Fluke and Transcat present a webinar on how to overcome challenges in performing pressure calibrations in the field or in the shop.

1. In the Field or in the Shop: Overcoming
the Challenges in Pressure Calibration
Presenter: Tim Francis, Fluke Calibration
Principles and practical tips about electrical, flow, pressure,
RF and temperature calibration

2. Agenda
• The Vocabulary – Definition of some basic terms
– Reference Mode – Gauge versus absolute versus
differential
– Pressure Ranges – How high is high and how low is
low?
• Challenges and how to overcome them
– Safety Considerations
– Environmental Impact
– Contamination
– The right process and equipment for the job
• Question and Answer
©2016 Fluke Corporation.

3. Agenda
• The Vocabulary – Definition of some basic terms
– Reference Mode – Gauge versus absolute versus
differential
– Pressure Ranges – How high is high and how low is
low?
• Challenges and how to overcome them
– Safety Considerations
– Environmental Impact
– Contamination
– The right process and equipment for the job
• Question and Answer
©2016 Fluke Corporation.

4. Reference Modes
• Pressure values are sometimes followed by the words
“gauge” or “absolute” (or possibly “psig” or “psia”)
• What do these words mean and how do they affect the
calibration process?
• Measurements are relative
– You don’t say, “I live 5 miles.” You say, “I live 5 miles from
here” or “I live “5 miles from my work.” Everything has a
starting point.
– Pressure is no different. Saying “The pressure is 5 psi”
doesn’t say the whole story. More proper to say “The
pressure is 5 psi above atmosphere.”
– Gauge, absolute, and differential are simply shorthand for
this.
©2016 Fluke Corporation.

5. Gauge Mode
• Referenced to atmospheric
pressure
– 0 means that your test
pressure is the same as
atmosphere
– Most common reference mode
– Can be both positive and
negative (partial vacuum)
– Usually the easiest to measure
• Examples
– Tire Pressure
– Many Process Measurements
Gauge (+ or -)
Barometric
Zero pressure, no molecules
©2016 Fluke Corporation.

6. Absolute Mode
• Referenced to a perfect vacuum
– 0 means that it is a perfect
vacuum (absolutely no
molecules)
– Can only be positive numbers –
You can’t have negative
molecules in a vessel
– More difficult measurement –
How do you re-zero the
reference?
• Examples
– Barometric pressure
measurement
– Airplane altitude measurement
– Downhole tools
Gauge (+ or -)
Absolute
Barometric
Zero pressure, no molecules
©2016 Fluke Corporation.

7. Differential Mode
• Referenced to another pressure (line
pressure)
– 0 means that there is no difference in the
two pressures
– Gauge mode can be thought of as a
special case of differential mode.
– Can be a difficult measurement to make.
Few calibrators support high line pressure.
– Can be both positive or negative (above or
below line pressure)
• Examples
– Flow measurements in a pipeline
– Draft Range measurements – difference in
pressure between two rooms
Gauge (+ or -)
Absolute
Differential
Barometric
Zero pressure, no molecules
©2016 Fluke Corporation.

8. How high is high and low is low?
• Pressure measurement covers a wide range, from
vacuum to > 60,000 psi
– Vacuum – Less than atmosphere
– Draft Range – low differential/gauge pressures (< 2 psi)
– Low Pressure – Normally pneumatic pressures (<= 300 psi)
– Medium Pressure – Could be pneumatic or hydraulic (<=
2000 psi)
– High Pressure – Almost always hydraulic (2000 psi to
20,000 psi)
– Very High Pressure - > 20,000 psi
• General statements – no official rules
©2016 Fluke Corporation.

9. Challenges created by Reference Mode
• I only have a gauge standard. Can I use it to
calibrate an absolute device?
• The spec sheet says that the range is -15 to 30
psi, but I can’t get down to -15. Why not?
• Is it okay to calibrate a differential device as
though it was a gauge mode device?
• What is sealed gauge and when can I use it?
©2016 Fluke Corporation.

10. Using a gauge standard to measure absolute mode
• There will be an offset equal to barometric pressure
(~14.7 psi)
• The offset will change with barometric pressure – if
there is a storm that causes barometric pressure to
drop 0.4 psi, then your error will change by 0.4 psi.
• If working with high pressures, you may be able to
estimate barometric pressure and add it to your
standard reading.
• If working with lower pressures, you will need to
measure barometric pressure and continuously adjust
your standard reading to compensate.
©2016 Fluke Corporation.

