What is the future of Endevco silicon pressure sensors, and what are their respective part numbers?
Endevco was one of the first companies to develop silicon pressure sensors. A major breakthrough came when Endevco introduced the sculptured diaphragm design that nearly doubles the sensitivity of the sensor.
The main advantage a silicon diaphragm affords is a very broad linear frequency response. Flor example, the 8511A series of pressure transducers utilize silicon diaphragms with resonant frequencies in excess of 1 MHz. This high level of resonant frequency allows the 8511A to have a linear (5%) frequency response from 0 Hz to approximately 200 kHz!
A related secondary advantage of micromachined silicon diaphragms is the ability to miniaturize a pressure transducer. Pressure transducers with stainless steel diaphragms are typically larger in overall size. The Model 8507C (Figure 1) and the Model 8515C (Figure 2) illustrate just how small these transducers can be.
Figure 1: The Endevco model 8507C measures only .099" in diameter and is designed for flush mounting.
Figure 2: The 8515C is used for surface-mount applications and measures .240" in diameter and .240 inches thick.
This characteristic also allows for the measurement of fast pressure events that have a somewhat long time history. Since these transducers can sense down to 0 Hz, they are often called "DC responding" devices.
The main disadvantage of silicon-diaphragm pressure transducers is their incompatibility with water. The diaphragms can tolerate about one week's exposure to water or to media containing water and will eventually be permeated. Once water moves through the diaphragm, it will short out the diffused Wheatstone bridge and any associated temperature-compensation circuitry, rendering the transducer temporarily non-operational. Silicon pressure transducers can be used in applications involving water, but they must be removed periodically and subjected to temperatures that will evaporate any water that has begun to permeate the diaphragm.