1.8.2 Turn-down ratio
The turn-down ratio is the ratio of the maximum flow rate to the minimum flow rate for a
measuring range that is within a stated accuracy. For example, the measuring range of a
magnetic flow meter might be 0.3 m/s to 12 m/s within an accuracy of 0.3%. This would thus
be stated as having a 40:1 turndown ratio (0.3 %). In addition the measuring range might
extend from 0.2 m/s to 12 m/s within an accuracy of 0.5%. In this case the turndown ratio is
60:1 (0.5%). It is, therefore, meaningless to express the turndown ration without a specified
accuracy.