Thursday, May 26, 2011

Fundamental Things About How Pressure Sensors Work

By Adriana Noton


Pressure sensors are devices that are meant for measuring the pressure. The measuring applies to any liquid or gas. When the level of substance has reached a certain limit and has even passed over it, the device translates the force generated into an electric signal. This signal is interpreted by a computer and in this way the measurement is made.

Not only the direct force can be calculated, but also other parameters will be obtained indirectly. This involves the level of fluid in the container, the speed of flowing and others. Any type of information can be provided by these readers. The measurement can be static and dynamic.

The requirement for these devices dates from steam age. Many of the equipments that were invented then are still used in our time. There are three types of these devices: piezoelectric, variable capacitance and strain gage.

The forms and design types of thesepressure sensor devices can be very different. The classification is made depending on cost or performance, the measurement range or the temperature at which they are used. The dynamic sensors can indicate when the speed and pressure are modifying. They are known as high performance devices and they are usually piezoelectric.

The strain gage systems are made of two things: the strain gauge and the diaphragm. The diaphragm detects the changing in force when the level of the fluid grows. Then the strain gauge will oppose resistance for that force, and the resistance will be calculated by a DAQ module (Data Acquisition System).

In the case of variable capacitance devices, the layout involves two metal parts: a metal diaphragm and a metal plate. These two metal parts have a specific distance between them. At the first change of the distance value, a force change is recorded. Like the accelerometer, the variable capacitance devices have a higher stability than the other device types, but they are highly sensitive when it comes to high temperatures. More, assembling them is harder than assembling the other 2 types.

The piezoelectric systems have a construction layout that is based on quartz crystals. The quartz has a natural property which makes it create electrical charges at the detection of strong forces. The signal has to be boosted after it is generated. Their disadvantage is low resistance to vibrations and shocks.

The signal obtained from the sensors is usually small and it can be measured in mV (a thousand parts is one Volt). The range of Volts that is outputted from the device is related to the amount of physical force which generates the current. For instance, zero Volts mean zero force. In this point no electrical signal is sent to the interpreter. The maximum range limit can be, for instance 5V, case in which a pressure of 5 Bars is generated.

Pressure sensors are devices that are very common in our days. They are used in many industrial domains. For example, they have a good role in the food industry. Regardless of their type, they are good tools for measuring the force generated by different fluids. But they also measure the fluid speed, the level of a fluid inside a container or many other valuable details.




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