## Expert’s answer: What’s the difference between static and dynamic pressure?

Your transmitter measures two pressure values (static and dynamic pressure), but you actually have three.

Static pressure describes 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 it.

Dynamic pressure comes next, right? Not quite. Before we get to dynamic pressure, let’s talk about total pressure. Total pressure occurs when moving fluids stop. If you pick up the bucket, the water will slosh. The force exerted on the bucket by the sloshing water qualifies as total pressure.

Now, remember the duck? If you attached the transmitter to him instead of the bucket, he would still measure static pressure, because he moves with the water.

However, he would also measure dynamic pressure, the difference between total and static pressure. Dynamic pressure means 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 started and the point where it stops.

Usually, you’ll find both sensors in multivariable devices like yours. The transmitter has static and differential sensors built in and working separately, sending their data to the control system.

These vendors have multivariable transmitters:

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