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Mechatronics Zone
Specifying & Creating Data-Acquisition Systems, Part 2
3/6/2012

Instead of using a small portion of an ADC's input range for a sensor input, amplify the signal to better resolve it with smaller voltage steps.
Instead of using a small portion of an ADC’s input range for a sensor input, amplify the signal to better resolve it with smaller voltage steps.

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Jack Rupert, PE
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Platinum
Great Series
Jack Rupert, PE   3/17/2012 6:47:06 PM
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Thanks for a very interesting refresher article.  I hope to see more of these in the future.  It's amazing what one tends to forget when it is not being used everyday.

Jon Titus
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Re: calculation of LSB step size
Jon Titus   3/16/2012 10:39:15 AM
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Yes, Paul, and I requested this correction a few weeks ago when another reader noted the incorrect units.  Sometimes symbols don't translate well from a Word document to the HTML.  I'll ask again--thanks for your reminder.

Paul-stl
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Iron
calculation of LSB step size
Paul-stl   3/16/2012 9:47:14 AM
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1 saves
In your calculation of the LSB step size, you state that 10e-3 V /16383 steps = 0.610V.  Shouldn't this be 0.610 microVolts?

N. Christopher Perry
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Gold
Re: More good information.
N. Christopher Perry   3/8/2012 5:20:51 PM
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Ouch....  Did you track down the offending party and box their ears?

Jon Titus
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Re: More good information.
Jon Titus   3/8/2012 5:06:53 PM
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Hi, Christopher.  You make a good point about sensor ranges, so I'll put it on my topic list for a column after I wrap up this series on data-acquisition.  You remind me that it's always good to start on a high range with an instrument and then change to a lower scale as appropriate. I once saw a bent needle on a Simpson VOM someone used to measure line power with a low-voltage setting. It almost made me cry.

N. Christopher Perry
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Gold
More good information.
N. Christopher Perry   3/8/2012 4:34:38 PM
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Glad to see you presenting this.  I've often had to point this out to my junior engineers; now I can point them to this article.

On a parallel subject.  Are you going to discuss selecting sensor ranges relative to the measured value in question?  I've also encounter situations where the engineer selected something like a 0-100 psi pressure transducer to measure a varying pressure with a mean around 80 psi and then just assumed the occasional 100 psi spikes where as high as the signal got....  I was trained to select a sensor which put the nominal reading at ~50% of the sensor range if I was fairly sure of what I was measuring, and to use less of the range if there was more uncertainty in the measured quantity.

Nancy Golden
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Platinum
Great Information!
Nancy Golden   3/7/2012 5:07:21 PM
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Very nice solution for utilizing the entire range available and increasing the apparent resolution – with a very cost effective and easy to implement solution. Thanks for another great article!

Jon Titus
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Thank you
Jon Titus   3/7/2012 3:26:10 PM
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Thanks for your kind words.  The third installment covers anti-aliasing filters and it should go live in a week or so.  Stay tuned. 

TJ McDermott
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Adding to the toolbox
TJ McDermott   3/6/2012 8:47:25 PM
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I share naperlou's statement; I'm going to add this series to my library.

naperlou
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Gain
naperlou   3/6/2012 10:48:56 AM
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Jon, good article.  This is a very useful bit of informaiton for deigners to have in their toolbox.

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