Method for temperature compensation of a piezoresistive gaged metal diaphragm

Abstract

There is described a temperature compensation scheme for a pressure sensitive metal diaphragm transducer. The transducer employs a Wheatstone bridge fabricated from p-type piezoresistors. The Wheatstone bridge is glassed directly onto the metal diaphragm. As the temperature of operation increases, the diaphragm exhibits a temperature variation of the Modulus of Elasticity. The Modulus of the metal diaphragm decreases with increasing temperature. Because of this, the same pressure applied to the metal diaphragm causes it to deflect further, which in turns causes increased strain applied to the bridge. Because of this effect, the sensitivity of the transducer increases with increasing temperature. A resistor is now placed in series with the Wheatstone bridge. The resistor is in series with the biasing voltage and because the TCS of the diaphragm is of an opposite sign, the series resistor has an even higher TCR in series with the bridge. In this manner, the bridge voltage is made to decrease with increasing temperature. Due to the fact that the bridge voltage decreases with increasing temperature the change in voltage compensates for the change in the Modulus of the metal diaphragm and therefore provides an accurate output at all temperatures.