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Engineering ToolBox > Flowmeters and Accuracy

An introduction to accuracy in flow measurement devices

Accuracy indicates how close the measured value is to the accepted or true value.

The accuracy of flowmeters can be stated as:

• percent of full span
• percent of rate

Accuracy as Percent of Full Spann

Accuracy in percent of full span can be expressed as:

a_% = a 100% / s (1)

where

a_% = relative accuracy (%)

a = +/- absolute accuracy

s = full scale of the flowmeter

Example - Accuracy of Flowmeter in Percent of Full Span

If the absolute accuracy is +/- 10 kg/h - the relative accuracy at full scale 1000 kg/h can be calculated as:

a_% = (+/- 10 kg/h) 100% / (1000 kg/h)

    = +/- 1%

The relative accuracy at full scale 100 kg/h can be calculated as:

a_% = (+/- 10 kg/h) 100% / (100 kg/h)

    = +/- 10%

Accuracy as percent of Rate

Accuracy in percent of rate can be expressed as:

a_% = a 100% / q (2)

where

a_% = relative accuracy (%)

a = +/- absolute accuracy

q = flow rate

Example - Accuracy of Flowmeter in Percent of Rate

If the relative accuracy is +/- 1% of rate - the absolute accuracy at rate 1000 kg/h can be calculated as:

a = (+/- 1%) (1000 kg/h)

    = +/- 10 kg/h

The absolute accuracy at rate 100 kg/h can be calculated as:

a = (+/- 1%) (100 kg/h)

    = +/- 1 kg/h