Piezoelectric Pressure Sensors
Crystals are elastically deformed when they are exposed to pressures around a particular axis. There is a flow of an electric charge for a few seconds by electric potential due to deformation. The deformation experienced by the crystal due to pressure acts on the sensing diaphragm which generates an electrical signal is proportional to the amount of force applied. An acceleration compensator is also provided because the crystal can also be deformed by acceleration.
It can't measure the static pressures for a long time, but can measure shock;
vibration; pressures associated with blasts, explosions, or pulsation; or the
dynamic conditions in rocket motors, engines, compressors, and etc. The
The advantages of these sensors include
their small size, rugged construction, high speed of response, and
self-generated signal.
They have limited to dynamic measurements, are sensitive
to temperature variations, and require special cabling and output signal
amplification.
Magnetic Transducers
Magnetic transducers are mainly induction and reluctance type by utilizing magnetic principle in converting the elastic movement of a sensor into an electric signal. There is a change in inductance and reluctance, as the pressure sensors cause a movement.
Inductance is the property of an electric conductor that causes electromotive force (EMF) to be generated for a given rate of change of current flow in the circuit. Reluctance is the property of the magnetic circuit opposing the passage of magnetic flux.
In Inductive elements, the process pressure moves inside the magnetic iron core inside a coil, which alters the self-inductance of the coil. The inductance of the coil increases, as the core is pushed into the solenoid. Though there is a change in the inductance ratio of the two coils, core movement is detected. The eddy current causes variations in impedance, while the transducing element remains constant.
In reluctive elements, a magnetic vane changes the gap in the magnetic flux path of both cores as it moves. The result of the motion of the magnetic vane is a change in the inductance of the two coils (L1 and L2) as magnetic reluctance varies with the size of these gaps.
Optical Transducers
The process pressure moves the diaphragm sensor, which lifts the vane in front of an infrared light beam, the amount of light affected
on the measuring diode varies.
For other electronic pressure sensors or transducers follow the link: Instrumentation Basics: Electronic Pressure Sensor Basics I (instrumentbasics.blogspot.com)
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