Static pressure vs total pressure vs dynamic pressure
Pressure transmitters usually measure two pressure values: static pressure and dynamic pressure. However, there are actually three. This article delves into the three types of pressure in detail.
Types of pressure
Static pressure is the force exerted on a fluid at rest. Imagine a bucket of water sitting on the ground with a rubber duck in it. As long as everything stays still, static pressure exists in that bucket. If you attached your transmitter, it would only give you the value for static pressure. You can consider it the default, as most transmitters measure static pressure.
Dynamic pressure comes next, right? Not quite. Before we get to dynamic pressure, let’s talk about total pressure. Total pressure is the force measured when moving fluids stop. If you pick up the bucket, the water will slosh around in it. The force exerted on the bucket by the sloshing water, which is stronger and less static than static pressure, is total pressure.
Now, remember the duck floating on the water? If you attached the transmitter to it instead of the bucket, he would still measure static pressure, because it moves with the water.
Dynamic pressure is the difference between total and static pressure. Dynamic pressure measures the kinetic energy of a fluid, which comes from the fluid’s velocity and density. So dynamic pressure happens in the movement between the point where the water starts moving and the point where it stops.
Usually, you’ll find both sensors in multivariable pressure transmitters. The transmitter has static and differential sensors built-in and working separately, sending their data to the control system.