Open and Closed Tank Level Calculations

Open Vessel Level Calculation

Open tank : Zero-Based Direct Mount Application

In above example, transmitter installed exactly at HP tapping point i.e. at 0 % Level

Calibration Range

LRV or 4mA point = 1.1 * 0 = 0 inH2O

URV or 20mA Point = Head = 1.1*50” = 55 inH2O

Cal. Range = 0 to 55 inH2O

Open Tank : Non-Zero-Based Direct Mount Application 

In above example, transmitter installed point and Tank Zero Percentage level are different.

Calibration Range

LRV or 4mA point = Head1 = 1.1*10” = 11 inH2O

URV or 20mA Point = Head2 = 1.1*50” = 55  inH2O

Cal. Range = 11 to 55 inH2O

Open Tank : Non-Zero-Based Remote Mount Application 

Calibration Range

LRV or 4mA point = Head1 = 1.1*10” = 11 inH2O

URV or 20mA Point = Head1 + Head2 = (1.1*10”) + (1.1*50”) = 66 inH2O

Cal. Range = 11 to 66 inH2O

Closed Tank Level Calculation (Wet Leg)

Closed Tank : Zero-Based Direct Mount Application 

In above example, transmitter installed exactly at HP tapping point i.e. at 0 % Level

Calibration Range

LRV or 4mA point =  Phigh – Plow = 0 – Head1 = 0 – (1.2*70”) = -84”H2O

URV or 20mA Point = Phigh – Plow = Head2 – Head1 = (1.1*50”)] – (1.2*70”) = -29”H2O

Cal. Range = -84 to -29 inH2O

Closed Tank : Non-Zero-Based Direct Mount Application 

In above example, transmitter installed point and Tank Zero Percentage level are different.

Calibration Range

LRV or 4mA point = Phigh – Plow = Head2 – Head1 = (1.1*10”) – (1.2*70”) = -73”H2O

URV or 20mA Point = Phigh – Plow = (Head2 + Head3) – Head1

= [(1.1*10”) + (1.1*40”)] – (1.2*70”) = -29”H2O

Cal. Range = -73 to -29 inH2O

Closed Tank : Non-Zero-Based Remote Mount Application

Calibration Range

LRV or 4mA point = Phigh – Plow = Head2 – Head1 = (1.1*10”) – (1.2*80”) = -85”H2O

URV or 20mA Point = Phigh – Plow = (Head2 + Head3) – Head1

= [(1.1*10”) + (1.1*50”)] – (1.2*80”) = -30”H2O

Cal. Range = -85 to -30 inH2O

Also Read: Basics of Hydrostatic Level