Absolute, gauge, and differential pressure

Pressure Q&A

I need to measure the pressure in a water pipe. Should I use a differential pressure transmitter or a gauge or absolute pressure transmitter?

Expert’s answer: Absolute, gauge, and differential pressure

Let’s start with the differences between absolute, gauge, and differential pressure. Then you can check each option to see which will suit your needs.

To measure anything, you always need a reference point. These pressure types differ mainly in their reference points.

Gauge pressure uses the ambient air around the sensor for reference. The sensor usually has a vent to access the atmosphere. It compares that pressure to the pressure of the product to provide data. That means that gauge pressure always reflects local conditions, which can factor into your use.

Absolute pressure uses a perfect vacuum for its reference, starting from zero, if you will. This means it measures atmospheric pressure and product pressure together. Because it uses a stable reference point, it can give more definite data than gauge pressure.

Differential pressure compares the pressure of two different areas. You could even call gauge pressure differential, because it compares ambient pressure to product pressure. However, typically differential compares the pressure of a product in two different areas. For instance, if you set up a sensor on an orifice plate, then it would measure the pressure on both sides of the plate to display the difference.

Absolute, gauge, and differential pressure
Pressure transmitter – courtesy of ABB

In your case, if you have water flowing through a pipe in a closed system, then you’ll probably use a gauge sensor. It’ll measure the pressure of the system against your current atmospheric pressure.

However, if you have a vacuum in your system, then you should use an absolute sensor. You can use a gauge sensor if you prefer, but an absolute sensor will give you a more precise measurement, should you need it.

I’ll take a guess and say you don’t have a vacuum, so I recommend the gauge sensor. Whatever you decide to use, you have plenty of options on the market to support that choice.

All these companies offer various pressure transmitters:

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