Brief explanation of the science behind pressure calibration.

1. Pressure Measurement
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2. Pneumatics & Hydraulics

Pneumatics is the study of the mechanical
properties of gases. Gases can be
compressed and stored to form potential
energy.

Hydraulics is the study of fluid mechanics.
Liquids can not be compressed so they are
well suited to perform heavily loaded tasks at
a distance when gases would just further
compress.
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3. Why Measure Pressure?

Process Controls

Room Differential (Isolation)

Movement in Explosive Environments

Hydraulics (Presses & Stamping)

Package Integrity (leak testing)
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4. SI Units

The pascal (Pa) is the SI derived unit for
pressure = 1 N/m2

That's about ¼ Lb spread out across a square
meter

The most common unit used in the US is the
PSI

That's 1 Lb on 1 square inch

It takes 6,895 Pascals to make 1 PSI
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5. Pressure Units

Pascal (Pa) InHg

Bar Atm (Atmosphere)

PSI Kg/cm2
 InH20 kPa
 cmH20 MPa
 ftH20 mmHg

Torr www.alliancecalibration.com

6. Manometer
The simplest device
used to measure
pressure is the
manometer. A “U”
shaped tube filled with
water. This is the
origin of the unit
“Inches of Water
Column”
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7. Pressure Gage
When pressure
increases in a
curved flattened
tube the tube
straightens
This is referred to
as a “Bourdon
Tube Gage”
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8. Pressure Transducer
An electronic strain gage is
attached to a diaphragm.
When pressure is applied to
the diaphragm the strain gage
registers the force applied
and then “Calibration Factors”
are used to interpret the force
as pressure
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9. Accuracy

Typically electronic devices have a
specification based on % reading however...

“Most” pressure measuring instruments have
an accuracy based on % of full scale of the
device.

This is important to keep in mind because a
10,000 PSI digital gage will read out to 1 PSI,
but at 1%FS it has an accuracy of ±100 PSI
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10. Calibration
Direct Comparison

The UUT and Standard a both connected to a
single pressure source and the readings are
compared
Primary Standards

Deadweight Testers are also common and
apply pressure to a UUT based on the
quantities of: length, mass and time.
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