Xylem EXO Series User Manual

pg | 17
2.9
Dissolved Oxygen
Sensor Overview
e 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. e 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. e 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. us,
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 quantied by the Stern-Volmer equation.
For most lifetime-based optical DO sensors, this Stern-
Volmer relationship
((Tzero/T) – 1) versus O
2
pressure
is not strictly linear (particularly at higher oxygen
pressures) and the data must be processed using analysis by
1.7
(continued)
Sensor Cap
Sensor without
Sensor Cap
Specifications
Units
% Saturation, mg/L
Temperature
Operating
Storage
-5 to
+
50°C
-20 to
+
80°C
Range
0 to 500% air sat.
0 to 50 mg/L
Accuracy
0-200%: ±1% reading or 1%
air sat., whichever is greater;
200-500%: ±5% reading
0-20 mg/L: ±1% of reading or
0.1 mg/L;
20-50 mg/L: ±5% reading
Response
T63<5 sec
(see pg 12)
Resolution
0.1% air sat.
0.01 mg/L
Sensor Type
Optical, luminescence lifetime
599100,
599110

Xylem EXO Series Specifications

General

Brand	Xylem
Model	EXO Series
Category	Measuring Instruments
Language	English