YSI EXO Optical Dissolved Oxygen Sensor

The EXO optical dissolved oxygen sensor is a digital smart sensor featuring welded titanium construction and wet-mateable connectors.


  • 0 to 50 mg/L measurement range
  • T63<5 sec response time
  • ±0.1 mg/L or 1% of reading accuracy from 0 to 20 mg/L
Your Price $2,200.00

The EXO optical dissolved oxygen sensor is a digital smart sensor featuring welded titanium construction and wet-mateable connectors. For long-term, in situ continuous monitoring of dissolved oxygen, the EXO2 and EXO3 sondes have a wiper to clean the dissolved oxygen sensor to avoid sensor fouling and maintain accuracy.

The principle of operation of the EXO optical dissolved oxygen sensor is based on the well-documented concept that dissolved oxygen quenches both the intensity and the lifetime of the luminescence associated with a carefully chosen chemical dye. The EXO DO sensor operates by shining a blue light of the proper wavelength on this luminescent dye which is immobilized in a matrix and formed into a disk. The blue light causes the immobilized dye to luminesce and the lifetime of this dye luminescence is measured via a photodiode in the probe. To increase the accuracy and stability of the technique, the dye is also irradiated with red light during part of the measurement cycle to act as a reference in the determination of the luminescence lifetime.

When there is no oxygen present, the lifetime of the signal is maximal; as oxygen is introduced to the membrane surface of the sensor, the lifetime becomes shorter. Thus, the lifetime of the luminescence is inversely proportional to the amount of oxygen present and the relationship between the oxygen pressure outside the sensor and the lifetime can be quantified by the Stern-Volmer equation: ((Tzero/T) – 1) versus O2 pressure. For most lifetime-based optical DO sensors, this Stern-Volmer relationship is not strictly linear (particularly at higher oxygen pressures) and the data must be processed using analysis by polynomial non-linear regression. Fortunately, the non-linearity does not change significantly with time so that, as long as each sensor is characterized with regard to its response to changing oxygen pressure, the curvature in the relationship does not affect the ability of the sensor to accurately measure oxygen for an extended period of time.

Questions & Answers
How long until the sensor cap needs replaced?
A typical usable life is 12-18 months depending on usage. Sensors deployed continuously should generally be replaced annually.
Can I use this sensor with other sondes or meters?
No, this sensor is only compatible with the EXO sonde platform.
Are anti-fouling measures needed for this sensor?
You can use the following products to help mitigate biological fouling in the field: YSI EXO Central Wiper, YSI EXO Anti-Fouling Copper-Alloy Sonde Guard, YSI Anti-Fouling Copper Tape.
My replacement membrane did not come with any tools. What do I need to replace the membrane?
The EXO membrane does not require any tools for replacement. It can simply be threaded on and off, making replacement easier and more convenient.
Can I change sondes without needing to re-calibrate my sensor?
Yes, all EXO sensors have their own internal memory that allows them to hold calibration.
How much pressure can the YSI EXO Optical Dissolved Oxygen Sensor withstand?
The EXO dissolved oxygen sensor integrates with the EXO sondes, which have a depth range of 0-250m.
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