Hey Holly!

Bart's right: the current pressure sensor is located deep within the
rocket's avionics module. It's certainly not an airtight airframe, so we
do actually measure external pressure, but you're right that it's
complicated by all sorts of things.

The big problem we have right now is that we're not sure what pressure
sensor we're going to use. They're all pretty terrible. We have one in
mind right now, and we even have a sample, but the data sheet doesn't
tell us what happens when we get to near vacuum. What we'd like to do is
to take a data set in a bell jar (vacuum chamber), and then figure out
if the sensor is (1) usable and (2) useful in near vacuum.

If you want out help out with the data collection, that's great, I'll
hook you up with someone in the avionics side of things (Maria? you
game?) to do the electronics end of things. If not, let us know and
we'll try and get the data to you as soon as we can so that you can use
the data in your model. Note that we have to do this test anyway, to see
if we can use this pressure sensor on the recovery node in the rocket,
so it's high priority anyway.

The data from the physical device will be a relatively low speed (10
Hz?) data stream of analog to digital conversion values of the voltage
coming out of the sensor. The ADC will probably be 12 bits, so values
from 0 to 2^12. And the data will most like be streaming over USB, but
you won't have to worry about those details.

Finally, Tim has done quite a bit of work on atmosphericy things. See:

http://psas.pdx.edu/RocketScience/PressureAltitude_Derived.pdf
http://psas.pdx.edu/RocketScience/PressureUnits.pdf

These should get you on your way as well. And as always, I'll encourage
you to drop by a Wednesday meeting to chat about these things directly!

Andrew

Holly Grimes wrote:
> I have been looking at the projects suggested for new members, and I would 
> like to work on building an accurate model of a pressure sensor.  I have a 
> few questions about this project.  Where is the pressure sensor located on 
> the rocket?  It is measuring the pressure on the cone of the rocket, or some 
> other pressure.  What will the interface be like for the sensor?  Are there 
> any other details I should know before working on this model?
> 
> Thanks,
> 
> Holly Grimes
> 
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-- 
-------------------------------------------------------
Andrew Greenberg

Portland State Aerospace Society (http://psas.pdx.edu/)
[EMAIL PROTECTED]  P: 503.788.1343  C: 503.708.7711
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