One of the important factors to be considered when selecting a pressure sensor is to identify the media that will be used and to ensure that the complete construction of the sensor is able to resist them – in both the short and long term. It is very important to check each stage of compatibility with the media to ensure the long life of the pressure sensor.
In some applications the pressure media may be incompatible with the sensing element; in others it might be with some of the materials used to assemble the sensor, such as an O-ring, a brass fitting, brazing, oil, silicon, plastic etc.
It is important to be aware that some manufacturers’ specifications may be incomplete. For example, they might indicate that a sensor has a stainless-steel diaphragm, but neglect to mention that the diaphragm is fitted with an O-ring.
Consider all possibilities
Another potential problem is in failing to account for some of the side-effects that can develop in the equipment. For example, when measuring air pressure a plastic diaphragm can be used without any problems, providing the air is clean and dry. However, if there is oil or dirt present the plastic diaphragm will become contaminated over a period of time.
Alternatively, in many water pressure measuring applications the machinery has to be cleaned each week with bacteria-killing liquid that attacks everything except stainless steel. For everyday usage a lower-cost material could be used, but the sensor would have to be removed during each cleaning process or a stainless-steel sensor would have to be fitted.
Two sides to compatibility
Even if the sensor is compatible with the media, the possibility exists that the media can be contaminated by the material of the sensor. This can cause many problems, particularly in medical and other similar applications.
Finally, don’t forget to consider the consequences of accidents. What would happen if the diaphragm were to break? Is the sensor filled with oil behind the diaphragm and could this contaminate your media? Could the media short out the electronics? Could small fractures cause contamination of the media or cause the media or ruin some other equipment such as a valve, pump etc?
Always check the risks very carefully and weigh up the benefits.
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