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Oasis-Knowledge
Sensors
BMP-280: Atmospheric Pressure
Introduction
The BMP-280 is an absolute atmospheric pressure sensor, measuring pressure relative to a perfect vacuum with zero pressure. This means all pressure readings are positive, unaffected by atmospheric pressure changes, and yield more precise data. Pressure can be read in different units, but the most common units are Pascals (Pa), pounds per square inch (psi), bar, torr, atmosphere (atm) and their standard like milli and kilo. At any spot in earth’s atmosphere, the surrounding gas pushes down onto everything below that point due to gravity (gas has mass!) Standard pressure is defined at sea level (zero elevation), where all of earth’s atmosphere presses down on objects, where 1 atmosphere = 101.325 kPa = 1013.25 millibar = 760 torr = 14.7 psi.
The BMP-280 is a high quality sensor with ±1 hPa absolute accuracy, and ±1.0°C temperature accuracy. It can even be used as an altimeter measuring altitude, because pressure changes with altitude and the measurements are so precise. In general, pressure measurements are useful for weather forecasting, cabin pressure in airplanes, and pressure monitoring of other sealed or semi-sealed systems.
Sensor Working Principle
The BMP-280 is a piezoresistive pressure sensor, also known as a strain-gauge pressure sensor. These sensors use a conductive material which changes electrical resistance when stretched, and the change in resistance is converted to a measurable output signal. In principle, the resistance of a conductive material is proportional to its length, and stretching longer increases resistance. Resistance also increases from stretching as the cross-sectional length of the material is reduced. In conducting and semiconducting materials, strain affects the inter-atomic spacing and ability of electrons to flow from atom to atom, creating an outsized change in resistance that can be much larger than simple length and cross-sectional resistance changes. In particular, materials like platinum and nickel, and especially semiconductors like germanium and silicon, have large piezoresistive properties. Since pressure is defined as force per unit area, pressure sensors can relate deformation of a pressed-upon diaphragm or membrane to the resulting change in resistance of an incorporated material. The BMP-280 uses a porous silicon membrane to take advantage of the powerful piezoresistive effect.
Sources
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