I need some help on my train of thought. I'm reading values from a MAP sensor off my car and converting it to psi (pounds per square inch). I want to conpensate for atmospheric pressure loss when in higher altitude. I'm going to include a bmp085 atmospheric sensor to determine the pressure at the current altitude, then subtract it from 14.7psi. The difference would then be subtracted from the MAP sensor psi value that I get. Can someone confirm this.
Example:
Engine with 5psi turbo.
MAP Sensor reads 19.7psi at sea level
Atmospheric pressure reads 14.7psi
MAP sensor reads 19.7psi at 1000ft
Atmospheric pressure (bmp085) reads 14.17psi
Subtract 14.17psi from sea level (14.7) which is a loss of .53psi
Next subtract .53 from 19.7psi to give the actual boost of reading of 19.17psi @ 1000ft
If I'm reading this correctly, you are building an electronic boost controller for your turbo-charged car? Is this a gasoline or diesel powered engine?
Based on your calculations, you are trying to maintain a 5psi differential pressure in the manifold. A simple mechanical waste gate can do this already or use a differential pressure sensor and save yourself the hassle of doing calculations between two sensors.
Given the option, I would not want to artificiality limit my boost at altitude, but I live in the mountains and drive a turbo diesel that can handle twice the boost that it is currently making.
Not a boost controller. Just a digital boost gauage to read from the MAP sensor but from my readings, some suggest correction with the atmospheric pressure.
If it's not needed, then I dont have to include it. I think most boost gauges on the market dont have it... maybe because it's not needed since its only for displaying boost values.
Roger that. My boost gauge is mechanical and referenced to the surrounding air pressure. (Differential pressure) Being that you are trying to incorporate a second sensor and subtract out pressure from the MAP, I would simply use a conventional differential pressure sensor and directly read the manifold pressure, thus saving you the effort of doing the math.