The Science behind Pressure Calibration: The Basics

Pressure Measurement

www.alliancecalibration.com

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.


Why Measure Pressure?

Process Controls Room Differential (Isolation) Movement in Explosive Environments Hydraulics (Presses & Stamping) Package Integrity (leak testing)


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


Pressure Units

Pascal (Pa) Bar PSI InH

20

cmH20

ftH20

Torr

InHg

Atm (Atmosphere)

Kg/cm2

kPa

MPa

mmHg


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”


Pressure Gage

When pressure increases in a curved flattened tube the tube straightens

This is referred to as a “Bourdon Tube Gage”


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


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


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.


The Science behind Pressure Calibration: The Basics

Business

Transcript of The Science behind Pressure Calibration: The Basics