# Easy way to calculate Range for Differential Pressure Level Transmitter?

Differential Pressure (DP) level measurement is a widely used method in various industrial applications to measure fluid levels in tanks, silos, and other containers. This method works by measuring the pressure difference between two points, which is proportional to the height of the fluid in the container.

The DP level measurement system consists of a differential pressure transmitter, a diaphragm seal, and a capillary tube. The diaphragm seal is attached to the top of the container, and the capillary tube is filled with a fluid that has a known density. The DP transmitter measures the pressure difference between the two ports and converts it into a level measurement.

The accuracy of the DP level measurement system depends on several factors, including the density of the filling fluid, the length of the capillary tube, and the temperature of the fluid. To ensure accurate measurements, it is important to take these factors into account when calculating the calibrated range of the DP level transmitter.

### Sample Process Data

Process fluid density (SG1) = 0.96 g/cm3
Fill fluid density (SG2) = 0.96 g/cm3
Wet Leg Heigh (H) = 1.0 m = 1000mm
Distance between transmitter & HP tapping point(h) = 0.2 m = 200mm
Tank Height (L) = 0.7 m  = 700mm

#### When level at 0% = 4mA

∆P at 0% level
∆P = HP – LP
HP = SG1 x h = 0.96 x 200 = 192 mmH2O
LP = SG2 x (H) = 0.96 x 1000 = 960 mmH2O

Therefore Range at 0% is
HP – LP = 192 – 960 = -768 mmH2O

## When level at 100% = 20mA

∆P at 100% level
∆P = HP – LP
HP = SG1 x (L + h) = 0.96 x 900 = 864 mmH2O
LP = SG2 x (H) = 0.96 x 1,000 = 960 mmH2O

Therefore ∆P at 100% is
HP – LP = 864 – 960 = -96 mmH2O

Scaling to set to Differential Pressure Transmitter
0% to 100% = -768 ~ -96 mmH2O

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