Definition
A pressure sensor is a device that measures the pressure, typically of gases or liquids.
Basics
A pressure sensor measures the pressure, typically of gases or liquids.
Pressure is an expression of the force required to stop a gas or fluid
from expanding, and is usually stated in terms of force per unit area.
A pressure sensor generates a signal related to the pressure imposed.
Typically, such a signal is electrical, but it might also include
additional means, such as optic signals, visual signals and/or auditory
signals.
Pressure sensors are used in numerous ways for control and
monitoring in thousands of everyday applications. Pressure sensors can
be used in systems to measure other variables such as fluid/gas flow,
speed, water level, and altitude. Pressure sensors can alternatively
called pressure transducers, pressure transmitters, pressure senders,
pressure indicators among other names.
Pressure sensors can vary drastically in technology, design,
performance, application suitability and cost. A conservative estimate
would be that there may be over 50 technologies and at least 300
companies making pressure sensors worldwide.
There are also a category of pressure sensors that are designed to
measure in a dynamic mode for capturing very high speed changes in
pressure. Example applications for this type of sensor would be in the
measuring of combustion pressure in an engine cylinder or in a gas
turbine. These sensors are commonly manufactured out of piezoelectric materials like quartz.
Some pressure sensors function in a binary manner, i.e., when
pressure is applied to a pressure sensor, the sensor acts to complete
or break an electrical circuit. Some speed cameras use them. These
types of sensors are also known as a pressure switches.
Types of fluid pressure measurements
Pressure sensors can be classified in term of pressure ranges they
measure, temperature ranges of operation, and most importantly the type
of pressure they measure. In term of pressure type, we can categorize
them in five categories:
This sensor measures the pressure relative to perfect Vacuum
pressure (0 PSI or no pressure). Atmospheric pressure, is about 100kPa
(14.7 PSI) at sea level. Atmospheric pressure is an absolute pressure.
This sensor is used in different applications because it can be
calibrated to measure the pressure relative to a given atmospheric
pressure at a given location. An example of gauge pressure would be a
tire pressure gauge. When the tire pressure gauge reads 0 PSI, there is
really 14.7 PSI (atmospheric pressure) in the tire.
This sensor is used to measure pressure less than the atmospheric pressure at a given location.
- Differential pressure sensor
This sensor measures the difference between two or more pressures
introduced as inputs to the sensing unit. For example, measuring the
pressure drop across an oil filter. Differential pressure is also used
to measure flow or level in pressurized vessels.
This sensor is the same as the Gauge pressure sensor except that it
is previously calibrated by manufacturers to measure pressure relative
to sea level pressure (14.6 PSI).
Different technologies used in making pressure sensors
This technology uses the properties of fiber optics to affect light
propagating in a fiber such that it can be used to form sensors.
Pressure sensors can be made by constructing miniaturized fiber optic
interferometers to sense nanometer scale displacement of membranes.
Pressure can also be made to induce loss into a fiber to form intensity
based sensors.
This technology uses the mechanical properties of a liquid to measure its pressure. Such as, the effect of pressure on a spring system and the changes of compression of spring can be used to measure pressure.
This technology makes use of the changes in resistance that some
materials experience due to change in its stretch or strain. This
technology makes use of the change of conductivity of material when experiencing different pressures and calculates that difference and maps it to the change of pressure.
- Semiconductor Piezoresistive
This technology uses the change in conductivity of semiconductors due to the change in pressure to measure the pressure.
- Microelectromechanical systems (MEMS)
This technology combines microelectronics with tiny mechanical
systems such as valves, gears, and any other mechanical systems all on
one semiconductor chip using nanotechnology to measure pressure.
- Vibrating elements (silicon resonance, for example)
This technology uses the change in vibration on the molecular level
of the different materials elements due to change in pressure to
calculate the pressure.
This technology uses the change of capacitance due to change of the distance between the plates of a capacitor because of change in pressure to calculate the pressure.
Applications
There are many applications for pressure sensors but we can narrow them down to two major categories:
This is the direct use of pressure sensors to measure pressure. This
is useful in weather instrumentation, aircraft, cars, and any other
machinery that has pressure functionality implemented.
This is useful in aircraft, rockets, satellites, weather balloons,
and many other applications. All these applications make use of the
relationship between changes in pressure relative to the altitude. This
relationship is governed by the following equation:
-
This equation is calibrated for an altimeter,
up to 36,090 feet (11,000 m). Outside that range, an error will be
introduced which can be calculated differently for each different
pressure sensor. These error calculations will factor in the error
introduced by the change in temperature as we go up.
Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)
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