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

Strain-Based Measurement Introduction:As in accelerometer calibration, the gravimetric method may be usedwith broadband noise inputs, sinusoidal or discrete-frequency inputsgenerated by an electrodynamic shaker to determine the load cell transferfunction.Pressure Transducers:Pressure sensors may be calibrated by many different methods for the purposeof determining the sensor transfer function where some of these methods arediscussed as follows:Deadweight PressurePressure transducers are statically calibrated by means of the deadweighttester where calibrated masses are sequentially added to a platformthat is supported by a precision piston. The pressure is increasedmanually or automatically, by either a ram or controlled-pressure regulator,to the point where the pressure, generated by the calibratedweights acting over the area of the precision piston, is balanced and thepiston is free-floating. The precision of this type of calibration systemrelates to the area difference between the piston and bore within whichit moves. Traceable uncertainties of as low as .0004% of applied pressureare achievable with deadweight calibrators where the piston andbore are precision lapped to minimize area differences. As the area differencebetween the piston and bore results in a leakage path, it is commonfor the piston to slowly settle where the pressure will ultimatelydecay to zero. Operating procedures for deadweight pressure calibratorswill often specify that the weights be manually rotated to distributethe fluid film and minimize friction while data is collected at each inputlevel. The sensor to be calibrated is in communication with the balancedpressure reservoir and the sensor output is recorded. As with allstatic-calibration methods, phase data is not available.CHAPTER 1-34 The Art of Practical and Precise Strain Based Measurement 2nd Edition © 1999