# 04 Hydraulic Deadweight Testers-09-24-2015 - Calibration of...

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Calibration of Pressure Gauge by a Dead Weight Tester 1. 0 GENERALINFORMATION Deadweight Testers are the primary standards for pressure measurement. Utilizing the well-proven Piston/Gauge system, consisting of a vertically mounted precision lapped Piston and Cylinder assembly, accurately calibrated weight masses (FORCE) are loaded on the Piston (AREA) which rises freely within its Cylinder. These weights balance the upward force created by the pressure within the system. PRESSURE = FORCE/AREA Each weight is marked with the Tester serial number and the pressure measured when placed on a correctly spinning and floating Piston. The total pressure measured is the summation of the weights plus the Piston Weight Carrier. The Deadweight Tester has been calibrated to the Gravity, Temperature and Air Density stated on the Certificate. Equations and factors are given on the Certificate to adjust for any variations in these environmental conditions. Gravity varies greatly with geographic location and so will the Deadweight Tester reading. Due to the significant change in gravity throughout the world (0.5%), ensure that the Tester has either been manufactured to your local gravity or that you have applied the correction from the calibrated gravity. Example: Deadweight Tester calibrated gravity: 980.665 cm/s 2 (980.665 cm/s 2 is the International Standard Gravity) Gravity at site: 981.235 cm/s 2 Indicated Pressure: 250 psi True Pressure : (981.235 x 250)/980.665 =1.0005812 X 250 =250.1453 psi Temperature and Air Density variations are less significant than Gravity. Variations should be corrected for when maximum accuracy is required. Temperature variation example: Deadweight Tester calibrated temperature: 20 o C

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Operating temperature : 24 o C Percentage change per' o C : 0.002% Indicated Pressure : 250psi True Pressure: 250+ (20-24)*0.002/100)*250= 249.98 psi The pressure measured is at the top of the Test Station Seal. Vertical height difference between this datum line and the connection to the instrument under test should be corrected for. To correct for vertical heights above and below
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• Fall '16
• Chen-wei shin

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