Pressure Measurements with DAQ Systems
Overview
This application note describes pressure sensors and explains how they work. It also details the requirements for
measuring pressure and the signal conditioning required for the measurement. It explains how to use NI data acquisition
(DAQ) systems to measure bridge-based sensors, and recommends three different starter kits for pressure
measurements. Finally, an appendix is included explaining other less common pressure sensors and their areas of
application.
For in-depth guidance on making a pressure measurement, visit the how-to guide.
What Is Pressure?
Pressure is defined as force per unit area that a fluid exerts on its surroundings.[1] There are two pressure measurement
types: absolute and gauge. Absolute pressure is referenced to the pressure in a vacuum, whereas gauge pressure is
referenced to another known pressure level, usually the ambient atmospheric pressure. The SI unit for pressure is the
Pascal (N/m2), but other common units of pressure include atmospheres, bars, inches of mercury, millimeters of
mercury, and Torr.
Pressure Sensors
Because of the great variety of conditions, ranges, and materials for which pressure must be measured, there are many
different types of pressure sensor designs. Often we measure pressure by converting it to some intermediate form, such
as displacement, which we can then measure with a sensor. Different methods are available for measuring pressure
depending on whether the pressure being measured is greater or less than atmospheric pressure. Of all the pressure
sensors, Wheatstone bridge (strain based) sensors are the most common, offering solutions that meet varying accuracy,
size, ruggedness, and cost constraints. For information on other types of sensors, refer to the Appendix at the end of this
document.
Bridge sensors are used for high- and low-pressure applications, and can measure absolute, gauge, or differential
pressure (the difference in pressure between two different points of interest). All bridge sensors make use of a strain
gauge and a diaphragm (see Figure 1).
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