CRFS Study Force Pressure Flow Volume Force Pressure

CRFS Study Force, Pressure, Flow & Volume

Force & Pressure • • • Mechanical Strain Gauge Piezo-resistive Capacitive Inductive Optical

Mechanical Gauges • Manometers • Force summing devices

Strain Gauge • Wire or foil which thins when stretched • Resistance increases when stretched • Usually used in pairs or groups of 4

Wheatstone Bridge Circuit • Diaphragm flex stretches some & compresses others • Increases sensitivity & linearity • Full or half bridge

Piezo-resistive • Semiconductor chip • Resistance changes when flexed • May include amplifiers

Capacitive • Capacitance between diaphagm & 1 or 2 fixed plates • Requires AC • Limited by characteristics of gap contents

Inductive • Inductance changes produced by metal diaphragm on 2 fixed coils • Requires AC

Optical • Light intensity varies with pressure

Pressure • Absolute Gauge Differential

Flow • • Fleisch pneumotach Screen pneumotach Pitot tube Venturi / Orifice Rotating vane Mass Flow Ultrasonic Differentiation of volume

Reynold’s Number • vs - mean fluid velocity, • L - characteristic length (equal to diameter 2 r if a crosssection is circular), • μ - (absolute) dynamic fluid viscosity, • ν - kinematic fluid viscosity: ν = μ / ρ, • ρ - fluid density.

Fleisch pneumotach • Resistive • Linear

Screen pneumotach • Resistive • Linear

Pitot tube • Bernoulli equation

Venturi / Orifice • Bernoulli equation

Rotating vane • Rotating air stream • Low inertia follower • Digital counter based

Mass Flow • Thermal

Ultrasonic • Doppler effect • Accurate timing

Differentiation of volume • Direct volume measurement • Rate of change

Volume • • Watersealed Rolling seal Bellows Gasometer