Thứ Năm, 26 tháng 5, 2011

Basic Tips On The Working Principles Of Pressure Sensors

By Adriana Noton


As the most used systems for pressure measurement, the pressure sensors are good for gases and liquids. The devices can be seen in action when the fluid reaches the containing limit and pushes on the elements of force detection from the equipment. This is the moment when an electrical signal is created and sent to an interpreter. This is the functioning principle on which every sensor is based.

Besides the direct indicator of how much force is released from the fluid, other additional things can be indicated. For example, the fluid level or how fast it is flowing etc. Depending of the type of detection, the devices can be categorized as static or dynamic.

During the steam age the first devices were made and they became very popular. Since then, the technology has evolved a lot, and they have adapted. Their popularity is still the same in our times. They can be split in three categories depending on how they work: variable capacitance, strain gage and piezoelectric.

These equipments can be found under various types and designs. They can be of high performance or of lower performance but cheap. They can be different because of the measurement ranges or temperature ranges. As an example of high performance pressure sensor, the dynamic devices which detect fast modifications in speed and pressure are the ones. They are built from quartz crystals (piezoelectric).

Strain gage devices are constructed from 2 parts: the diaphragm and the strain gauge. When the force created by the fluid increases, the diaphragm detects the modification and it sends a signal to the strain gauge. Now the strain gauge will resist the force. Then the resistance force generated will be measured by a Data Acquisition System or DAQ.

The variable capacitance modules have two metallic elements. The first element is a metal plate and the second is a metal diaphragm. The distance from the plate to the diaphragm determines the detection of any physical force. Like the accelerometer, devices of this construction are very stable; the only disadvantage is the resistance to high temperatures. It is also more difficult to assemble this type.

Being made of quartz crystals, the piezoelectric sensors use the properties which are owned by these crystals from nature. They have this feature that allows them to make an electrical charge when they detect a force increase. The signal created must be amplified with the proper circuitry. They are not as resistant as other materials to vibration exposure or to any type of shock.

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.

Nowadays pressure sensors have a very high range of use, they are commonly used in the food industry, for example. With no exceptions, they have the role of measuring the forces made by the fluids. They are also able to detect the flow and the fluid level.




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