Worldwide Inline Process Control Solutions

VIS/NIR Probe Sensor AS56

optek AS56-N Single Channel Absorption Probe

Typical Applications:

  • Milk/water phase separation (AS56-N)
  • Beer/yeast phase separation (AS56-N)
  • Beer/water phase separation (AS56-F)
  • Inlet separator control (AS56-N)


Models AS56 are high precision sensors measuring turbidity (AS56-N) or color (AS56-F) for use in various industries. The sensors are designed for inline operation and provide accurate concentration measurements with remarkable repeatability, linearity and resolution.


The AS56, based on the same design as the AS16 has wetted parts made from electro-polished stainless steel and a seal-less window construction. It is typically used in food and beverage applications to allow cost-effective measurements (e.g., phase separation).

NIR-Absorption (Turbidity) VIS-Absorption (Color)

A special tungsten lamp produces a constant light beam that passes through the process medium. The attenuation of the light intensity, caused by absorption and/or scattering by dissolved and undissolved substances, is detected by a sealed silicon photodiode. AS56-N uses light from 730 - 970 nm to measure solids concentration independent from color or color changes (e.g., yeast concentration in beer during tank draining).

AS56-F uses a specific wavelength of 430 nm in the visible spectrum to measure color in liquids with little or no turbidity (e.g., beer in water during phase change).


optek AS56-N Single Channel Absorption Probe

Special optical windows are made from a single crystal sapphire, providing superior resistance to all abrasive and corrosive media. optek superior manufacturing techniques allow mounting the windows without gaskets or glue for a lifetime without maintenance. The appropriate choice of the optimum OPL (optical path length = distance between the windows) supports all measurement requirements, i.e., low/high measuring ranges at highest resolution.

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Technical Data

  1. OPL
  2. Windows
  3. Lamp module
  4. Optics modules (incl. filter)
  5. Detector module

No window gaskets used

Measurement principle

1- Channel Absorption of light

Measurement wavelength(s)

AS56-N:730 - 970 nm

AS56-F:430 nm


1 silicon photodiode (hermetically sealed)

Measuring Range


any measuring range between

0 - 0.05 to 4 CU


any measuring range between

0 - 0.05 to 1.5 CU

Optical path length

5 or 10 mm


CU (concentration units) application specific calibration

Light source

special incandescent tungsten lamp 5.0 V DC, 450 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

Process Adaption

wetted parts: stainless steel 1.4435 (SS 316 L)

surface: electro-polished Ra < 0,8 μm

housing: stainless steel 1.4571 (SS 316 Ti)

Port connection

thread G1-1/4 in., ISO 228/1 for port AS25 (similar Ingold-port)

diameter: 25 mm ( D= 25 H7)

O-ring groove for 30 mm and for 60 mm port length

Port gasket

O-ring 18.64 x 3.53 mm EPDM (FDA / USP Class VI)

Insertion depth

35 mm (1.38 in.) + OPL at a port length of 60 mm (2.36 in.)

Process pressure

10 mbar to 10 bar (0.15 psi to 145 psi)


Sapphire (seal-less)

Installation accessories
  • weld-in ports
  • Varivent adapter (50.00)
  • clamp adapter (1.5 and 2.0 in.)
  • optek T-pieces DIN 11850 (DN50 - DN100)
  • optek T-pieces OD (BS4821-1) (2.0 - 4.0 in.)
Temperature Ratings
Process temperature

permanent:0 - 90 °C (32 - 194 °F)

peak 60 min/day:0 - 100 °C (32 - 212 °F)

Ambient temperature

operation:0 - 40 °C (32 - 104 °F)

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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