# vacuum/boost sensor

So I got a few mpx4250gp sensors from FreeScale semiconductor as samples to play with. They are supposed to be rated at 0-250kpa sensors.

Now, to me, as I understand it:

100 kpa = atmospheric pressure at sea level
<100kpa = vacuum
250>x>100kpa = boost pressure up to 1.5bar or ~22psi boost

I emailed FreeScale to ask about their 4250gp sensor being able to measure vacuum and they said no. I do not understand how a sensor can be a 0-250kpa sensor and not read vacuum if 0kpa is vacuum. The sensor w/ power should sit at 100kpa if you’re sitting at sea level. My car currently uses a GM 3bar map sensor which allows for both vacuum and boost reading. The issue with the way it works is that the first bar on the sensor is used for vacuum metering and the remaining two bars are for boost allowing up to 28psi boost pressure to be read. That would make this a 300kpa sensor or 3bar.

So, are the FreeScale people wrong (I doubt they are), or is there some other sensor that I should be looking into using? I want the ability to measure 20inhG vacuum and up to 3bar of positive boost pressure. I do not yet have a prototyping board that I can hook this mpx4250gp sensor up w/ to test if it reads vacuum… but I would ASSUME that it will read vacuum. Someone please help w/ answers. I would very much appreciate it.

Look up the difference between gauge pressure and absolute pressure sensors.

You have a gauge pressure device that compares a sensing pressure line to your local barometric pressure. A absolute pressure gauge has a sealed evacuated lead so that the sensing line is measuring the absolute pressure relative to the vacuum sealed lead.

Lefty

So the mpx4250a would do the trick for measuring vacuum AND boost?

So the mpx4250a would do the trick for measuring vacuum AND boost?

Yes, that sensor has a total range of 2.9 to 36.3 psi absolute where 14.7psia would represent the equivelent of zero psig.

Lefty

what sensor do i need to buy to conect it wth the turbo line of my car

with low fault and no multipliers at 50 to 130. celcius

thanks