In closed tanks, the DP transmitter must compensate for the pressure of the vessel above the liquid surface. So the LP side of transmitter is connected to the tank. Here in this post we are discussing about calibration of DP transmitter for a closed tank with wet leg & constant level application for density measurement. This is only used for constant level application.
|Density Measurement using DP Transmitter for closed tank with wet leg|
The minimum and maximum process specific gravities can be obtained from process datasheets.
The formulas for calculating the tranmitter LRV and URV are;
HP Side/LRV/4ma = L.Smin – H.Sref
LP Side/URV/20ma = L.Smax – H.Sref
L = Closed tank maximum measured level
H = Height of wet leg
Smax = Maximum process specific gravity
Smin = Minimum process specific gravity
Sref = wet leg or reference leg specific gravity
Note: This calculation is only used for closed tank with wet leg and for constant level application.