Chapter 9 - Encoders, Transducers, and Advanced Sensors
300psi Figure 9-13 - Discrete Output Pressure Switch Symbols
Strain gage pressure sensor The strain gage pressure sensor is the most popular method of making analog measurements of pressure. It is relatively simple, reliable, and accurate. It operates on the principle that whenever fluid pressure is applied to any solid material, the material deforms (strains). If we know the strain characteristics of the material and we measure the strain, we can calculate the applied pressure. For this type of measurement, a different type of strain gage is used, as shown in Figure 9-14. This strain gage measures radial strain instead of longitudinal strain. Notice that there are two different patterns of strain conductors on this strain gage. The pair around the edge of the gage (we will call the “outer gages”) appear as regular strain gages but in a curved pattern. Then there are two spiral gage patterns in the center of the gage (we will call the “inner gages”). As we will see, each pattern serves a specific purpose in contributing to the pressure measurement.
Figure 9-14 - Diaphragm Strain Gage (Omega Instruments) 9-15