Control Valve · Glossary

What is Split Range Control?

two valves from one outputControl Valve

Split range control uses one controller output to operate two valves, each over part of the signal range.

Split Range Control Explained

A typical split gives valve A the 0 to 50 % output and valve B 50 to 100 %. It is used for heating and cooling, or for a small and a large valve to widen rangeability.

Overlap or gaps at the split point cause bumps in control, so the ranges are set and tested carefully in the positioners or in the control system.

Split Range Control Formula

Valve opening = (Signal − Start) ÷ (End − Start) × 100 %

Start, End

signal range assigned to that valve

Example: Valve B on 12 to 20 mA at 16 mA: (16 − 12) ÷ 8 = 50 % open.

Calculators for Split Range Control

CalculatorSplit Range CalculatorFree online calculator with formula and worked example.CalculatorValve Rangeability CalculatorFree online calculator with formula and worked example.

Frequently Asked Questions

What is Split Range Control?

Split range control uses one controller output to operate two valves, each over part of the signal range.

Split in positioners or in the DCS?

Splitting in the DCS with two outputs is more flexible and easier to diagnose; positioner splitting saves an output.

Why does the loop gain change at the split?

The two valves have different capacities, so the process gain jumps.

Learn more on the blog

Control valve positioner working

A practical guide on instrumentationblog.in with more detail on split range control and how it is applied on real plants.

Read Full Article

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