General Principle Of Operation; Figure 1 - Light Transmission; Figure 2 - O Quenching Intensity Vs Time; Figure 3 - O Quenching Ac Modulation - Ametek OXYvisor Installation, Operation & Maintenance Manual

Installation, Operation & Maintenance Manual
OXYvisor Optical Oxygen Analyzer

2.5 General principle of operation

The OXYvisor analyzer uses a quench fluorescence technique with a sensor optically isolated from the
process, using the absorbency as a diagnostic function and analyzing the phase angle for measurement of the
analyte, oxygen, in the modulated time domain. This gives the analyzer the ability to measure accurately and
precisely under various and changing ambient and process conditions.
The analyzer uses an LED to emit blue light through fiber optic cable down to the luminophore which resides
at the sensor tip [Fig 1]. The luminophore absorbs the energy and rises to an excited state indicated by red
light returned back through the fiber optic cable. The properties of the emitted light are measured through a
photomultiplier tube back at the spectrometer within the analyzer.
In the absence of oxygen, the excited luminophore will fall back to its ground state at a specific intensity
and phase angle. When oxygen is present it quenches the fluorescence at a lower rate proportional to the
oxygen concentration [Fig 2.]. The phase shift and intensity differences between the excitation source and the
fluorescent signal is measured and the oxygen concentration is calculated [Fig 3].
The resulting measurement is specific to oxygen concentration. The luminophore is unaffected by other
constituent gases and flow rate. The measurement is applicable in both gas and liquid phase. Temperature
compensation is required to account for quenching efficiency at different temperatures and pressure
compensation is required to measure at process pressured different than the pressure at time of calibration.
Light transmission through fiber optic to luminophore
Oxygen sensitive luminophore
exposed to the process liquid

Figure 1 - Light Transmission

Fiber optics transmits light
and receives emitted light
back from the luminophore
O
2
O
O
2
2 O
2
Effects of 100 ppm oxygen quenching
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0 5 10 15
Time (µseconds)
Figure 2 - O Quenching Intensity vs Time
2
AC modulation and the phase shifted output
reference
1.0
signal
0.9
ϕ
0.8
1
0.7
0.6
0.5
0.4
ϕ
0.3
2
0.2
0.1
0
-5 0 5 10 15
Time (µseconds)
Figure 3 - O Quenching AC Modulation
2
Section 2
Technical Product Specification
The effect of O2
quenching on light
intensity from the
0% Oxygen luminophore sensor is
100 ppm Oxygen
shown above. Light
emitted from the
excited luminophore
has higher intensity
over a longer period
than when oxygen is
present. The intensity
and time are measured
by the spectrometer
withing the OXYvisor
20 25
to provide an oxygen
measurement.
AC modulation of the
blue light results in a
similar waveform of the
emitted red light from
the luminophore sensor.
The presence of oxygen
causes a phase shift
between Փ1 and Փ2 of
the red light waveform.
Measurement of
this phase shift
proportionally matches
the loss of intensity
shown in Fig 2 above.
measuring
The combination of
signal
both measurement
techniques provides a
stable, accurate method
20 25 30
to measure oxygen in
liquid and gas phase
applications.
15