DP Level Transmitter Calculation for Diaphragm seal type with capillary tube

For determining the DP level transmitter calibration range for this type, we need fill fluid density inside the capillary tube, Process fluid density, Distance between HP & LP tapping points, Maximum level to be measured.

Sometimes distance between HP & LP tapping points and Maximum level to be measured are same or may be different and entirely depends on your application, transmitter installations or process requirement.

If the transmitter capillary tube is filled with same fill fluid then no need to consider transmitter mounting elevation. The transmitter mounting elevation must be considered when one diaphragm is connected and other diaphragm opened to atmosphere. Here in this example we considered same fill fluid in capillary tube and both diaphragms are connected to the tank.

DP Level Transmitter Calibration for Diaphragm Seal with capillary tube type

The formulas for calculating transmitter URV and LRV are as follows:

HP Side or LRV or Transmitter 0% = – ρF . g .H2

LP Side or URV or Transmitter 100% = (ρP . g . H1) – (ρF . g . H2)

Where

H1 = Maximum level to be measured
H2 = Height difference between HP & LP tapping points
ρP = Process fluid density in the tank
ρF = Fill fluid density inside the capillary tube
g = Gravitational acceleration

Note:

1.In this example the tank maximum level (100%) to be measured (H1) is considered below the LP tapping point height (H2).

2.In some cases maximum level to be measured and LP tapping point height may be same. Hence enter Height difference between HP & LP tapping points value in H1 & H2

The Following tables specifies the fill fluid constant values: