Pressure gauges are either direct- or indirect-reading.Hydrostatic and elastic gauges measure pressure are directly influenced byforce exerted on the surface by incident particle flux, and are called directreading gauges. Thermal and ionization gauges read pressure indirectly bymeasuring a gas property that changes in a predictable manner with gas density.Indirect measurements are susceptible to more errors than direct measurements.
§ Dead-weight tester
§ mass spec +ionization
Dynamic transients ]
When fluid flows are not in equilibrium, local pressures may behigher or lower than the average pressure in a medium. These disturbancespropagate from their source as longitudinal pressure variations along the pathof propagation. This is also called sound. Sound pressure is the instantaneouslocal pressure deviation from the average pressure caused by a sound wave.Sound pressure can be measured using a microphone in air and a hydrophone in water. Theeffective sound pressure is the root mean squareof the instantaneous sound pressure over a given interval of time. Soundpressures are normally small and are often expressed in units of microbar.
§ frequency response ofpressure sensors
The American Society of Mechanical Engineers (ASME) has developedtwo separate and distinct standards on pressure Measurement, B40.100 and PTC19.2. B40.100 provides guidelines on Pressure Indicated Dial Type and PressureDigital Indicating Gauges, Diaphragm Seals, Snubbers, and Pressure LimiterValves. PTC 19.2 provides instructions and guidance for the accuratedetermination of pressure values in support of the ASME Performance Test Codes.The choice of method, instruments, required calculations, and corrections to beapplied depends on the purpose of the measurement, the allowable uncertainty,and the characteristics of the equipment being tested. The methods for pressuremeasurement and the protocols used for data transmission are also provides.Guidance is given for setting up the instrumentation and determining theuncertainty of the measurement. Information regarding the instrument type,design,
applicable pressure range, accuracy, output, and relative cost isprovided. Information is also provided on pressure-measuring devices that areused in field environments i.e., Piston Gauges, Manometers, and
Low-Absolute-Pressure (Vacuum) Instruments. These methods aredesigned to assist in the evaluation of measurement uncertainty based oncurrent technology and engineering knowledge, taking into account publishedinstrumentation specifications and measurement and application techniques. ThisSupplement provides guidance in the use of methods to establish thepressure-measurement uncertainty.