Capacitance Element
Another common method to convert diaphragm displacement to a measurable signal is a capacitance sensor. One version uses a thin metallic diaphragms as one plates of a capacitor paired with a fixed plate to complete the capacitor. The diaphragms is exposed to process. When pressure changes, so as to deflect the diaphragm, the gap between the plates changes, which causes a change in capacitane.
To illustrate this, a tranducer using this method is depicted in Figure 9.13. The capacitance C developed between two parallel plates separated by average gap t is determined by
Where the product ∁ϵ is the permittivity of the material between the plates relative to a vacuum (ϵ=8.85×〖10〗^(-12) F/m; c=dielectric constant), and A is the overlapping area of the two plates. The dielectric constant depends on the material in the gap, which for air is c=1 but for water is c=80. The capacitance responds to an instantaneous change in the area-averaged plates gap separation from which the time-dependent pressure is determine. However, the capacitance change is small relative