RE:Barometric Pressure Sensor

[Rodney Moore <m6bigdog@xxxxxxxx>]

Andrew,
Certainly one of the more elusive Bosch DME components!!
The only information I have seen as of yet comes from information from in 
the technical information microfiche and the ETM
The barometric pressure sensor in my M6 code # 0 280 101 001 has values of:
=<880mbar = 0 ohms
=>930mbar = infinite ohms

The M6, ETM shows it sensor hooked up in a potentiometer configuration:
Reference voltage(5 volts) on pin 3
Ground reference on pin 2
Wiper on pin 1

Reference for barometric pressure:
                  STANDARD ATMOSPHERE
                       A standard atmosphere has been defined by the 
International Civil
                       Aeronautical Organization (ICAO). It assumes a mean 
sea level
                       temperature of 15 degrees Celsius, a standard sea 
level pressure of
                       1,013.25 millibars or 29.92 inches of mercury, and a 
temperature lapse
                       rate of 0.65 degrees Celsius per 100 meters up to 11 
kilometers in the
                       atmosphere.
                  STANDARD SURFACE PRESSURE
                       The measurement of one atmosphere of pressure under 
standard
                       conditions. It is equivalent to 1,013.25 millibars, 
29.92 inches of
                       mercury, 760 millimeters of mercury, 14.7 pounds per 
square inch, or
1.33  grams per square centimeter

I would assume for near sea level driving(1013mbar) the sensor would simply 
remain in the same position(full scale).  It would only be when the vehicle 
reaches a given altitude(930mbar, 27.47 inHg) that the sensor would then 
begin to respond.  I'm sure there is a standard graph(conversion table) of 
millibar vs altitude somewhere, however I don't think that would help test 
the unit.

I come up with .02954 inHg per millibar and since 1013 - 880 = 133 x .02954 
= 3.93 inHg.
So if you live at or near sea level, I believe you would need to put the 
sensor in a chamber where you could subject it to a 3.93 inHg vacuum in 
order to make the wiper move through its full range.

I hope that helps.

- -----
Rodney Moore
e-mail: m6bigdog@domain.elided

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