contact us


On Flow Measurement F-0005

Description of Accuracy of Flowmeters

Accuracy is the key factor of flowmeters. Two different ways of indication of the flowmeter accuracy are often used as follows;

[1] ± OO% of Full Scale ( OO% F.S.)

This is to indicate the accuracy of flowmeter against full scale range.
For example, when the subject flowmeter has 100m3/h full scale range with 1.5% F.S. accuracy, the absolute error which might be involved is ;

100m3/h × 0.015 = 1.5m3/h

This estimated error is applicable through the whole scale range. Even when the actual flow rate is 50m3/h (50% of Full Scale), still the possible error is 1.5 m3/h.
Thus, practical accuracy at 50% of full scale is;

1.5m3/h × 50m3/h = ± 3.0 %

The actual / practical accuracy curve of the Full Scale Accuracy is expressed by the following Graph;
(Typical accuracy graph of Rotameters)

Accuracy against the flowTypical accuracy graph of Rotameters

Flow rate

[2] ± OO% of Reading (Indicated value) ( OO% R.D.)

This means that the accuracy is against the measurement value. ± 1.0% R.D. means 1.0% accuracy is guaranteed for through the scale range. However, flowmeters may often have minimum possible measuring point with accuracy limit. Lower than this point, the accuracy will not be guaranteed or different/separate description of accuracy is applicable.
The following is the typical indication curve of "± 0.5% R.D" from our Magnetic Inductive Flowmeters;

Accuracy against the flow Accuracy against the flowFlow rate