Flow Meter Turndown Ratio Calculator
Check the turndown ratio your application needs and what it means for linear meters and square law DP meters.
- Turndown = max ÷ min = 100 ÷ 20 = 5 : 1
- DP meters: ΔP ∝ Q², so DP turndown = 5² = 25 : 1
Turndown Formulas
DP meters: ΔPmax ÷ ΔPmin = (Qmax ÷ Qmin)²
Worked example
A process needs 20 to 100 m³/h, a 5 : 1 turndown. An orifice would need a 25 : 1 DP range, with minimum flow at only 4 % of maximum DP.
Frequently Asked Questions
What is turndown ratio?
The ratio of maximum to minimum flow a meter can measure within its stated accuracy.
Why do DP flow meters have low turndown?
Because DP falls with the square of flow, low flows give a tiny DP that is hard to measure accurately.
Is turndown the same as rangeability?
They are often used interchangeably, although rangeability sometimes refers to the inherent capability of the meter type.
Learn more on the blog
What factors affect the stability of flow meter readings?
A practical, field focused guide on instrumentationblog.in that explains the theory behind this calculator and how engineers apply it on real plants.
Read Full Article