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Digital oxygen sensor
Oxymax COS51D

Digital oxygen sensor
Oxymax COS51D ©Endress+Hauser

The concentration of oxygen dissolved in a liquid can be measured using the amperometric or optical measuring principles. This video shows what it is about and how these measuring principles work.

Memosens converts the measured value to a digital signal and transfers it to the transmitter without a contacting connection. This video shows how Memosens optimizes process control and maintenance.

Memosens amperometric oxygen sensor for water, wastewater and utilities

Oxymax COS51D is a reliable and highly accurate oxygen sensor for all kinds of water & wastewater applications (including hazardous areas). Designed to be low-maintenance with a long operating life, the sensor offers outstanding value for money. Thanks to Memosens digital technology, the Oxymax COS51D combines maximum process and data integrity with simple operation. It resists corrosion and moisture, enables lab calibration and facilitates predictive maintenance.

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  • Benefits

    • Maximum measurement accuracy

    • Logging of sensor load data for easy traceability

    • Intelligent, self-monitoring sensor

    • Minimum calibration effort thanks to simple air calibration

    • Long maintenance intervals

    • Approved for hazardous area use

  • Field of application

    Oxymax COS51D measures the dissolved oxygen concentration in:

    • Wastewater treatment plants:
      - O2 control in the aeration basin
      - Process water treatment and monitoring

    • Water works:
      - Status monitoring of drinking water (oxygen enrichment, corrosion...

Features and specifications



  • Measuring principle

    Sensor Oxygen

  • Application

    Aeration tank, river monitoring, water treatment, fish farming, sewage treatment plants

  • Characteristic

    Amperometric 3-electrode longterm-stable sensor to measure dissolved oxygen

  • Measurement range

    0.01 to 100 mg/l
    0.00 to 1000 %SAT
    0 to 2000 hPa

  • Measuring principle

    Closed membrane covered amperometric 3-electrode system

  • Design

    Digital signal transmission
    Calibration datas stored in the sensor

  • Material

    Sensor body: POM
    Membrane cap: POM

  • Dimension

    Diameter: 40mm (1.57 inch)
    Shaft length: 144 mm (5.67 inch)

  • Process temperature

    -5 to 50 °C
    (20 to 120 °F)

  • Process pressure

    max. 10 bar
    (max. 145 psi)

  • Connection

    Memosens connector
    Process: G1, NPT 3/4"

Documents / Manuals / Software

Accessories / Spare parts

Order code
  • 2
    • Nr 2 Order code 51506976

      Set of 2x membrane cap COY31-WP

      2 pcs. ready made for sensors COS31, COS41 and COS51D standard

    • Nr 2 Order code 51506977

      Set of 2x membrane cap COY31S-WP

      2 pcs. ready made for sensors COS31, COS71 and COS51D (fast)

    • Order code 50053349

      Elektrolyte COY3-F

      10 pcs. plastic ampoules, for sensors COS3/3S/COS4 and COS31/41/51D/71.

  • 1
    • Nr 1 Order code 51506985

      Sealing set COY31-OR

      3 pieces O-rings for sensors COS31, COS41, COS51D and COS71.

    • Order code 51506973

      Polishing foil COY31-PF

      10 pcs. for cleaning of the gold cathode for sensors COS31, COS41, COS51D and COS71.

    • Order code 51506784

      Accessory kit COY31-Z

      Content: COY3-F, COY31-WP, COY31-OR and COY31-PF for sensors COS31, COS41 and COS51D standard

    • Order code 51506785

      Accessory kit COY31-S-Z

      Content: COY3-F, COY31S-WP, COY31-OR and COY31PF for sensors COS31, COS71 and COS51D (fast)

  • 3
    • Order code 51500832

      Junction box RM

      to lengthen the cable for Memosens/CUS31/41. Protection class IP 65, with 2x PG 13.5

    • Order code 50081787

      COY 3-SK membrane protective basket

      for immersion of diss. oxygen sensors COS31/41/51D/61/61D in fish ponds.

    • Order code CYK10-

      Meas. cable CYK10 Memosens

      Application: digital sensors with inductive Memosens plug-in head Working limit: max. -20...135oC

    • Order code CYK11-

      Measuring cable CYK11 Memosens

      Extension cable, Application: digital fixed cable sensors respectively CYK10. Operating temperature range: -30...90oC

    • Order code COY8-

      Zero-point gel COY8

      Zero point: Verification, calibration, adjustment at zero point of oxygen and disinfection sensors ::Amperometric and optical sensors ::12, 25 and 40mm diameter ::Application in the lab, in the field