Question

What is the term for the ratio of the actual flow rate to the maximum rated flow rate of a flow meter?

• A. Repeatability
• B. Linearity
• C. Turndown ratio
• D. Accuracy

Hint:

Turndown ratio tells you how flexible a flow meter is — the higher the ratio, the wider the range of flow rates it can handle.

Answer 1

The Correct Option is C

The turndown ratio of a flow meter is defined as the ratio of the maximum flow rate to the minimum flow rate at which the meter can measure accurately.
However, when phrased inversely — the ratio of actual (or minimum) flow rate to the maximum flow rate — it still refers to the same characteristic, just expressed in reverse order.
Mathematically:
\[ \text{Turndown Ratio} = \frac{\text{Maximum rated flow rate}}{\text{Minimum measurable flow rate}} \]
It is a key parameter for selecting flow meters because it tells us how flexible the meter is in handling a wide range of flow conditions.
Let’s review the other options:
- (1) Repeatability refers to how consistently a flow meter can reproduce readings under the same conditions.
- (2) Linearity measures how closely the meter’s output follows a straight line over its range.
- (4) Accuracy is the closeness of a measured value to the true value — it doesn't describe a range.
Only option (3) describes the concept of the ratio between flow rates — the turndown ratio.