Rosemount Gas Analysis
Frequently Asked Questions (FAQs)
GC Webinar Series
February 11, 2016
Maximizing Your GC's Capabilities
Validating the Operation of Your Gas Chromatograph
Emerson recently hosted the webinar "Validating the Operation of Your Gas Chromatograph". These are the
questions asked by the audience members along with the answers provided by our subject matter experts.
■ Do you have a table for RF deviation for C9+?
The relative RFs vary with the GC model, kind of detector used and
ow path. We do not publish a relative response factor list.
■ What are the analytic sensitivity and method
detection limits?
The analytical sensitivity varies with GC, detector, concentration
of the component and temperature range. The rule of thumb
is that a Thermal Conductivity Detector (TCD) can be used to
detect components down to the 50 ppm concentration. There
are TCDs capable to detect limits down to 5 ppm. The rule of
thumb for a Flame Ionization Detector (FID) is that it can detect
concentrations from 1 Mole % to sub ppm.
■ Can a calibration gas be brought back to original
composition if the temperature of the bottle has
been accidently lowered below freezing?
If the bottle temperature has gone below its hydrocarbon dew
point so that the heavies have dropped out but the bottle has not
been open (has been in storage), then yes the calibration gas can
be brought back to the original composition. You want to heat
the bottle for a long time, at least overnight, at 30 degrees above
the gas' hydrocarbon dew point. If calibration gas has been taken
out of the bottle while it was cold, then the gas is ruin and the
calibration gas bottle should be replaced.
■ Should you ever have to force calibrate when
changing calibration standard bottle?
Yes, sometimes. The old calibration gas bottle has an uncertainty
in measurement, the new calibration gas bottle has an uncertainty
in measurement value and the GC has an uncertainty in
measurement. When you add up the uncertainties, the smaller
components may go outside the response factor alarm limit. This
does not happen frequently. If the old calibration bottle has been
there for awhile, the heavies may have dropped out and cause an
alarm when compared to the new calibration gas bottle. You also
get a bad calibration gas cylinder from the supplier despite the
certicate. When you do a force calibration, you should still check
the response factor order.
■ You said that running your calibration gas as an
unknown will not show issues, if i have a certificate
that says 2 % N2 and the unknown is coming up at
5 %, would this not indicate an issue?
Yes - this would indicate an issue. If you use the calibration gas
as an unknown and the analysis does not match the certicate,
you denitely got an issue. The issue with running the cal gas
as an unknown is that it can hid an issue such as cutting off a
component. Running the calibration gas as an unknown and
having the analysis match the certicate, does not mean the GC
is operating correctly.
■ Is there any plans to include some of these 370XA
features (ideal RF order and auto valve timing
adjustment) in future firmware upgrade for the
700XA?
Yes. For standard 700XA applications, we are looking at offering
auto-valve timing and other unique features currently only found
on the 370XA GC.
■ If Specific Gravity is not being analyzed, what
caused the number to change?
The Specic Gravity (SG) is a calculated value, not a measured
value. The GC provides a theoretical density of the gas sample.
If the analysis is incorrect, the SG that was calculated using the
analysis data will be incorrect.
Rosemount Gas Analysis
Frequently Asked Questions (FAQs)
GC Webinar Series
February 11, 2016
■ What is the lead time on GC analyzers?
The lead time on the Rosemount GCs vary with the GC model and
application. You would need to contact the factory for lead times
specic to your application and GC.
■ At what pressure should calibration gas be
changed out?
When the pressure in the calibration cylinder get to set point on
the regulator, the cylinder should be switched out. If the pressure
of the calibration cylinder gets too low, it is possible to get a
deviation alarm. The set point on the regulator depends on the GC
model.
■ Do all the validation procedures mentioned here
apply to the Process GCs as well?
Yes, denitely. The theory still applies. Relative response factors
will not be the same compared to C6+ as the concentrations will
be different
■ Can you store the calibration gas certificates in the
GC somehow for auditing?
Yes for XA Chromatographs (370XA, 700XA, and 1500XA). You
can upload and store various types of documents (Word, TXT,
PDF, Excel) into the GC memory to have a permanent record.
To upload and store a document on the GC, open MON2020,
connect to the GC. On the Menu Bar, click on Logs/Reports and
select Drawings/Documents.
■ When reading the specific gravity of an analysis,
what is that actually telling me about the gas
sample? Has there ever been a problem with an
analysis of specific gravity?
The Specic Gravity (SG) is a calculated value, not a measured
value. The GC provides a theoretical density of the gas sample.
If the analysis is incorrect, the SG that was calculated using the
analysis data will be incorrect.
Model 700 GCs can not be run with MON2020. Some of the
improvements of the MON2020 software over the MON2000
software include an administrator role, ability to view unlimited
number of chromatograms in any conguration, multiple users
being able to be connect to the same gas chromatograph
simultaneously and the ability to perform trend analysis. Along
with software improvements, there have been GC improvements
over the years. Newer GC models have smaller footprints, use less
carrier and calibration gases and are easier to maintain. If it has
been awhile since your GC was purchased, it may be cost-effective
to upgrade your GC and software.
■ Can you get the response factors' graphs in a
simple menu in the MON2020 software?
Yes. On the Menu Bar, click on Logs/Report, then click on
Molecular Wt. Vs Response Factor. It is available for XA
chromatographs (370XA, 700XA and 1500XA) although only
shows the normal hydrocarbons (C6+) because it is according to
GPA standards
■ What is the maximum RF % deviation that is
acceptable?
Rosemount sets the alarm at 10 % RF Deviation by default. The
value is a compromise between getting too many alarms and not
catching an issue with the GC early . Some customers set the alarm
limit as low as 5 %.
■ What is the expected range of deviation for RF
Deviation %?
The expected RF Deviation % is less than 10 %, with typical dayto-day variation expected to be less than 2 %. Most typical RF
Deviation on a day-to-day basis is 1 %. If you have a changed in the
atmospheric pressure, example a cold front coming through, you
may see a 2 % RF Deviation. Rosemount sets the alarm at 10 % RF
Deviation by default. Some customers set the alarm limit as low as
5 %.
■ Are there major benefits to upgrading from
MON2000 to MON2020?
One is not able to upgrade from MON2000 to MON2020 without
changing one's GC. The Model 700 and Model 500 operate on
MON2000 while the 370XA, 700XA and 1500XA operate on
MON2020. While MON2000 and MON2020 have a similar look
and feel, they are different software platforms. Model 500 and
NGC-FAQ-Webinar-Series-Maximizing-GC-Capabilities
■ Where does the ideal Response Factor (RF) ratio
and ideal RF deviation show up? Is it in MON2020?
The ideal Response Factors (RF) show up on the Calibration
Reports and the Component Data Table in MON2020. For the
370XA, the Calibration Report also shows the RF % Deviation from
Ideal.
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