Help with math problem


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Topic: Science > Physics
User: "William Hightower"
Date: 23 Jul 2006 04:19:12 AM
Object: Help with math problem
Bz,
Thank you for your email and input. First let me give you a
little more
information on this project. The specification on the pressure transducer
under test is as follows:
1. 0 to 5000 psi absolute
2. +-0.25% Pressure Non-linearity
3. +- 0.75% Span Temperature Error - Span
4. +- 0.75% Span Temperature Error - Zero
5. 0.05% Span Thermal Hysteresis - Span
6. 0.05% Span Thermal Hysteresis - Zero
The numbers in the News Group message I posted where from measurement
taken under the following conditions, test setup and test equipment used:
1. Ambient pressure was 1007 mill bar or 14.6053 psi during setup and
measurements
2. Ambient temperature was 85 degrees F (29 degrees C)
2. Applied pressure of 0 psi gage to 3400 psi gage, using a manual control
valve
3. Two bourdon tube type pressure gages where used for taking readings,
0 to 100 psi gage and 0 to 4000 psi gage
4. Pressure transducer output voltage measurements taken with a RSR 705
Multimeter (3 ½ digit display, 200m V and 2V voltage ranges)
The test setup was changed after taking the 0 to 100 psi readings to use the
0 to 4000 psi gage. Other than changing the gages, all else remained the
same.
The accuracy (specifications) of the bourdon tube gages used is unknown.
Care was taken to view the gauges head on, lining up the needle with the 2
psi divisions on the 0 to 100 psi gage and the 100 psi divisions on the 0 to
4000 gage.
Testing began by applying 3500 psi to the test setup and bleeding off the
pressure to take the above mentioned readings. I found that tapping the
gauges would allow the needle to settle after bleeding off the pressure to
obtain
the next lower division to be read.
This should explain a majority of the inaccuracies in the readings posted.
Another inaccuracy could be Temperature. Through out the setup and taking of
all measurements, ambient temperature (85 F, 29 C) may have varied several
degrees plus or minus.
I will try to obtain an accurate, calibrated, digital pressure gage and have
the
Multimeter calibrated to take the next set of measurements. Hopefully this
will help.
Again, thank you for your input.
Best Regards,
Bill
----- Original Message -----
From: "bz" <bz+sp@ch100-5.chem.lsu.edu>
To: "William Hightower" <william.hightower@earthlink.net>
Sent: Wednesday, July 19, 2006 9:03 AM
Subject: Re: Help with math problem

"William Hightower" <william.hightower@earthlink.net> wrote in
news:X14vg.993$bP5.482@newsread1.news.pas.earthlink.net:

I have a pressure transducer that I am trying to make its output linear
to drive a digital readout.
The digital readout takes a voltage of 0 to 2 Volts. The problem I am
having is Cumming up with an algorithm to crunch the following numbers
to feed the digital display. Any and all help will be greatly
appreciated.



PSI Output (m volts)

3400 649
3300 629

....

0 15.6




linear
A rather good fit
y = 0.1861x + 9.4355 or
y = 5.3731x - 50.494

R2 = 0.9997

excel's 'add trendline' is sufficient to make such a fit.





--
bz

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

bz+sp@ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap


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