There are several different ways to measure pressure in a system, or more accurately the change between two different pressures or points within a system. The formula for gage pressure measurement is relatively simple, and it is the absolute pressure minus the atmospheric pressure. This is one of the most common pressure measurements used today.
The atmospheric pressure actually measures the weight of the air based at a specific altitude above sea level. The atmospheric pressure will increase when measurements are taken closer to or below sea level, and decrease as the altitude increases. Atmospheric pressure can also change based on the temperature and other conditions of the air. For this reason, the atmospheric pressure is not an absolute measurement.
Absolute pressure, on the other hand, is a constant. It is developed or referenced against the pressure in a perfect vacuum. This is why it is essential to consider the atmospheric pressure in the calculations using gage pressure measurement.
The Advantage of Using Gage Pressure
All of the different designs of gauge pressure sensors are constructed with a specific vent in the sensor. This vent allows the sensor to access the specific atmospheric pressure where the gauge is used, not against an arbitrary factor such as absolute pressure.
The advantage here is that the gage pressure measurement will always be accurate, based on the location where the strain gauge is used. The differences in the atmospheric pressure are accounted for in the measurement, which provides accurate operation of the system, regardless of the altitude or location of the device.
This is critical to avoid overloading systems when used in different altitudes and under different atmospheric conditions. Without this, the readings from the gauge pressure sensor would not be accurate, based on the conditions the system was operating under.
The Uses of Gage Pressure Sensors
Most of the pressure readings people use in everyday life are going to be gage pressure. This includes hand-held tire pressure gauges as well as the automated tire pressure sensors in new models of vehicles.
Other systems that use gauge pressure measurements include blood pressure measurement, hydrostatic liquid measurements, liquid or gas movement through systems. Choosing the different styles of pressure sensors will allow the designer to factor in the speed of the sensor, the temperature the sensor will be used in and the actual capacity of the sensor to monitor the degree of change to the accuracy required.