Pressure and temperature data are transmitted across a 12-bit digital interface instead of an analog line — for the first time in Bosch's SMP product line. This digital barometer's pressure signal tolerance over its lifetime is less than 1.0 kPa; Bosch claims that this is the best accuracy currently available in the market. The SMP480, which features a ten-pin premold SMD housing and is RoHS-compliant, is already being delivered in large quantities.
The core of the SMP480 is its sensor element. This is made up of a monocrystalline silicon membrane – manufactured using the advanced porous silicon membrane (APSM) process – which hermetically seals a reference vacuum. Four strain gages are implanted in the membrane in a bridge circuit. Changes caused by atmospheric pressure in the curvature of the membrane, even those measuring just a few thousandths of a millimeter, are converted into an electrical signal. Signal conditioning and A-D conversion are performed by an ASIC adjacent to the sensor element within the housing.
Barometric pressure sensors are a key component in engine management for diesel and gasoline engines. They are designed to measure the current ambient pressure accurately and with low drift. Atmospheric pressure is a function of height above sea level as well as of weather conditions. The engine management system uses the sensor measurement data to ensure the optimum air-fuel mixture, irrespective of whether the vehicle is traveling along a coastal road or a road up in the mountains. The benefit of this constant rebalancing of the mixture ratio is that it reduces fuel consumption as well as emissions of CO 2 and other pollutants.