Abstract:
The use of extremely miniature silicon piezoresistive pressure sensors have come into wide use in recent years. The sensors realized by microelectronic techniques, along with a Wheatstone bridge configuration, present advantages in size, sensitivity, and linearity of electrical response. As a result, these qualities are valuable for pressure measurements on a rotor blade. In-house rotor testing involves the study of Mach scaled rotor blades operating up to high advance ratios (μ=1.5). The surface pressure data from the sensors at specific radial and chord-wise locations are integrated to obtain pitching moment, lift and chord force. Currently, two pressure transducers, Kulite and Endevco, are used in blades for testing on hover stand and in wind tunnel experiments. Through systematic bench top calibration, it was shown that the Endevco and Kulite sensors performed identical in their phase and magnitude response up to a bandwidth of 250 Hz. Because Endevco sensors do not come pre-calibrated to compensate for temperature effects, simple passive methods were explored to conduct thermal calibration and remove temperature sensitivity. In this manner, cost-effective pressure sensor solutions were achieved using the Endevco sensors that are about 1/20th the price of a Kulite sensor. Finally, the Endevco sensors were subjected to centrifugal loading in a vacuum chamber and it was determined that the centrifugal effects on pressure output were negligible. Experiments are being conducted to quantify the electrical response of doped p-type silicon resistors to heating and cooling, and consequently the gauge factor of the Endevco piezoresistor pressure transducer are being determined in an effort to streamline the temperature calibration process.