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Applications Note 1-13:the sensor. The significant dead volume produced by recessing of the sensordiaphragm severely limits the frequency response of such a sensor. Thecavity over the diaphragm will act as a Helmholtz cavity or pneumatic filter,attenuating dynamic pressure inputs significantly. The recessed-diaphragmdesign provides superior mechanical protection of the sensingdiaphragm and generally superior zero stability as the cavity will also addsignificant thermal mass to the sensor, rendering the design less sensitive tothermal-transient inputs. The added structural mass of this design also providesexcellent spring member support with the diaphragm removed fromthe generally high stresses found in threaded-mounting configurations. Inmeasurement environments where compacting particles could be present,the recessed-diaphragm design may not be the most suitable, as compactionof particles over the sensor diaphragm (Figure 1-47) will reduce thesensitivity of the sensor significantly. In cleaning of the pressure port anddiaphragm, only fluid cleaning solvents and solutions compatible with thewetted materials of the sensor should be used. The use of any mechanicalcleaning tools will undoubtedly result in damage to the sensor.FIGURE 1-47. Particulate Compaction (Recessed-Diaphragm):Compacted ParticlesParticulate-Laden FlowMany other variations of the recessed diaphragm design are commonlyavailable with many process-type designs being of the filled variety wherethe active sensor is isolated from the measurand (medium) by a flexibleThe Art of Practical and Precise Strain Based Measurement 2nd Edition © 1999 CHAPTER 1-81