There are a variety of strategies for measuring the pressure in a gauge sensor. Most of them use a membrane that is fitted with an electrical component, such as a resistor, whose value varies when flexed.
Nowadays, microelectromechanical systems, commonly known as MEMS, are utilized. Small and light structures are etched into silicon that can flex or vibrate. Since the base medium is silicon, further electronic circuitry can be integrated alongside the MEMS element. The short electrical paths help to ensure low noise and high measurement accuracy, whilst the MEMS element can result in a pressure sensor that is better isolated from temperature changes.
In some applications the exact pressure or vacuum being generated is not of key importance. Instead, you just want to understand how much the pressure or vacuum differs in comparison to atmospheric pressure. Atmospheric pressure varies across the globe depending on our altitude and even changes in the weather.
Consider, as an example, the vacuum pumps used during or after surgery. These are used to remove bodily fluids, gases and even tissue. Typically, only a small, finely controlled vacuum is required in order to avoid injury. This needs to be set in relation to the local atmospheric pressure. In a hospital at sea level, the atmospheric pressure will be higher than at a hospital high in the mountains.
A gauge pressure sensor measures the pressure at its port with respect to the local atmospheric pressure. This can be compared to using a multimeter’s DC measurement range, where the display shows the voltage at the positive probe with respect to the negative probe. Gauge pressure sensors are typically packaged with a port, to which a pipe can be attached, as well as a vent that is open to the atmosphere. The pipe can then be connected to the system where the measurement is to be made.