YSI EXO Optical Dissolved Oxygen Sensor
- 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
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.
In The News
Many algae sensors can detect Chlorophyll a or levels of blue-green algae. YSI’s new Total Algae Sensor can measure both at the same time.
“If you’re only looking at Chlorophyll a, you can miss a very big portion of total algae biomass,” said Tim Finegan, product manager.
The new sensor is an optional attachment to the company’s line of EXO sondes, which debuted earlier this year. It’s an optical probe and maintenance is limited to keeping the sapphire windows on the unit clean.
The Total Algae Sensor can be calibrated in two different ways, one for spot sampling and one for continuous sampling, which allows users to make sure readings are accurate for their specific monitoring applications.Read More
The new YSI EXO Sonde expands monitoring capabilities for users compared to YSI’s the previous generation of sondes. One new feature for the EXO is a fluorescent dissolved organic matter probe that measures light-absorbing particles in water.
The sensor is another attempt by YSI to provide instrumentation options to those in the waste water industry, or anyone interested in measuring dissolved organic matter alongside other parameters.
YSI’s fDOM sensor detects only on a narrow wavelength range. “The wavelength at which (particles) absorb light optimally and then the wavelength that they emit, or fluoresce light optimally, is unique to that molecule,” said Rob Ellison, YSI EXO director of research and development, during a webinar on the fDOM sensor.Read More
A new line of multiparameter sondes is making a splash in the water monitoring market. The recently introduced YSI EXO line offers simpler calibration, more rugged materials and a future-proof design.
The new water quality sondes can measure temperature, conductivity, depth, dissolved oxygen, pH, ORP, total algae (chlorophyll and blue-green algae), turbidity and fluorescent dissolved organic matter.
The EXO sondes carry Smart QC, which is a series of quality control checks that run automatically to help maintain calibration. Feedback from testing has confirmed that the checks cut down on wasted trips into the field due to setup or configuration errors.Read More