Worldwide Inline Process Control Solutions

Probe Sensors ASD12-N / ASD19-N

optek ASD12-N Single Channel Absorption Probes

Typical Applications:

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


The ASD12-N, ASD19-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, ASD19-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.


The ASD12-N probe is specifically engineered for use in laboratory fermenters. The seal-less sapphire window design eliminates crevices and gaps to assure the highest level of sterility. All wetted parts are electro-polished steel. The ASD12-N is autoclavable and mounts conveniently through any headplate with a PG13.5 threaded port. The ASD12-N is available in three different insertion depths with either 5 or 10 mm OPLs (optical path length = distance between the windows). Shorter optical path lengths are typically used for dense cell cultures such as bacterial and yeast cultures. Longer OPLs are used for less dense cell cultures e.g., mammalian cells and dissolution / precipitation / crystallization reactions.


The ASD19-N, based on the same design as the ASD12-N with seal-less window construction, is typically used in larger fermenters or bioreactors. Connection is through a standard 19 mm port (M26 x 1) in the fermenter or bioreactor headplate. The ASD19-N is available in three different insertion depths and with OPLs of 1 mm, 5 mm, 10 mm or 20 mm.

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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

5 or 10 mm others on request

1, 5, 10 or 20 mm


CU (concentration units) application specific calibration

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

housing: stainless steel 1.4571 (SS 316 Ti)

Port connection

Fermenter head plates

diameter:12 mm

thread:PG 13.5

Fermenter head plates

diameter:19 mm

thread:M26 x 1

Port gasket

O-ring 11.00 x 3.00 mm


O-ring 15.60 x 1.78 mm


Insertion depth

110 mm + OPL

215 mm + OPL

315 mm + OPL

others on request

140 mm + OPL

210 mm + OPL

310 mm + OPL

others on request

Process pressure


(+/- 0.5 bar) (+/- 7.25 psi)

10 mbar to 10 bar

(0.15 psi to 145 psi)


Sapphire (seal-less)

Installation accessories

Adapter PG 13.5 Variable depth

Adapter M 26 x 1 - PG 13.5

special adapters on request

Temperature Ratings
Process temperature

permanent:5 - 50°C (41 - 122°F)

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

Sterilization must be performed outside the process and the ASD must be disconnected from the power source

(autoclaving possible without cable)

max. pressure: 4 bar (58 psi)

max. temperature: 135 °C (275 °F) (max. 60 min./day)

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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