  • Great value for money
  • Long term reliability
  • Auto-clean for very low maintenance
  • Downloads

  • Description

    Each probe is equipped with a light source, a side detector for the nephelometric measurement of scattered light from the sample and a reference detector for monitoring the light output. The light source is a long-life IR LED emitter. This configuration allows accurate and reliable measurements of online turbidity and suspended solids to be made. Reliable calibration can be carried out using a single calibration with no need for a ‘zero’ adjustment.

    The probes are constructed of stainless steel and sapphire so they can withstand demanding operating environments. An Autoclean system can be included to keep the optical surfaces clean, thereby reducing maintenance to a potential ‘maintenance-free’.

    The online turbidity meter is suitable for dip monitoring and mounting in a de-bubbling flow cell.

    The operating principle of the online turbidity meter is subject to a patent application and is unique in the way it handles the data it receives in order to calculate a zero, to calibrate and to derive the NTU (FNU) value from the readings.

    The Chemtrac online turbidity meters are available with different HydroACT controller options, giving you the same great performance with different communication, display, and control capabilities.

    Standard Features

    • Single point calibration – very easy to use
    • 0.001 resolution
    • Stable and reliable readings – excellent process control

    Optional Features

    • Autoclean solid state optical sensor – no moving parts
    • Dip mount for a channel or tank
    • De-bubbling flow cell


    • Suitable for potable, waste and process waters between 0 NTU and 1000 NTU‘
    • Maintenance-free’ – low cost of ownership
    • No ‘zero’ required – improved accuracy at the low end
    • Up to 1 year between calibration – very little drift
    • Up to 10 bar – for inline operation
    • Automatic de-bubbling and bubble removal solutions – no interference from bubbles
  • Specifications

    Range Selectable within 0.01 – 1000 NTU, 0.01 – 20000 mg/l (application dependent)
    Typical Ranges: 0.01 – 20 NTU, 0.01 – 100 NTU, 0.01 – 1000 NTU
    Linearity: R2 > .99
    Response Times: T90 > 10 sec (adjustable based on averaging)
    < 1% of measured value or 0.01 NTU (whichever is greater)
    Repeatability: < 0.3% of measured value or 0.005 NTU (whichever is greater) (Ref: ISO 15839)
    Resolution: 0.001 NTU (0-2), 0.01 NTU (2-10), 0.1 NTU 910-100), 1 NTU (>100)
    Limit of Detection: 0.001 NTU (0-2), 0.01 NTU (2-10), 0.1 NTU 910-100), 1 NTU (>100)
    Temperature: 0-50o C
    Pressure: 0-10 Bar
    Averaging: 10 sec – 10 min
    Lamp Source: IR LE, 860nm
    Cleaning Cycles: User settable cleaning cycle time and cleaning time
    Cleaning: Auto-clean water jet
    Enclosure Rating: IP65
    Sensor Environmental Protection: IP68
    Display: Value and alarms and graphs at the same time
    Calibration: One point (zero not required)
    Diameter: 38mm (1.5”)
    Length: 278mm (11”)
  • Applications

    Anywhere where the measurement range is 0.01-1000 NTU (approximately 0-2000 mg/l, application dependent) is a suitable application for the online turbidity monitor.

    Traditional online turbidity monitoring applications where the turbidity monitor is particularly suited:

    • Raw water inlet
    • Settled water turbidity
    • Wastewater effluent turbidity
    • Swimming pool clarity monitoring

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