Convert A/D result to pressure

Archiver

>I've got a 12 bit A/D which is getting 0-4 volts from a pressure
>sensor. I want to display the pressure from 0 - 30 PSI but am
>having some problems with the conversion formula. Do I multiply the
>reult by .976 milivolts? If so how is that done. Thanks in advance!

That would give you millivolts. More likely you will want psi
directly, so multiply times 0.0073242 (=30psi/4096 counts). Probably
also you want the result calculated in units of 0.01 psi, or better.
That means multiply the raw count times 0.73242. In Stampese that is:
psi100 = rawCount ** 48000
debug psi100/100,".",dec2 psi100,cr


(ratio for **: 48000/65536 = 3000/4096)


-- best regards
Thomas Tracy Allen PhD
electronically monitored ecosystems
http://www.emesystems.com
mailto:tracy@e...

Archiver

I've got a 12 bit A/D which is getting 0-4 volts from a pressure sensor. I
want to display the pressure from 0 - 30 PSI but am having some problems with
the conversion formula. Do I multiply the reult by .976 milivolts? If so how
is that done. Thanks in advance!


[noparse][[/noparse]Non-text portions of this message have been removed]

Archiver

In a message dated 2/28/02 3:40:39 PM Central Standard Time,
ricky@m... writes:


> I've got a 12 bit A/D which is getting 0-4 volts from a pressure sensor. I
> want to display the pressure from 0 - 30 PSI but am having some problems
> with the conversion formula. Do I multiply the reult by .976 milivolts?
> If so how is that done.

There are two operators that allow you to multiply by fractional values --
but both return integer results. If you multiply the result by 9.76 (tenths
of millivolts) that's what the units result value will be. Here's a quick
demo of both operators.

a2d var word
result var word

a2d = 4095
result = a2d */ $9C2
debug dec result / 10000, ".", dec4 result, cr, cr

result = (a2d * 9) + (a2d ** $C49C)
debug dec result / 10000, ".", dec4 result


The star-slash operator multiplies by units of 1/256; the star-star operator
multiplies by units of 1/65536. I personally find that I end up tweaking the
*/ or ** parameter to give the best results based on test input. This, of
course, is affected by your desired precision.

The best practical explanation of these operators is on Tracy Allen's site.
Tracy builds very cool dataloggers with the BASIC Stamp and has solved more
of these tricky math problems than most of us will encounter.

http://www.emesystems.com/BS2index.htm

-- Jon Williams
-- Parallax






[noparse][[/noparse]Non-text portions of this message have been removed]