Next to temperature, pressure is one of the most important physical state variables. The pressure is defined as a force (FN) which acts uniformly over a defined area (A). The different types of pressure are differentiated only by the reference pressure.
Whether absolute pressure, gauge pressure or differential pressure. With WIKA, you will find the right measuring instrument for each type of pressure:
Accordingly, in order to measure differential pressure, at first two different pressures are captured in a measuring instrument. Only if the measured values differ from each other, will a differential pressure be indicated. Instances where it is required to measure differential pressure are, for example, level measurement and monitoring applications.
A positive overpressure is referred to when the absolute pressure is greater than the atmospheric pressure. In the opposite case, one speaks of negative overpressure. In order to avoid misunderstandings, the term vacuum, previously used for this overpressure with a negative sign, is no longer used as a description of a variable. However, the term is still used to describe a state, e.g. “vacuum chamber” or “a vacuum exists in the intake manifold”. In the same way, where there are word compositions with overpressure, the “over” part is omitted if the associated variable is clearly defined as an overpressure, e.g. blood pressure or tyre pressure.
The indices of the formula symbols “abs”, “amb” and “e” clearly define the reference point of the respective pressure. They are only attached to the formula letter p, and not to the unit symbols.