Optical Dissolved Oxygen Sensors DO71/DO72

See the light by using precise low maintenance SMART optical dissolved oxygen technology

The Yokogawa SMART optical dissolved oxygen sensors DO71 and DO72 have a high degree of durability and stability and require limited maintenance.
Key features of the smart optical DO sensors are fast response time, no warm-up time, and exceptional long-term stability. Qualities that support a high degree of process and cost optimization.

Because of their flat sensor surface and stainless-steel body, the DO71 and DO72 SMART sensors are robust and easy to clean. They are suitable for measurements ranging from low ppb levels to saturated oxygen levels in the water. Ideal for W&WW applications or industrial oxygen monitoring when the sensor needs to be able to withstand challenging measurement environments.

The DO71 and DO72 are digital dissolved oxygen SMART sensors with RS-485-based communication. This feature enables easy calibration in the field, workshop, or laboratory when using the FREE commissioning software "SENCOM ct”.

The sensors' smart functionality enables communication with any other Modbus HOST, such as a PLC, data acquisition system, or other intelligent device, in addition to the Yokogawa FLXA402 analyzer series.

About OpreX

OpreX is the comprehensive brand for Yokogawa’s industrial automation (IA) and control business and stands for excellence in the related technology and solutions. It consists of categories and families under each category. This product belongs to the OpreX Analyzers family that is aligned under the OpreX Measurement category.


Easy to clean and long-time stability for a long time

The DO71/DO72 use a fluorescence phase-shift method, which is less susceptible to contamination than the fluorescence intensity method and allows more accurate measurement.

Excellent maintainability

Maintenance is done only by replacing the sensor cap at the tip, and it can be easily replaced without using any tools.
Because of no electrolyte, it can be used continuously for a long time without maintenance.


Supports a wide range of measurement environments

DO71 and DO72-W for 0 to 22.5 mg/L can be used for wide range applications such as waste water treatment and process control, and DO72-T for 0 to 2 mg/L can be used for low concentration applications such as SWAS. In addition, a variety of cleaning options are available and it is suitable for difficult applications and for strict water quality control.

Simple measurement system and easy installation

The 4-wire liquid analyzer FLXA402 can connect a pH sensor, conductivity sensor, galvanic or polarographic method dissolved oxygen sensor to the second module of FLXA. You can easily customize analyzer according to your process requirements.

Control delicate process measurement processes

With a 90% response time of less than 90 seconds, it can quickly follow the oxygen concentration change of the process.


Principle of Measurement

Optical (fluorescence) measurement method


Combination Product

Multi Channel 4-Wire Analyzer FLXA402

FLXA402 supports various communication functions, and can download/upload DATA with SD card, making installation and DATA management easy.

>> For details, refer to FLXA402, 4-wire liquid analyzer for dissolved oxygen measurement


Paperless Recorder  SMARTDAC+ GX/GP

SMARTDAC+ GX/GP is a modular, versatile paperless recorder with an intuitive touch screen. Equipped with AI as standard.
You can download the configuration file for DO71/DO72 from Customer Portal.
*C3/MT/MC option is required for DO71/DO72 combination.

For details, refer to
>> Paperless Recorder(Panel mount type) GX10/GX20
>> Paperless Recorder(Panel mount type) GP10/GP20

Paperless Recorder  SMARTDAC+ GX/GP

Digital Indicator with Alarms UM33A/S006

UM33A/S006 is an alarm digital indicator with RS485 communication function (Modbus master/monitor) that can display the data of Modbus slave sensors or devices and monitor communication data between Modbus master and slave devices.
*UM33A-S is not available for DO71/DO72.

>> For details, refer to Digital Indicator with Alarms UM33A

Digital Indicator with Alarms UM33A/S006



Water treatment plants such as sewage treatment plants and wastewater sludge treatment plants under severe measurement conditions.
Wastewater treatment plants, environmental applications, and aquaculture measurements
Steam and Water Analysis System (SWAS) etc.

Wastewater Treatment Overview Flow (Compatible models: DO71, DO72 -W)
Wastewater Treatment Overview Flow


SWAS (compatible model: DO72-T)
Example of sewage treatment for a thermal power generation boiler (compatible model: DO72 T)




(with cable)
-W (Wide range) -T (Trace range)
Measurement Range 0 to 22.5 mg/L 0 to 22.5 mg/L 0 to 2 mg/L
Cable Integrated type Separate type Separate type
Operating temperature 0 to 50℃ 0 to 50℃ 0 to 50℃
Pressure 0 to 300 kPa 0 to 1200 kPa 0 to 1200 kPa
Flow rate 2 m/sec or less
Response time ≤ 90 sec. (90% response)