The Science behind Pressure Calibration: The Basics
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This document discusses pressure measurement. It explains that pneumatics and hydraulics involve the study of gases and liquids under pressure. Pressure is measured for process control, isolation, movement in explosive environments, hydraulics applications, and package integrity testing. The most common pressure units are pascals, bars, PSI, inches of water, and torr. Simple pressure measurement devices include manometers and bourdon tube gages, while transducers convert pressure to electrical signals. Accuracy depends on percentage of full scale. Calibration involves direct comparison to a pressure standard or deadweight tester.
The Science behind Pressure Calibration: The Basics
- 1. Pressure Measurement www.alliancecalibration.com
- 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. www.alliancecalibration.com
- 3. Why Measure Pressure? Process Controls Room Differential (Isolation) Movement in Explosive Environments Hydraulics (Presses & Stamping) Package Integrity (leak testing) www.alliancecalibration.com
- 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 www.alliancecalibration.com
- 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” www.alliancecalibration.com
- 7. Pressure Gage When pressure increases in a curved flattened tube the tube straightens This is referred to as a “Bourdon Tube Gage” www.alliancecalibration.com
- 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 www.alliancecalibration.com
- 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 www.alliancecalibration.com
- 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. www.alliancecalibration.com