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Different ways of protecting pressure sensors from overpressure
19th June 2007 On most manufacturers pressure sensor data sheets you will find an over-pressure or proof pressure rating. This is the maximum pressure that the pressure sensor will tolerate without damaging the diaphragm or putting it outside specification tolerances. The overpressure or proof pressure rating is mainly a guideline for determining whether a pressure sensor will be protected when there is a system failure and a pressure is applied which is over and above the normal operating conditions. A pressure sensor manufacturer can optimise over-pressure in the following ways: One design approach is to under use the range of a particular diaphragm rating e.g. use a 100 bar diaphragm to measure 50 bar effectively doubling the overpressure rating. The main drawback of this method is that the accuracy and output sensitivity are compromised so the high output and linear sensing technologies such as semiconductor strain gauge tend to be favoured when using the down ranging method.
A more complex approach is to incorporate mechanical stops behind the diaphragm to prevent the diaphragm from being over-stressed. This leads to a more expensive and bulkier mechanical design. A sensing technology that has a large enough degree of travel is also required in order to make setting the distance of the mechanical stop to the correct over-pressure rating practical. Alternatively for sensing technology that does not have a high degree of mechanical movement it can be integrated into an oil filled capsule with a non-sensing diaphragm that will yield in an over pressure condition to allow enough movement in another non-sensing diaphragm so that it bottoms out onto a mechanical stop and thus prevents any further increase in pressure and protects the sensing diaphragm. Introducing pressure relief into the pressure sensor design is another elaborate way to protect the sensing diaphragm from over-pressure. Either self activating mechanical pressure relief valves or electrically activated valves controlled by the pressure sensor output can be utilised to vent and isolate the pressure sensor from an over pressure condition.
Pressure Measurement Resource Links Convert an altitude in feet or meters to a pressure unit Convert temperature units to and from degrees celsius, fahrenheit or kelvin Explain an IP rating for ingress protection Explanations for pressure measurement terms Create a pressure sensor specification
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