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
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The capacitance pressure transducer has the attractive features of other diaphragm transducers , including small size and a wide operating range . Many common and inexpensive pressure transducers use this measuring principle and are suitable for many engineering measurement demands , including a niche as the on-board car tire pressure sensor of choice .However , the principle is sensitive to temperature changes and has a relatively high impedance output . If attention is paid to these shortcoming, an accurate and stable transducer can be made.
Piezoelectric Crystal Elements
Piezoelectric crystal elements form effective elements for dynamic (transient) pressure measurements. Under the action of compression, tension, or shear, a Piezoelectric crystal deforms and develops a surface charge q , which is proportional to the force acting to bring about the deformation. In a Piezoelectric pressure transducer ,a preloaded crystal is mounted to the diaphragm sensor , as indicated in figure 9.14. pressure acts normal to the crystal axis and changes the crystal thickness t by a small amount บอกสูตร
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 the capacitance pressure transducer has the attractive features of other diaphragm transducers , including small size and a wide operating range . Many common and inexpensive pressure transducers use this measuring principle and are suitable for many engineering measurement demands , including a niche as the on-board car tire pressure sensor of choice .However , the principle is sensitive to temperature changes and has a relatively high impedance output . If attention is paid to these shortcoming, an accurate and stable transducer can be made.
Piezoelectric Crystal Elements