Ray-Level DP Transmitter Level Calculator

Inputs

Mode
Elevationsfrom Zero Datum (tank bottom)
Fluid density
elev up0Zero Datum200 mm0%LRV 1.77 kPa700 mm100%URV 6.18 kPaSpan500 mmLN 0 mmUN 700 mmHPdryLPDPTx 0 mm900 kg/m³ · dry legspan 500 mm50 %DP 3.97 kPa

Results

LRV1.77kPa
URV6.18kPa
Range4.41kPa

Vapour head appliedincl. vapour-column weight

LRV1.79kPa
URV6.18kPa
Range4.39kPa

Live reading

Live DP @ 50.0%3.97kPa
0%100%
About DP transmitter level measurement

Every height is an elevation in millimetres measured up from the Zero Datum — the bottom of the tank. The transmitter reads the hydrostatic head of liquid above it; expressing pressure in mmwc lets a density of rho kg/m3 act as a column factor of rho/1000 (1 mmwc = 1 mm of water).

Dry-leg configuration

The LP (low-pressure) reference leg is open/gas-filled — no liquid fills it. The transmitter measures the process head above its own elevation.

LRV = (E0% - E_tx) * rho/1000
URV = (E100% - E_tx) * rho/1000

Wet-leg configuration

The LP leg is filled with a seal fluid from the upper nozzle down to the transmitter. Its back-pressure subtracts from the reading, often producing a negative LRV.

LRV = (E0% - E_tx) * rho_p/1000
      - (E_up - E_tx) * rho_s/1000

Capillary seals

Both impulse paths are remote seals connected by capillary tubes filled with the same fill fluid. The transmitter elevation cancels; only the seal separation drives the back-pressure.

LRV = (E0% - E_lo) * rho_p/1000
      - (E_up - E_lo) * rho_f/1000
URV = (E100% - E_lo) * rho_p/1000
      - (E_up - E_lo) * rho_f/1000

Vapour head applied

The base formulas assume the vapour space cancels on both legs. The vapour above the liquid has weight, though: a column reaching from the liquid surface up to the upper nozzle adds (E_upper - E_level) * rho_vapour/1000 to the head — largest at 0% and vanishing once the liquid reaches the upper nozzle. Set a vapour density to see this second LRV/URV pair (dry/wet modes only).

The formulas give a head in mm of water column; results are shown in kilopascals (1 mmwc ~= 0.00981 kPa).

Zero DatumBottom of the tank — elevation 0; every height is measured from here
TransmitterElevation of the DP transmitter (not used in capillary mode — it cancels)
0% / 100%Elevations of the 0% and 100% level marks (their gap is the span)
Lower nozzleLower impulse tap / lower remote seal (E_lo in capillary mode)
Upper nozzleUpper impulse tap / upper remote seal (E_up)
DensityLiquid rho_p; seal rho_s (wet) or fill fluid rho_f (capillary) in kg/m3
Vapour densityVapour-space density in kg/m3 — drives the vapour-head-applied LRV/URV (dry/wet only)

Formula references: Dry & Wet Leg · Capillary Remote Seal