SERVOMEX
TECHNOLOGY FOCUS
PLASMA SENSING – FOR STABLE
MEASUREMENT OF UHP GASES
In the field of Gas Chromatography,
many sensors are available that cover
a broad range of measurements. Each
sensor has advantages and drawbacks,
so a solid understanding of the different
technologies is important.
Challenged to find a safer alternative to
the FID, Servomex’s R&D team undertook
extensive research on Servomex’s
existing Plasma Emission Detector (PED)
technology, aiming to improve the
technology’s sensitivity and identify a
configuration specific to hydrocarbons,
while avoiding the use of explosive gases.
Their intensive research led to the
development of a PED sensor optimized for
the trace-level analysis of hydrocarbons.
SERVOPRO NanoChrome -
POWERED BY PED
The PED sensor is at the heart of the
SERVOPRO NanoChrome analyzer,
designed to measure ultra-trace levels of
impurities in electronic gases.
Offering the most stable P-Gas analysis on
the market, even at the lowest levels, the
NanoChrome delivers a superb sub-ppb
measurement of the contaminant gases and
hydrocarbons that can be present at ultra-
trace levels in semiconductor manufacture.
Download the NanoChrome brochure today:
servomex.expert/nanochrome-brochure
Thermal Conductivity Detector (TCD) and
Flame Ionization Detector (FID) sensors
are long-established and are the most
widely used measurement technologies.
However, a more recent technological
development has surpassed their
performance, especially when ultra-trace
level measurement is required.
PED SENSITIVITY TO
CH 4 , CO 2 AND NMHC
WITH NanoChrome
A chromatogram obtained with a PED
sensor at 5ppb for CH 4 , CO 2 and NMHC.
This chromatogram shows clear sensitivity
to hydrocarbons, as well as sensitivity
to CO 2 achieved without the use of a
methanizer which converts CO and CO 2
to CH 4 . While a methanizer is always
required to measure CO and CO 2 with
a FID sensor, it is not required by the
PED – improving measurement reliability,
avoiding catalyst poisoning risks
associated with methanizers and creating
a further reduction in cost of ownership.
FID technology is commonly used for
hydrocarbons analysis, being relatively
simple to use and offering a very sensitive,
selective and linear measurement.
However, this sensor type uses a flame
to burn hydrocarbons, which requires air
and hydrocarbon-free hydrogen fuel gas.
Increasingly stringent health and safety
requirements means concerns over using
flammable pure hydrogen have been
raised by users.
Gas Chromatography is used for a wide range of applications
ADVANTAGES OF PLASMA EMISSION DETECTOR TECHNOLOGY
The Servomex PED sensor offers many
advantages over FID technology. It is very
sensitive and selective to any molecules
containing carbons (organic or inorganic),
being up to 100 times more sensitive than
a FID measurement, depending on the
carrier gas.
FID sensors are traditionally renowned
for sensitivity, with the best FID sensors
offering a detection limit between
10 parts per billion (ppb) and 20ppb
methane equivalent. This limitation is
due to the FID sensor requiring carrier
gas, fuel and air to operate, making the
sensor more prone to noise from low-
level hydrocarbon contamination from
those three potential sources.
Hydrocarbons contained in any of
these gases are ionized by the sensor,
P08
causing drift and noise which limits
reliable performance for ultra-trace level
measurements.
This level of detection is usually acceptable
for General Gas (G-Gas) made before
the main purifier, which requires a lower
detection limit (LDL) of about 10ppb.
However, the Pure Gas (P-Gas), used inside
the fab after the purifier stage, has much
lower LDL requirements of 1ppb or less.
As the PED sensor requires only a carrier
gas, external contamination from air
and fuel is removed. While it is still very
important to have a clean carrier gas,
techniques exist to obtain a clean helium
or argon carrier gas with a total impurity
level below 1ppb. In addition, avoiding
the use of hydrogen and air reduces cost
ENSURE A FULL LIFETIME OF PERFORMANCE
NEW PED SENSITIVITY
STEP CHANGE
of ownership, as less gas is consumed and
fewer purification systems are required.
A step response using a NanoChrome
analyzer at ppb level, again showing the
sensitivity achieved with this sensor. The
achievable limit of detection for CO, CO 2 ,
CH 4 and NMHC is below 1ppb.
There are some limitations to using
PED technology. The sensitivity of the
measurement means it is suitable only for
trace analysis applications (<1000 parts per
million). Due to the nature of the plasma,
the sensor also exhibits some occasional
mild cross-interferences due to the sample
matrix, which requires more demanding
chromatographic methods – also
sometimes the case with FID technology.
Overall, however, the PED sensor
revolutionizes the analysis of
hydrocarbons, CO and CO 2 , improving
measurement sensitivity, successfully
addressing the safety concerns associated
with the use of hydrogen and reducing
the cost of ownership.
Visit
servomex.expert/service
or contact your local business center today
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