Fluid Flow Meters

Reference data and engineering information about fluid flow meters for process control applications.

fluidflowmeters

Overview

Engineering reference data for Fluid Flow Meters in process control.

Key Formulas

PID Controller

$u(t) = K_p e(t) + K_i \int e(t)dt + K_d \frac{de}{dt}$

Proportional-Integral-Derivative control.

Transfer Function

$G(s) = \frac{K}{\tau s + 1}$

First-order system.

Variables

Symbol	Description	Unit
$K_p$	Proportional gain	—
$K_i$	Integral gain	1/s
$K_d$	Derivative gain	s
$\tau$	Time constant	s

Flowmeter Type Comparison

The extracted content references a wide variety of flow measurement technologies. Below is a comparison of key principles and typical characteristics for common types.

Flowmeter Type	Primary Principle	Typical Accuracy	Key Advantage	Common Application
Orifice Plate	Differential Pressure (Bernoulli)	±1-2% of full scale	Low cost, simple, no moving parts	General industrial gas/liquid flow
Venturi Tube	Differential Pressure (Bernoulli)	±1% of reading	Low permanent pressure loss, high accuracy	High-flow, low-loss applications
Pitot Tube	Differential Pressure (Bernoulli)	±1-5% of reading	Minimal flow obstruction, measures velocity profile	Air flow, clean gas, ducts
Ultrasonic (Time-of-Flight)	Transit Time Difference	±1-2% of reading	Non-invasive, no pressure loss, bidirectional	Large pipes, water, flare gas
Ultrasonic (Doppler)	Doppler Frequency Shift	±2-5% of reading	Works on dirty fluids with particles/bubbles	Wastewater, slurry, aerated liquids
Electromagnetic	Faraday’s Law of Induction	±0.5-1% of reading	No moving parts, handles dirty/corrosive fluids	Water, wastewater, slurries
Coriolis Mass	Tube Vibration & Coriolis Force	±0.1-0.5% of reading	Direct mass flow measurement, high accuracy	Custody transfer, chemical dosing
Vortex	Von Kármán Vortex Street	±1% of reading	No moving parts, good rangeability	Steam, clean gases, general liquids
Turbine	Rotor Speed vs. Flow Velocity	±0.5-1% of reading	High accuracy, good rangeability	Petroleum, hydrocarbon liquids
Positive Displacement	Volumetric Trapping of Discrete Volumes	±0.1-0.5% of reading	High accuracy at low flow, no straight runs	Fuel oil, viscous fluids, batching
Variable Area (Rotameter)	Float Position vs. Flow Rate	±2-5% of reading	Simple, visual indication, low cost	Low-flow lab, gas sampling

Source: General engineering principles, derived from referenced flowmeter comparisons.

Key Measurement Principles

The text highlights several foundational concepts for understanding flow measurement:

Bernoulli's Equation: Governs the relationship between pressure, velocity, and elevation in a flowing fluid. It is the fundamental principle behind orifice, venturi, nozzle, and pitot tube meters.
Velocity-Area Principle: Flow rate is calculated as the product of the cross-sectional area of a conduit and the average fluid velocity. This is critical for open channel measurement (weirs, flumes) and velocity-profiler meters.
Vortex Shedding Frequency: For vortex flowmeters, the frequency of vortices shed from a bluff body is directly proportional to the volumetric flow rate.
Doppler Effect: For ultrasonic Doppler meters, the frequency shift of an ultrasonic wave reflected off moving particles or bubbles is proportional to the fluid velocity.
Time-of-Flight (Transit Time): For ultrasonic time-of-travel meters, the difference in propagation time of ultrasonic pulses sent with and against the flow is proportional to the fluid velocity.

References

Original Source

Source: engineeringtoolbox.com