Endress+Hauser COS61 Optical Dissolved Oxygen Sensors

Technical Dossier

Product Details And Specifications

Endress+Hauser COS61 Series: Comprehensive Module Range and Technical Overview

The Endress+Hauser COS61 series represents a mature, field-proven line of optical (luminescence-based) dissolved oxygen sensors deployed across global heavy industry: municipal and industrial wastewater treatment plants, pharmaceutical fermentation processes, aquaculture facilities, food and beverage production, and chemical process monitoring. Unlike polarographic predecessors, the COS61 platform operates on the principle of dynamic luminescence quenching, eliminating the need for electrolyte replacement and reducing maintenance intervals significantly. The series has accumulated substantial installed base in continuous bioprocess monitoring and effluent compliance measurement, where sensor drift and calibration stability are critical operational parameters.

The Evolution of COS61 Architecture

The COS61 series was introduced as part of Endress+Hauser's Memosens digital sensor platform strategy, which standardized inductive, non-contact signal and power transmission between sensor and transmitter. Early COS61 variants used analog 4–20 mA output with direct cable connection. The transition to Memosens protocol (COS61D suffix variants) introduced galvanically isolated digital communication, enabling plug-and-play sensor exchange, pre-calibration in the laboratory, and full traceability of calibration data stored on the sensor chip itself.

Architecturally, the COS61 uses a replaceable optical cap (sensing element) containing the luminophore coating, which is the primary consumable. The sensor body (the COS61 model itself) is the reusable structural component housing the optical transceiver and electronics. This two-component design separates the wear item from the capital asset, a significant lifecycle cost consideration for high-volume installations. Compatibility between sensor bodies and optical caps must be verified by generation: first-generation caps are not interchangeable with Memosens-generation bodies without adapter verification.

The series interfaces with the Endress+Hauser Liquiline transmitter family (CM442, CM444, CM448) and the Liquisys M COM253/COM254 transmitters for legacy installations. Field bus integration is achieved via the transmitter layer, not the sensor itself.

COS61 Full Catalog & Functionalities (SKU List)

The following SKUs represent verified, commonly deployed models within the COS61 series. Classification follows sensor variant and output protocol:

Optical DO Sensor Bodies — Analog Output

• COS61-A1F0: Optical DO sensor, analog output, 120 mm insertion length, standard process connection, no ATEX
• COS61-A2F0: Optical DO sensor, analog output, 220 mm insertion length, standard process connection, no ATEX — extended immersion depth for deeper tanks and open channels
• COS61-A3F0: Optical DO sensor, analog output, 320 mm insertion length, suitable for deep basin installations
• COS61-A1F1: Optical DO sensor, analog output, 120 mm, with integrated temperature measurement (Pt1000)
• COS61-A2F1: Optical DO sensor, analog output, 220 mm, with integrated Pt1000 temperature compensation

Optical DO Sensor Bodies — Memosens Digital Protocol

• COS61D-A1F0: Memosens digital DO sensor, 120 mm, standard process connection, no ATEX — digital inductive signal transmission
• COS61D-A2F0: Memosens digital DO sensor, 220 mm, standard process connection — most widely deployed Memosens variant
• COS61D-A3F0: Memosens digital DO sensor, 320 mm insertion length, deep-tank configuration
• COS61D-A1F1: Memosens digital DO sensor, 120 mm, with Pt1000 temperature sensor integrated
• COS61D-A2F1: Memosens digital DO sensor, 220 mm, with Pt1000 temperature sensor integrated
• COS61D-A1F2: Memosens digital DO sensor, 120 mm, ATEX Zone 1/21 certified, for use in explosive atmospheres
• COS61D-A2F2: Memosens digital DO sensor, 220 mm, ATEX Zone 1/21 certified

Optical Caps (Sensing Elements / Consumables)

• COS61-Z1: Standard optical cap for COS61 analog series — luminophore sensing element, replacement consumable
• COS61D-Z1: Standard optical cap for COS61D Memosens series — compatible with all COS61D body variants
• COS61D-Z2: Extended-life optical cap, enhanced luminophore formulation for high-fouling environments (activated sludge, industrial effluent)

Accessories & Mounting Hardware

• COS61-Z3: Immersion assembly / retractable fitting adapter for COS61 series, DN25 process connection
• CYK10: Memosens connecting cable, sensor-to-transmitter, standard length variants — required for COS61D field wiring

Sourcing Hard-to-Find & Obsolete COS61 Parts

The COS61 analog output variants (non-Memosens) have entered end-of-life status in Endress+Hauser's standard product portfolio. OEM lead times for these models are extended or unavailable through standard distribution channels. DriveKNMS maintains a dedicated inventory of COS61 analog sensor bodies and optical caps sourced through authorized secondary market channels, enabling lifecycle extension for installations not yet migrated to Memosens architecture.

For plants operating legacy Liquisys M COM253/COM254 transmitters that are not compatible with Memosens sensors without hardware upgrade, DriveKNMS provides matched analog COS61 units tested against original E+H factory specifications. This service is specifically relevant to wastewater treatment facilities operating under long capital replacement cycles (10–20 year asset life) where transmitter replacement is not budgeted.

All sourced units are accompanied by full traceability documentation. Batch records, calibration certificates, and condition reports are provided upon request for regulated industries (pharmaceutical, food and beverage) requiring supplier qualification documentation.

Quality Control for the COS61 Range

COS61 sensors undergo a structured incoming inspection and functional verification protocol at DriveKNMS before dispatch:

• Optical cap integrity check: Visual and spectroscopic verification of luminophore coating condition. Degraded or contaminated caps are rejected and replaced.
• Sensor body electronics test: Signal output verification across the full measurement range (0–20 mg/L O₂) using calibrated reference gas mixtures (nitrogen for zero-point, ambient air for span).
• Temperature sensor verification: Pt1000 resistance measurement at reference temperature for models with integrated temperature compensation.
• Memosens communication test (COS61D variants): Inductive coupling integrity and data transmission verification using Endress+Hauser Field Xpert or equivalent Memosens diagnostic tool. Sensor memory (calibration history, serial data) is read and documented.
• Mechanical inspection: Process connection thread condition, O-ring seating surfaces, and cable entry integrity assessed for all units.

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