The Art of Practical and Precise Strain Based ... - Webprofile.info

Applications Note 1-13:FIGURE 1-49. Medium Isolation By ÒExclusionÓ:Silicone Gel FillSensorFlush Diaphragms:The second common type of strain-gaged diaphragm pressure sensor (Figure1-50) is the flush-diaphragm design where the sensing diaphragm isflush with the end of the sensor, eliminating all dead-volume cavities. Theadvantage of this style of sensor is that the elimination of the Helmholtzcavity over the sensor diaphragm allows much-improved frequencyresponses to be realized. The minimum mass of the flush-diaphragm sensorresults in high insensitivity to vibration and shock inputs. Since the sensitivemember is exposed, with no mechanical protection, care in handlingmust be exercised. The asymmetry of the structural diaphragm clamp andminimized excess structural material results in a sensor design that willshow different sensitivities for pressure-induced bending in the two bendingdirections. In the case of the differential sensor, it is highly recommendedthat the device be calibrated in both pressure directions assensitivity mismatches of as much as 3% are common in asymmetricallysupportedsensor structures such as the flush-diaphragm designs as shownin Figure 1-51.The Art of Practical and Precise Strain Based Measurement 2nd Edition © 1999 CHAPTER 1-83