Flow measurement basics

Hello Economist,

Some points to consider:

• The nature of sensors used in flowmeters (or any sensor for that matter) limits the accuracy to a range.
• Sensors do not give linear outputs in the lower ranges and near zero.

Let's take an example:

A Typical Mass Flowmeter:

• Maximum Measureable Flowrate: 100 lb/minute
• Minimum Measureable Flowrate: 10 lb/minute
• Accuracy of Full-scale: 0.4%
• Accuracy of Reading: 0.8%
• Turndown Ratio: 10:1 (or just 10)

• The Range is the Maximum Measureable Flowrate minus the Minimum Measureable Flowrate. In this case it is 90 lb/minute.
• The Turndown Ratio is the Maximum Measureable Flowrate divided by the Minimum Measureable Flowrate.
• The "Accuracy of Reading" specification means that, measured values between the Maximum and Minimum Measureable Flowrates, compared with the actual flowrate value, your accuracy will always be 0.8% or lower.
• The "Accuracy of Full-scale" specification means that, compared with the Maximum Measureable Flowrate of the meter, the actual flowrate accuracy will be 0.4% or lower.

Metrology is a vast and fascinating field. If you want to learn more, I suggest that you look up and study these:

• Turndown Ratio
• Accuracy
• Repeatability
• Precision
• Standards
• NIST

With all of the information available over the internet, you can learn much.

Mike