What’s the difference between all the available pressure sensors and how to choose one? This is what you should consider.
There might be times, as in the COVID-19 crisis, where measuring pressures becomes a question of life and death. What is it that one must keep in mind when selecting a pressure sensor then?
In the Open Source Ventilator – Open Lung initiative we’ve faced this issue, and along the way we’ve learned many important things, let’s give a look at some of them.
There’s a wide variety of pressure sensors in the market, and there’s a reason for it: each is optimized for a specific purpose, these are the most common ones:
Note: to ease the explaination and drawings I’m going to show sensors with barbed tubing connections, they are clearly not the only ones available in the market, more later in the article.
Absolute pressure sensors are chosen each time comparison between vacuum and the system is needed. They are obtained by proceeding with the assembly of the package substrate in a high vacuum area, effectively sealing the package with a vacuum empty area inside. On the vented side, this small vacuum tank will be exposed by means of a very thin silicon diaphragm which will be slightly bent depending on the measured pressure. This effect is then measured with various techniques, one of which is by applying a strain gauge, read, decoded, and then sent to the external world. A usage example would be when measuring atmospheric pressure to compute dew points and forecast the weather. The output of this sensor is then similar to the equation: Pout(t)=Pin(t)-Pvacuum.