Basic Equation for DP Level Transmitter Range Calculation

Liquid level height could be known by measuring its differential pressure using DP transmitter. Prior installation, DP transmitter shall be pre-set to calibrated range from calculation result. The formula to determine DP transmitter range is simply a Bernoulli principle equation. Having the transmitter set correctly, we can obtain the liquid level height by measuring the differential pressure between two differential points.

Bernoulli equation states:

Since the velocity within a tank is neglected, the equation becomes:

or

P1 + rho. g. h1 = P2 + rho.g.h2 = P3 + rho.g.h3

For any points within a tank, the above total elements shall be constant.

So, the deeper a point within a liquid, the more pressure exerted at that point. In other words, liquid pressure increases with elevation decreases and vice versa. For more clear understanding, see below picture showing their relationship.

Note that above formula shows that liquid density take into account on the calculation hence affects level measurement. The use of DP level transmitter is recommended only for application where liquid density does not vary considerably