What’s the difference between absolute, gauge and differential pressure sensors? Different applications require different ways of measuring things. In electronic systems, as an example, sometimes we want to know the voltage across a specific component. Other times we’re only interested in the difference in voltage between two points in the circuit.
It’s a similar situation when we’re measuring the pressure of liquids and gases. And for each situation there’s a pressure sensing method that best matches the application. An absolute pressure sensor provides a pressure measurement relative to a reference of zero pressure. This reference pressure is as close as possible to a vacuum (as shown in the diagram above).
This can be compared to measuring temperature in Kelvin, a measurement unit that uses the coldest possible temperature, 0 °K, as its reference point. A pressure measurement of 1 bar will be the same, regardless of where in the world, or at what altitude, it’s measured. Gauge pressure sensors provide a pressure measurement relative to the local atmospheric pressure. This is comparable to measuring a DC voltage with a voltmeter, where the voltage at the red probe is either positive or negative with respect to the point to which the black probe is connected.
If the gauge pressure sensor measures a pressure of 1 bar in a vessel, this is 1 bar more than the atmospheric pressure. A1 bar reading at high altitude (where air pressure is lower) would mean the pressure in the vessel has a lower absolute pressure than A1 bar reading at sea-level.
Finally, differential pressure sensors measure the difference in pressure between two points in a system. Typically, this is because this difference can be used to measure the flow of a liquid or a gas in pipes or ducts. Alternatively, it may simply be used to detect a blockage or seized valve. If the pressure before a valve is higher than after it (in the direction of flow), there must be something impeding the progress of the media between the two measurement points.