Pressure sensor
From Wikipedia, the free encyclopedia
A pressure sensor measures the pressure, typically of gases or fluids. 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 have particular utility for monitoring the pressure in a fluid network. As compared with flow sensors, pressure sensors often require less cost to achieve a similar result. Pressure sensors are often fabricated using thin membranes that flex under pressure.
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 electical circuit. Some speed cameras use them.
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[edit] Types of Fluid Pressure Measurements
Pressure sensors can be classified in term of pressure ranges they measures, temperature ranges of operation, and most importantly the type of pressure they measurer. In term of pressure type, we can categorize them in five categories:
- Absolute pressure sensor
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.
- Gauge pressure sensor
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.
- Vacuum pressure sensor
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, if we need to know the difference of the pressure of some fluid going in a pressure boosting unit and the output pressure of that unit in a way to monitor how much we boosted the fluid pressure; we use differential sensor.
- Sealed pressure sensor
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).
[edit] Different Technologies Used in Making Pressure Sensors
- Fiber optic 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.
- Mechanical deflection
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.
- Strain gauge
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.
- Variable capacitance
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.
[edit] Applications
There are many applications for pressure sensors but we can narrow them down to two major categories:
- Pressure sensing
This is the direct use of pressure sensors to measure pressure. This is useful in weather instrumentation, aircrafts, cars, and any other machinery that has pressure functionality implemented.
- Altitude sensing
This is useful in aircrafts, 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.
