Dissolved Oxygen Analyzers

Yokogawa offers dissolved oxygen (DO) analyzers that work with the three common technologies for dissolved oxygen measurements: polarographic, galvanic and optical. Our dissolved oxygen analyzers provide high precision measurement and are built to withstand the harshest applications, requiring minimum maintenance and helping you achieve increased efficiency and reduced operating costs. The standard units of measure are milligrams per liter (mg/l), parts per million (ppm), parts per billion (ppb), or % saturation.



  FLXA202 FLXA402

Area Classification General Purpose, Class I Div II, Class I Div I General Purpose, FM Class I Div II pending
Power Supply 2-Wire Loop Powered 24VDC 4-Wire 100-240 VAC; 4-Wire 12-24 VDC
Communication 4-20mA, HART 4-20mA, HART, Ethernet (Modbus TCP), RS-485 (Modbus RTU)
Contacts and Relays N/A 4 SPDT relay contacts with display indicators



What Is a Dissolved Oxygen Analyzer?

Dissolved Oxygen meters, analyzers, and transmitters are used for continuous process measurement and monitoring of milligrams per liter (mg/l), parts per million (ppm), parts per billion (ppb), or % saturation.

Dissolved Oxygen Analyzer Working Principle:

When oxygen dissolves in water, it acts as a chemical oxidizer. Water temperature, barometric pressure, salinity, etc. all affect oxygen's water solubility, which decreases with increases in water temperature.

Oxygen meter sensor measurement methods include the membrane electrode method (galvanic cell and polarographic). 

Dissolved Oxygen Controller Industrial Applications Include:

  • Primary and secondary water treatment
  • Water Purification

Benefits of a Dissolved Oxygen Analyzer:

Dissolved oxygen analyzers are one of Yokogawa's sustainable solutions for the environment, for society, and for our customers. This innovative wastewater industry solution utilizes energy-efficient technology that improves automation processes and provides real-time data visibility to enable agile responses to business and market dynamics. For example, our modular design series of online dissolved oxygen analyzers and portable dissolved oxygen analyzers offer single- or multi-sensor measurement.

Four-Wire vs. Two-Wire Analyzers

What is a 4-wire analyzer?

This terminology only refers to the power supply of the analyzer. It does not have any reference to the number of wires. The 4-wire analyzers separate the power supply from the measurement output. As a minimum, we need two wires for the power supply and two wires for the current output of the analyzer. The FLXA402 has two analog outputs. four digital outputs. One digital input and of course the sensor input wiring. That is why FLXA402 has 6 cable glands. The advantage is that any functions are combined in one enclosure. Local control and alarm functions are possible. In small control installations, this is a cost-saving feature.

What is a 2-wire analyzer?

The 2-wire analyzers commonly referred to as Analyzers combine the wires for current output, for power supply and digital communication. The FLXA202 combines the power supply with mA output and HART® communication: all with only two wires plus shield. The advantage is safety (only 24VDC) and simple installation. Just two wires between the control room and analyzer. This is an advantage in large scale operations where process control is centralized in the DCS system. 


The input module you need depends on the Model Number of your FLXA Analyzer.

The input module you need depends on the Model Number of your FLXA Analyzer.

Click the link at the top of the page to download the DO400 Manual.

Get the most from what exists currently and take advantage of new methods. Appeared in the March 2021 issue of an ISA.org publication.




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