Pressure Transducer Linear algorithm needed

Jul 18, 2006 5 Replies
W

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 3200 610 3100 591 3000 570 2900 550 2800 532 2700 514 2600 495 2500 476 2400 456 2300 437 2200 417 2100 398 2000 380 1900 360 1800 341 1700 322 1600 302 1500 284 1400 265 1300 246 1200 227 1100 208 1000 190 900 171 800 152 700 134 600 115 500 98 400 79 300 60 200 42 100 27.5 98 27.2 96 26.8 94 26.5 92 26.2 90 25.8 88 25.5 86 25.2 84 24.8 82 24.4 80 24.1 78 23.8 76 23.5 74 23.1 72 22.8 70 22.5 68 22.1 66 21.8 64 21.5 62 21.2 60 20.9 58 20.6 56 20.2 54 19.9 52 19.6 50 19.3 48 19 46 18.7 44 18.4 42 18.2 40 17.8 38 17.5 36 17.2 34 16.9 32 16.7 30 16.4 28 16.3 26 16 24 15.8 22 15.7 20 15.6

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M

http://80.35.195.131/ng/ng_20060718A00.png That is quite linear, isn't it?

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H

Your can do i with a polynom:

MiscEl can calculate the coefficeints:

formatting link

or a table (MiscEl can also generate a table).

Link to program:

formatting link

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J

View in Courier: +------+ +------+ +-----+ +-----+ +-----+ +---------+ | XDCR |---| GAIN |---| ADC |---| LUT |---| DAC |---| DISPLAY | +------+ +------+ +-----+ +-----+ +-----+ +---------+
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S

Fitting a simple quadratic polynomial to your data yields:

P = 5.621655 * Vin - 0.00047733 * Vin^2 -56.02

...and gives an answer that's within +/-12 psi over the range.

(+/- 0.35% FS)

Your data looks a mite "noisy" to me. Perhaps better measurements could yield a better fit.

Best regards, Spehro Pefhany

"it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
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S

What IS the accuracy of your pressure standard? As I remember from doing those things this part has to be at least 5-10 times more accurate than the calibrated transducer. So in my case it was ordered from manufacturer for placing at precisely measured gravitional force in the test group building (6-7 digits). This was THE standard from which other standards (mobile) were compared. Also the precise zeroing of output at start of calibration and its stability over time is very important. Then comes the transducers full scale and its +/- FS error promissed by manufacturer. Readings

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