In this presentation, you’ll learn about: • Physics principles that impact high-pressure calibration • Appropriate calibration tools • Different tips and techniques to simplify and improve the quality of high-pressure calibrations

1. Tips and Techniques for High-
Pressure Calibration

2. Agenda
• Basic vocabulary and the physics of pressure
• Special considerations when working with high pressure
• Equipment determination for high-pressure calibration

3. Definition of Pressure
• Pressure is a derived measurand. It uses the base
quantities, mass length and time.
P=F/A (Pounds per Square Inch)
• It is a state variable where the quantity values
describe the condition of a fluid much like
temperature.
• Most pressure measuring devices measure over a
range.
• Measurements are made in either some type of gas
or hydraulic fluid.

4. • No Strict Definition, it is a relative term – It depends on one’s
experience, the application and specific governing regulations
• For the scope of this discussion, we will consider pressures of
3000 psi (20 MPa) and above high pressure.
- Limit of many gas cylinders
- Common breakpoint for instrumentation
What is high pressure

5. Reference Mode
• 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.

6. 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

7. 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

8. 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

9. Head Pressure
• The weight of a column of fluid will generate a pressure
P = height X density X acceleration of gravity
• If the reference device and the device under test (DUT) are at different
vertical positions, the pressure at each of them will be different.
• With liquid, the density is constant with pressure, resulting in a constant
offset at all pressures
• With gas,
– the density increases with pressure (gas compresses). The error is a function of
the pressure.
– Gas is less dense than liquid, resulting in a smaller head height error
• Some calibrators will make the correction for you

10. PV=nRT
Where:
• P = Pressure
• V = Volume
• n = Number of fluid molecules (mass)
• T = Temperature
• R = Ideal Gas Constant
Understanding Pressure Stability

11. PV=nRT
Pressure is impacted by 3 things
• Number of fluid molecules
• Volume
• Temperature
Understanding Pressure Stability

12. Number of Molecules
• Keep leaks to a minimum
– Leads to instability
– Could possibly result in measurement
errors
• Method for generating pressure in a
gas system
– Push more molecules in the system to
increase the pressure
– Exhaust molecules out of the system to
decrease pressure

13. Volume Changes
• Inverse relationship – As volume
decreases, pressure increases
• As pressure increases, it pushes on
the inside of tubing and manifold
walls, causing the volume to
increase
– Causes the pressure to decrease
– May look like a leak
• Used to generate hydraulic
pressures using a “screw press” or
“variable volume”

14. Temperature
• In an enclosed system, temperature has the biggest impact on
pressure stability
• As pressure is increased, the temperature of the fluid also
increases.
• When the pressure set point is reached, the temperature
decreases, returning to ambient.
• This causes the pressure to decrease with it.
• Appearance of a leak, but the pressure drop will eventually
stabilize out

15. Considerations with High Pressure
• Safety
• Contamination
• Pressure Stability

16. Safety
• There are inherent danger with high pressure, but the risks can
be mitigated.
– Use Personal Protective Equipment (PPE)
– Ensure all pressure lines and fittings (and other components) are
properly rated for the application and are in proper working order
– Minimalize volumes where possible
– For highest pressures, consider using a liquid media

17. Contamination
• But there are drawbacks to using liquid as the media
• Leads to contamination of the DUT
• Liquid in the DUT can be different than the liquid in the
calibration system, contaminating the calibration system
• If contamination is a concern, a gas system might be preferable

18. Pressure Stability
• Pressure stability can be a bigger issue at higher pressures
• Temperature is more of an influence with liquids than gasses
• More expansion and contraction of pressure lines
• Can be minimized by using the appropriate equipment
– Gas devices will provide a more stable pressure
– Deadweight Testers provide stable pressures (the sinking piston acts
as a natural pressure regulator)

19. Equipment Determination
• Benchtop versus Portable
• Hydraulic versus Pneumatic
– Contamination Prevention
• Ease-of-use
– Physical effort
– Stability of pressure

20. Example – High Pressure Gas
• Fluke 700HPPK Pneumatic Pressure Pump
and Calibration Kit
• Can be combined with a Reference
Pressure Gauge
• Easy-to-use pump generates up to 3000
psi in 30 seconds
• Ideal for operation in the field, no
benchtop required

21. Example – High Pressure Liquid
• P3100 Hydraulic Deadweight Testers
• Dual Piston design covers a wide
pressure range in one instrument
• Floating piston provides a stable,
precise, and accurate pressure

22. Questions or Comments?
Email Nicole VanWert-Quinzi
nvanwert@Transcat.com
Transcat: 800-800-5001
www.Transcat.com
For related product information, go to:
www.Transcat.com/Fluke©2016 Fluke Calibration