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

Applications Note 1-6:ical size of the sensorÕs active member. For the measurement of higher frequencies,spatial independence will require that smaller and smaller sensors beemployed in any given medium.The Nature of the Measurand:Measurands may be scalar quantities such as voltage, current, or temperature,meaning that they can be completely specified by magnitude alone. Other measurandsmay be vector quantities such as velocity, acceleration, and force, requiring adirection and magnitude to define the measurand.The effectiveness of the flush-diaphragm pressure sensor in sensing a pressureshock wave is a good example in that the wave has magnitude as well as directionand the sensor will not respond with equal outputs depending upon the angle of thewave relative to the sensor surface. In cases such as this, the sensor would alsorequire a Òfield responsivityÓ calibration in order to define the sensitivity of thedevice as a function of angle relative to a measurand input.Microphones are typically calibrated to show the field responsivity of this sensortype to measurand inputs at various angles to the sensor active member.The System Transfer Function:Bearing in mind the requirements of spatial independence, and the fact that thedefinition of the field responsivity of a sensor may also be necessary in order todefine the total response of the sensor, the transfer function of the measurementsystem is as shown in Figure 1-7.The Art of Practical and Precise Strain Based Measurement 2nd Edition © 1999 CHAPTER 1-21