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Differential Pressure · Interactive Instrumentation Guide
Differential Pressure Across a Filter
Adjust upstream and downstream pressure independently, or reverse the connections to see the sign change.
Custom process schematic · not to scale · blue H connection / orange L connection, where applicable.
Application settings
Equation and live calculation
ΔP = P_H − P_L; I_ideal = 4 + 16(ΔP − LRV)/(URV − LRV)
Live substitution appears when the demonstration loads.
PV = process value; LRV/URV = lower/upper range values; I = current in mA. Pressure calculations use kPa internally. Selected units apply to inputs, limits, diagrams, and readouts; changing units converts the same physical values without changing the current. Tank calculations use meters internally; z is positive above the bottom tap. ρ = 1000 × specific gravity in kg/m³; g = 9.80665 m/s². H in tank equations means measured height, not the H port. Entered LRV/URV define the current scaling; calculated empty/full tank DP values are reference checks. Set and Reset Points define switch operation; deadband is their absolute difference. Temperature reference equations use °C internally. Mercury pressure units use conventional NIST conversion factors. Vacuum entries are negative gauge pressure; the absolute-pressure readout remains nonnegative. Models assume ideal instantaneous response. Displayed current is limited to the nominal 4–20 mA range: I_display = clamp(I_ideal, 4, 20), where clamp holds a value at its lower or upper limit. This teaching limit does not reproduce manufacturer-specific saturation or alarm currents.
Where it is used
Filter restriction monitoring, heat-exchanger pressure loss, and differential pressure measurement.
What the demonstration shows
The transmitter subtracts its L port pressure from its H port pressure. Common pressure cancels while pressure difference remains.
Common mistake to avoid
H and L identify ports. Reversing the lines reverses DP; the H port is not guaranteed to have the greater pressure.
Model assumptions
Ideal proportional transfer with no damping or measurement error. The teaching model limits current to 4–20 mA; manufacturer-specific saturation and fault-current logic are excluded. Display-unit changes preserve the same physical values.
Technical references
Emerson — Differential pressure level measurementNIST — SI unit conversion factors (conventional mercury units)Educational model. Consult the instrument manual for installation, configuration, limits, and approved test procedures. No connection to live plant equipment is made.