Pressure types are an important consideration in selecting pressure sensors or gauges for your application. They can seriously affect accuracy if misunderstood. This post will define the five different pressure types, and hopefully clarify which you need for your application.
This is the most common pressure type. It measures a positive pressure range, and its zero, or reference, point is set at ambient pressure. It is unaffected by barometric changes because it is open to the air, or vented.
Another very common pressure type. Like gage pressure, its zero point is ambient pressure, and it is vented – and therefore unaffected by barometric change. However, vacuum pressure measures a negative pressure range.
This pressure type measures both positive and negative pressure changes. Its zero is therefore set at ambient, and it is vented. In other words, compound gage pressure is really gage pressure and vacuum pressure combined.
This is when the pressure sensor is not vented. This is primarily done to protect the sensor; to avoid getting moisture or dust inside the sensor housing.
Because it is sealed, it is unavoidably affected by barometric change. It is not used in low-pressure applications because the barometric shift of a few psi would really affect accuracy. However, at 1,000 psi and above, the relatively small shift would go unnoticed.
Used when the zero point must be set to absolute zero. To achieve this, the sensor is also sealed, with all pressure sucked out of the housing. This is also unvented, and therefore affected by barometric change.
Unlike sealed pressure, absolute pressure is often used in low-pressure applications that want to measure atmospheric conditions. So, in this case, barometric change is okay.
Below is a quick reference chart for the different pressure types:
