Absolute pressure sensors and gauges produce readings that are not influenced by atmospheric pressure. Instruments such as altimeters and barometers display vacuum-referenced absolute pressure measurements. This article explains what absolute pressure is and the importance of measuring it.

The Earth’s atmosphere has weight and creates pressure. The amount of this atmospheric pressure – also called ambient pressure – varies by altitude. The higher the location, the less atmosphere is available to press down on a surface. Atmospheric pressure also varies depending on weather conditions.

Gauge pressure (atmospheric pressure + the measured pressure) is adequate for most pressure measurement needs, but atmospheric pressure varying by altitude and weather can affect accuracy in specific applications.

Instrument manufacturers developed absolute pressure gauges and absolute pressure sensors for applications that require readings not influenced by changes in altitude or weather, such as in meteorological and aviation applications. An absolute pressure sensor is a sealed system that functions by referencing a perfect vacuum, so it produces pressure readings that do not include the effect of atmospheric pressure.

Understanding Absolute Pressure

Most electronic pressure sensors measure gauge pressure based on the deformation of a diaphragm. If the diaphragm is exposed to the process pressure on one side and vented on the other side (exposed to ambient pressure), the deformation is reduced by the amount of ambient pressure. This means a gauge pressure reading is actually the pressure difference between the process pressure and the atmospheric pressure.

With absolute pressure sensors, the side of the sensor not in contact with the pressure media is exposed to an absolute vacuum chamber that is permanently sealed. The deformation of the diaphragm is not impacted by atmospheric pressure because it uses the sealed vacuum as its reference and zero point.

Applications for Absolute Pressure Sensors

Absolute pressure sensors and absolute pressure gauges are typically found in applications that require the monitoring of industrial high-performance vacuum pumps. For example, industrial packaging machines, for example, are used for vacuum packaging of medical products in a clean environment to ensure sanitary and bacteria-free delivery to hospitals and doctors.

In the food industry, vacuum packaging is utilized when the highest level of vacuum possible is required to prevent oxygen from degrading perishable food, thereby greatly extending the product’s flavor and shelf life.

Conventional pressure gauges and sensors, which are affected by influences in the atmosphere, are unable to monitor the high end of a vacuum.

Applications requiring true absolute pressure sensors and gauges can also be found in scientific laboratories, universities, the military, and the aviation industry.

WIKA offers high-precision absolute pressure sensors and transmitters for a number of applications, including the Model P-30 (standard version) and Model P-31 (flush version) pressure transmitters, ideal for use in labs, machine building, and calibration.

This WIKA reference page offers more details on gauge pressure and absolute pressure, and also explains the basic concepts behind differential pressure measurement.

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