Designing Embedded Hardware, 2nd Edition

Pressure Sensors

Now let's take a look at pressure sensors. The most obvious use of these sensors is in measuring air pressure for weather monitoring and prediction. But pressure sensors are also used in cars to measure manifold pressure, in washing machines to measure water levels, and in biomedical applications such as measuring blood pressure. Another application of pressure sensors is to measure altitude, since air pressure changes with height above sea level. Ocean depth can similarly be measured.

When using pressure sensors, the substance you are measuring can adversely affect the device. Remember that these are sensitive electronic components, and fluids or corrosive gases can destroy them. So unless you're measuring clean, dry air, you'll need to provide some degree of environmental protection for your sensor. Just how you do that really depends on what the application is, what environmental conditions you must protect against, and how far your budget stretches.

Pressure sensors work by measuring the deflection of a diaphragm separating two chambers. One chamber is exposed to the pressure that is being measured, while the other chamber holds a reference pressure. The pressure difference between the two chambers causes the diaphragm to deflect, and this deflection is converted into a voltage that is proportional to the pressure difference. Pressure sensors come in three types: absolute , differential , and gauge .

In an absolute pressure sensor, the reference chamber is sealed. ...