DP Level Transmitter Range Calculator
The Fundamental Equation
A Differential Pressure (DP) transmitter measures the difference between the High Pressure (HP) side and the Low Pressure (LP) side.
1. Open Tank Application
The LP side is vented to atmosphere (0 psig). The HP side senses the fluid weight.
- LRV (0% Level): Usually 0 mmH2O (unless elevated).
- URV (100% Level): SGprocess × Height.
2. Closed Tank (Wet Leg / Capillary)
When a tank is pressurized, we must compensate for the vapor space pressure. If condensation occurs in the LP leg, we fill it intentionally (Wet Leg) or use remote seals with capillaries.
This introduces Zero Elevation or Zero Suppression.
PHP = Pgas + (SGproc × Hlevel) + (SGfill × hHP_leg)
PLP = Pgas + (SGfill × hLP_leg)
ΔP = (SGproc × Hlevel) + (SGfill × hHP_leg) - (SGfill × hLP_leg)
Field Note
Always remember: Span = URV - LRV. The span remains constant regardless of elevation or suppression. The transmitter simply shifts its 4-20mA output window relative to absolute zero differential.
Thanks for the tool