(55) Accurate Pressure Measurement
07-05-2020, 12:14 PM
Post: #1 SlideRule Senior Member Posts: 1,229 Joined: Dec 2013
(55) Accurate Pressure Measurement
An extract from An Investigation Into the Required Equipment and Procedures for the Accurate Measurement of Pressure in Hydraulic Fluid Power Systems, The Fluid Power Institute (Milwaukee School of Engineering), AD-A244 165 (U.S.AR. M&E-R&R), May 1976, 139 pgs.
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1.2.1.3.1 Snubber Equation Derivation
Using the laboratory data obtained in Section 1.2.1.1, characteristic equations for various degrees of snubbing (i.e., 20°, 25°, and 10°), were obtained.
The P-Q characteristic, in general, for the orifice can be shown to be the following:

The above equation closely resembles the equation of a straight line:

A simple least-squares curvefit can now be employed to determine n and log₁₀ K. Actual calculations for these values were performed using HP-55 programmable calculator and the program given below … page 22

1.2.1.3.2 Hydlraulic Gauge Capacitance Equation
It can be shown that the pressure-volume relationship for the bourdon tube pressure gauge is:

The hydraulic capacitance is defined as the rate of change of volume with respect to pressure. That is,

Applying the derivative to the original equation gives

Rearrangement of the above equation results in:

which resembles the equation of a straight line

The calculations necessary to obtain the least-square's fit were again performed on a programable HP-55 calculator using the program below … page 22
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