COULOMETRIC SENSING
FAST-RESPONSE, TRACE AND ULTRA-TRACE OXYGEN MEASUREMENTS
Servomex’s high-purity oxygen
(O 2 ) analyzers are built around
non-depleting Hummingbird
Coulometric sensor technology.
to reach the extremely low levels
demanded by electronics-grade
gas quality control.
These industry-proven sensors
enable direct measurements
at trace and ultra-trace levels,
without needing periodic
replacement or producing the
false low readings associated
with traditional fuel cell sensors.
While Paramagnetic and Zirconia
solutions are highly effective for
percentage O 2 measurements, an
electrochemical sensor is required
The electrolyte solution contains
potassium hydroxide (KOH), which
assists in the migration of OH- to
the high-purity, non-carbon anode.
The ions are oxidized at the anode,
completing the reaction. The
reduction and oxidation reactions
The analyzer then displays the O 2
content in parts-per-million (ppm)
or parts-per-billion units (ppb).
O 2
LASTS
5-10 YEARS
LONGER
THAN AN
ELECTROCHEMICAL
SENSOR
GAS SAMPLE
CARBON CATHODE
40H -
NON DEPLETING
PROPRIETARY ANODE
O 2 + 2H 2 O + 4e -
4OH - (cathode)
-
4OH
O 2 + 2H 2 O + 4e - (anode)
Components of a Coulometric sensor
P04
10
6.
5m
m
mm
96.5
Servomex's Coulometric sensor
ACID GAS TOLERANCE
RAPID
RESPONSE
Our sensors work on a simple
Coulometric process. The sample
gas is in direct contact with the
sensor cathode. Any O 2 present is
reduced to hydroxyl ions (OH-).
are both driven by a voltage of
approximately 1.3V DC, which is
applied to the sensor electrodes.
The current flow that results
from the reaction is proportional
to the O 2 concentration in the
sample gas. This provides a direct
O 2 measurement, eliminating
the errors that inevitably
result from indirect
measurement technologies.
Servomex’s Coulometric sensor also provides a very
fast response to changes in O 2 concentrations. For
example, if a sensor operating in the 0-1,000ppm
range is exposed to air, it is able to recover less than
a minute and measure <10ppm of oxygen in pure
nitrogen. This is highly beneficial for users who
deal with upset-prone applications. The sensor’s
performance is unaffected by reasonable changes
in flow rate and, because it is non-depleting
when exposed to O 2 , it has a longer lifespan than
electrochemical sensors.
When a traditional electrochemical sensor cell
fails, it must be thrown away and replaced. The
electrolyte in Servomex’s Coulometric cell can
be topped up for continued use. This means a
Coulometric sensor generally lasts between 5-10
years, much longer than the 12 months typical of a
regular electrochemical sensor.
Coulometric sensing from Servomex provides highly
sensitive O 2 measurements, and can be optimized to
reach an industry-leading Lower Detection Limit of 45
parts per trillion. It can handle both flammable and
non-flammable samples, providing an advantage over
Zirconia technology, which offers ppm measurements
but only works with non-flammable samples.
TRACE & ULTRA TRACE
MEASUREMENT
SENSOR PERFORMANCE
Technology:
Accuracy: < ±3% reading or < ±0.05% of range,
whichever is greater
Zero drift: Negligible
Response time: T 90 < 30 seconds
Time to reading: < 5 seconds*
* Under constant conditions.
Allow at least 24 hours for electrode equalization when starting from ambient conditions.
PHYSICAL
Weight (transport): 500g
Weight (operating): 650g
Dimensions: 149mm x 96.5mm x 106.5mm
P05