Worldwide Inline Process Control Solutions

Probe Sensors ASD25-N / ASD25-BT-N

optek ASD25-N Single Channel Absorption Probe

Typical Applications:

  • Cell growth in mammalian cell cultures and bacterial fermentation
  • Algae concentration monitoring
  • Biomass concentrations
  • Crystallization process monitoring


The ASD12-N and ASD25-N absorption sensors are designed for use in pilot and production scale fermenters or bioreactors to precisely measure the growth of microbial or cell cultures as a function of NIR absorption.


A precisely defined and constant LED light beam penetrates the process medium. ASD12-N and ASD25-N use light from 840 nm to 910 nm (NIR). The attenuation of the light intensity, caused by absorption by dissolved substances and undissolved material is detected by a hermetically sealed photodiode.

ASD25-N / ASD25-BT-N

Models ASD25-N and ASD25-BT-N are designed for use in pilot or production scale fermenters or bioreactors. These extremely durable probes are designed for sanitary bioprocess environments and can be used in CIP/ SIP processes.

The ASD25-N is conveniently mounted through a standard 25 mm Ingold –type port and the ASD25-BT-N through a standard 25 mm safety port.

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Technical Data

  1. OPL
  2. Sapphire windows
  3. Detector
  4. Daylight filter
  5. LED light source

No window gaskets used

Measurement principle

1- Channel Absorption of light

Measurement wavelength(s)

840 - 910 nm


1 silicon photodiode (hermetically sealed)

Measuring Range

any measuring range between:

  • 0 - 0.05 to 4 CU
Optical path length

1, 5, 10 or 20 mm

Light source

Hybrid LED (hermetically sealed), 5.4 V DC, 100 mA

typical life span: approx 10 years



Process Adaption

wetted parts: stainless steel 1.4435 (SS 316 L) dF < 1 %, BN2

surface: electro-polished Ra < 0,4 μm

Port connection

OSP25-GS60 (similar Ingold-port)

nominal length:60 and 30 mm

diameter:25 mm

thread:G1-1/4 in. ISO 228/1

OSP25-GS52 (similar safety- port)

nominal length:52 and 30 mm

diameter:25 mm

thread:G1-1/4 in. ISO 228/1

Port gasket

O-ring 18.64 x 3.53 mm EPDM (FDA / USP Class VI), others on request

Insertion depth

35 mm + OPL with port length 60 mm

35 mm + OPL with port length 52 mm

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
  • optek T-pieces DIN 11850
  • optek T-pieces OD (BS4821-1)
  • weld-in ports
    Temperature Ratings
    Process temperature

    permanent:5 - 65°C (41 - 149°F)

    peak (60 min./day):5 - 135 °C (41 - 275 °F)

    thermal shutdown at approximately 75 °C (167 °F)

    Ambient temperature

    operation:0 - 40 °C (32 - 104 °F)

    transport:-20 - 70 °C ( -4 - 158 °F)

    Sterilization conditions

    Autoclaving not possible

    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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