data-acquisition.us

[daqmaster]

Here's what we'll cover in this tutorial:

Types of flow devices
Selecting a flow device
Basics of installation

[daqmaster]

Types of flow devices
Positive displacement
Differential pressure
Mechanical volumetric
Open Channel
Magnetic
Ultrasonic
Thermal
Fluidic
Mass flow

[daqmaster]

Positive displacement meters

Function by letting a known volume of fluid to pass through the meter
Very accurate (usually 1-1/2% of rate or better)
Can handle higher-viscosity materials (up to 20,000 centipoise)

[daqmaster]

Differential pressure flow meters

Function by sensing the differential across an orifice or flow restriction…the flow rate is proportional to the square root of the differential. The following was an example of an advanced differential pressure meter.

[daqmaster]

Mechanical volumetric flow meter

Function by converting rotational speed of a rotor (e.g. turbine) to turn a gear train or produce an electronic pulse
Accuracies vary: 5% of span to 1-1/2% of rate

[daqmaster]

Magnetic flow meters

Function on principles of Faraday’s law -- the most innately accurate volumetric flow meter
Varities include: flanged, wafer, and insertion styles, and also available for partially filled pipes

[daqmaster]

Ultrasonic flow meters

Function by: (a) measuring the transit time between two sensors or (b) doppler shift caused by the velocity of the solids-bearing liquid.

Normally supplied as clamp-on devices

[daqmaster]

Thermal flow meter

Functions via measuring the thermal dispersion caused by a moving fluid flowing past a heated temperature sensor
Ideal for use as a flow switch, normally 5% accurate

[daqmaster]

Fluid-based (aka "fluidic") flow meters

Function via forcing the fluid to oscillate in a detectable manner

Most common types: vortex shedding, and the various Coanda-effect flow meters

[daqmaster]

Mass flow flowmeters

Mass flow meters for liquids are generally coriolis-based devices
Gas mass flow meters operate by thermal dispersion
These meters read mass directly and, accordingly, flow and density is calculated

[daqmaster]

Open channel flowmeters

Function by measuring the head height behind a flow restriction (flume or weir)
Sensors can be floats, ultrasonic level sensors, ultrasonic uplooking sensors, etc.

[daqmaster]

How to select a flow meter

Ask the following questions:

How much do I want to spend?

How accurate do I want the flow device to be?

How "good" is the installation -- how "good" should it be?

How long do I want the flow device to last? (think durability vs. relaibility)

More on flow meters...