If you are assuming perfect 1 bar atmospheric pressure with respect to absolute pressure then you could say the sensor would read -1 bar with respect to atmospheric pressure. It is better to be relative to absolute pressure (hence the name Manifold Absolute Pressure sensor) as atmospheric pressure varies depending on altitude and environmental conditions.
Something to note, absolute zero wont give you a reading of exactly zero and 3 bar (w.r.t. absolute) wont be 5V. This is because the extreme regions 0V or 5V are left out of the normal operating voltage range so that if the analogue to digital converter (in the ECU) returns a value indicating the sensor voltage is at or close to 0V or 5V then the ECU assumes the sensor must be in fault (e.g. short or open circuit) and then handles the fault appropriately.
The only true way to determine the voltage v.s. pressure is of a particular MAP sensor is to get hold of the datasheet for the sensor from the manufacturer.
Sat, 23 July 2005 11:38