11. -15 psi isn’t reachable
• At barometric pressure, 0 psi gauge = ~14.7 psi
absolute.
• -15 psi gauge = -0.3 psi absolute – NOT POSSIBLE
• The lowest you can possibly go is -1 x barometric
pressure
– Denver, Colorado = ~12.1 psi absolute
– Honolulu, Hawaii (at the beach) = ~14.7 psi absolute
– Mauna Kea, Hawaii = ~8.7 psi absolute
• Even at sea level, it may not be possible to get all
the way to -14.7 psi – you have to get all the
molecules out.
©2016 Fluke Corporation.

12. Calibrating High Line Differential
• Example: Pressure transmitter is used on a
pipeline that has a pressure of ~1500 psi
absolute. It’s measuring the drop in pressure
across an orifice, ~30 psi.
• To calibrate it like it is used, we need to apply
1500 psi to one side of the transmitter and 1530
psi to the other side.
• Difficult to do, so we normally leave one side
open to atmosphere and apply 30 psi to the other
side.
• Is this acceptable? Depends on who you ask.
©2016 Fluke Corporation.

13. Sealed Gauge
• Special case that is a hybrid of gauge mode and
absolute mode
• If the test port is open to atmosphere, it reads 0 (like
gauge mode)
• If test port is open to atmosphere and barometric
pressure changes, then the measurement will change
with it (like absolute mode)
• Similar to using an absolute mode device and
subtracting a default barometric pressure value from it.
• Useful for high pressure applications where variations
in barometric pressure
©2016 Fluke Corporation.

14. Agenda
• The Vocabulary – Definition of some basic terms
– Reference Mode – Gauge versus absolute versus
differential
– Pressure Ranges – How high is high and how low is
low?
• Challenges and how to overcome them
– Safety Considerations
– Environmental Impact
– Contamination
– The right process and equipment for the job
• Question and Answer
©2016 Fluke Corporation.

15. Safety Considerations
• A pressurized vessel has some inherent safety risks
• Make sure all equipment is rated to the proper
pressures for the work being performed.
– Some shops only stock pressure lines and fittings that are
rated to the highest pressure they work to. This works if
the highest pressure is relatively low. Doesn’t work if the
highest pressure is 10,000 psi or higher.
• Use the proper Personal Protection Equipment (PPE)
• When working in the field, be cognizant of other
dangers around you.
©2016 Fluke Corporation.

16. Impacts from the Environment
• A pressure calibration can be impacted by the environment around it.
• Temperature – Almost everything that measures pressure is also
impacted by temperature. Pressure Calibrator manufacturers will
characterize and compensate, but they still perform best over a given
temperature range.
• Gravity – Acceleration of gravity varies by location. A traditional
deadweight tester is impacted by this.
• Head height – A large difference in elevation between the reference
and the device under test will create an error
– 3 feet in gas = ~0.01% reading
– 3 feet in oil = ~ 10 psi
• Large drafts, temperature swings, or changes in barometric pressure
can make it difficult to get pressure to stabilize
©2016 Fluke Corporation.

17. Contamination
• Dirt, debris, and liquids from the
Device Under Test can cause problems:
– Damage your calibration equipment
– Cross contaminate other Devices Under
Test
• How do we combat it?
– Clean the devices before we connect to
them
– Make use of filters, traps, or separators

18. In the field or in the lab?
• Need to consider a few questions
– Can the work be done safely in the field?
– Does the environment allow for the calibration to
be done properly?
• Is the temperature stable and within the allowed for
operating range of the standard?
• If you are using a deadweight tester, do you know the
local gravity sufficiently?
• Can you easily connect to the device? Or is it better to
calibrate a similar device in the shop and rotate it into
the field?
©2016 Fluke Corporation.

19. The Right Equipment
• Portable versus Bench
– Portable type instruments, like the Fluke
718 can be used on the bench, but…
– They are designed for the field, so they
aren’t always ergonomic for the bench.
©2016 Fluke Corporation.
• Make sure you have devices that cover
the proper range and mode
– Add pressure modules for absolute mode
– Not always appropriate to calibrate low
pressure with a higher range instrument
– Example: Fluke 3130 with 750P Pressure
Modules

20. Conclusion
Pressure calibrations can be challenging, but
these challenges can be overcome with the right
processes and the right equipment.
©2016 Fluke Corporation.

21. Special limited-time offer!
• Gift with purchase – up to $1200 value
• +Go to www.transcat.com/deals for more
details

22. Questions or Comments?
Email the moderator, Nicole VanWert:
nvanwert@Transcat.com
Transcat: 800-828-1470
www.Transcat.com
For related product information, go to:
www.Transcat.com/Fluke