Worldwide Inline Process Control Solutions

Turbidity Sensor TF56-N

optek TF56-N Scattered Light Dual Channel Turbidity Sensor

optek TF56-N Scattered Light Dual Channel Turbidity Sensor

Typical Applications:

  • Filter control
  • Heat exchanger leak detection
  • Lauter tun in brewery
  • Liquid sugar clarity


Model TF56-N is a precision turbidity sensor for use in various industries. The sensor is designed for inline operation and provides accurate concentration measurements with remarkable repeatability, linearity and resolution.

Modular construction of the sensor offers maximum flexibility in adapting to various process needs. Options include electro-polished sensor bodies, chemical resistant materials, (sapphire windows, titanium, Hastelloy, etc.) and high temperature or high pressure versions.

TF56-N (Scattered Light / Turbidity)

Light scattered from particles (trace suspended solids, undissolved liquids or gas bubbles) in the medium is detected by four hermetically sealed silicon photodiodes at an angle of 11°. At the same time, the unscattered light is detected by a reference photodiode.

This unique dual channel design compensates for disturbances of the carrier medium. The sensor can be calibrated in ppm (DE), EBC or FTU and measures extremely low particle sizes and concentrations.

Special optical windows are made from a single crystal sapphire, providing superior resistance to all abrasive and corrosive media. With the appropriate choice of sensor bodies and a broad variety of line sizes available, the TF56 can be easily adapted to the process.

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Technical Data

  1. Sensor Body
  2. Windows
  3. Focusing optics
  4. Detector 0° (Abs.)
  5. Four 11° detectors
  6. Optics Module
  7. Lamp module
Measurement principle

2- Channel Scattering of light (11°)

Measurement wavelength(s)

730 nm - 970 nm


1 silicon photodiode (hermetically sealed)(Abs.)

4 silicon photodiodes (hermetically sealed) (11°)

Measuring Range

any measuring range between

0 - 25 to 500 ppm (DE)

0 - 10 to 200 FTU

0 - 2.5 to 50 EBC

Optical path length

40 mm standard

(50 - 60 mm with reduced accuracy)


basic calibration 11°: in ppm (DE) / FTU / EBC

Light source

special incandescent tungsten lamp 5.0 V DC, 970 mA

typical life span: 3 to 5 years (25,000 to 40,000 hours)


< ± 0.5 % of respective measuring range


< ± 1.0 % of respective measuring range


< ± 2 % of respective measuring range (specific to application)


all optical parts have an IP rating of IP65 or higher

Sensor Body

Stainless steel 1.4435 (SS 316L), 1.4539, 1.4571 (SS 316Ti), 1.4462, Titanium 3.7035 (Grade 2), Hastelloy 2.4602 (C22), Plastic TFM4215, PVC, ... others on request

Line size

1/4 in. to 6 in. (DN 6 to DN 150), ... others on request

Process connection

Flanges (ASME, DIN, JIS), Clamps (TC, ISO, DIN), Female Threads (NPT, DIN), Sanitary Threads (DIN 11851), Tube Ends (DIN, ISO, OD), Varivent, ... others on request

Process pressure

10 mbar to 100 bar (0.15 psi to 1450 psi) - higher on request depending on process connection, materials and design


1-Pyrex®, 2-Sapphire, 3-Sapphire Biotech

Window gaskets

Silicone (FDA), Viton® (FDA), EPDM (FDA / USP Class VI), Kalrez® 4079, ... others on request

Temperature Ratings
Process temperature

permanent:0 – 100 °C (32 – 212 °F)

peak (15 min/day):0 – 120 °C (32 – 248 °F)

Process temperature

permanent:-20 °C - 190 °C (-4 °F - 374 °F)

peak (15 min/day):-20 °C - 210 °C (-4 °F - 410 °F)

Ambient temperature

operation:0 - 40 °C (32 - 104 °F)

operation:-20 - 40 °C (-4 - 104 °F) with option HT

transport:-20 - 70 °C ( -4 - 158 °F)

Pressure and temperature ratings specified herein may be subject to limitations - see instruction manual. The appropriate choice of material for all wetted parts is the sole responsibility of the user. Data given are subject to changes without prior notice.

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