A DP transmitter must be calibrated to measure the level of a liquid in an open tank. The density of the liquid is 1000 kg/m3. The DP transmitter will be mounted one meter below the bottom of the tank.
The tank is full when the height of the liquid in the tank is 5 meter and it is empty when there is only liquid in the high pressure line connected to the DP transmitter.
Determine the necessary calibration specifications for an output signal of 4 to 20 mA.
DP Transmitter Calibration for Liquid Level Tank
Empty:
P1 = Patm + ρhg
= Patm + 1000×1×9.81
= Patm + 9810
∴P1 – P2 = 9810 Pa
Full:
P1 = Patm + ρhg
= Patm + 1000×6×9.81
= Patm + 58860
∴P1 – P2 = 58860 Pa
Calibration specification:
Output = 4 mA when input = 9810 Pa (empty condition)
Output = 20 mA when input = 58860 Pa (full condition)