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Pressure · Interactive Instrumentation Guide
Vacuum Pressure Transmitter
Change process pressure and see the reference, engineering value, and ideal 4–20 mA signal.
Custom process schematic · not to scale · blue H connection / orange L connection, where applicable.
Enter vacuum as negative gauge pressure. Changing pressure units converts existing values; it does not change the pressure reference.
Application settings
Equation and live calculation
P_abs = P_gauge + P_atm; I_ideal = 4 + 16(PV − 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
Sub-atmospheric processes expressed as negative gauge pressure.
What the demonstration shows
Gauge pressure is relative to atmosphere. Absolute pressure uses a vacuum reference: P_abs = P_gauge + P_atm. Current follows the configured range.
Common mistake to avoid
Do not mix gauge and absolute ranges. A vacuum is a negative gauge pressure, not a negative absolute 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
WIKA — Pressure measurement referenceNIST — 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.