For many negative pressure or vacuum pressure applications, 2 types of pressure sensors are available: gauge sensors or absolute pressure sensors. The reference pressure is the differentiating factor between these 2 types of sensors. The diagram below illustrates how the different methodologies work.
Absolute pressure sensors reference a vacuum, or zero pressure, and their full-scale pressure range is atmospheric pressure, which is about 14.7 psi at sea level (see item A). Hence, users have the capability of measuring up to negative 14.7 psi range of pressure.
In the case of a gauge sensor, either a single port or dual port model can be used. In the case of a dual port gauge sensor, the "lower pressure" port measures the negative or vacuum pressure (B). By accessing the "lower pressure" port, the user is mimicking applying a positive pressure to the higher pressure port as in pressure range (C). The advantage of using a gauge sensor is if the user wants to measure a vacuum smaller than the full vacuum range 14.7 psi, such as -3 psi, using a lower range focusing on the negative pressure range is more appropriate. This way, by using a smaller full-scale range pressure sensor, the user captures the the full-range of the vacuum pressure measurements, thus obtaining more resolution and more design flexibility. For a single port gauge sensor, the single port is vented to atmosphere.
For example, if a user is trying to measure the inhalation pressure in a respiratory application, the pressure range would be no more than 0.6 psi. If an absolute pressure sensor is used, only 4% of the pressure range would be used, hence wasting 96% of the sensor's calibrated range. By using a gauge sensor such as the SM7XXX Series, the user can capitalize on higher resolution and measure smaller negative pressure ranges.
Examples of classic applications where negative pressure measurements are needed include negative wound pressure therapy, breathing applications, pump control/performance monitoring, HVAC applications such as filter monitoring and pressurized rooms such as cleanrooms and isolation rooms.
We also have a Low Pressure Product & Pricing Guide which reviews specific models and includes budgetary pricing.