Square-Root Extraction
Flow through a restriction follows the square root of differential pressure. A DP cell reads linearly in pressure, so flow needs the square root taken. Enter a signal and read the flow, or enter a flow and read the signal, both directions, with the differential-pressure and flow ranges side by side.
Ranges
Calculate
% Differential pressure
—%
% Flow
—%
Differential pressure
—inH2O
Flow
—GPM
DP-linear signal
—mA
Flow-extracted signal
—mA
Two signals, one flow. A plain DP transmitter outputs DP-linear mA: 12 mA is 50% of differential pressure but about 70.7% of flow. A transmitter with extraction on (or the DCS doing it) outputs flow-extracted mA: 12 mA is 50% of flow. The tool shows both so you can tell which one you are looking at.