Accuracy of digital ???

Two questions:
Is a digital meat thermometer more or less accurate than a bi-metal thermometer (assuming I've calibrated the bi-metal thermometer).
Is a digital tire pressure gauge more or less accurate than a non- digital?
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"martin lynch" wrote in message

Maybe,maybe not. How much do you want to spend? The difference is likely unimportant in these applications. The advantage of digital is that it is nearly instantaneous in the case of a meat thermometer. The advantage of a digital tire gauge is that it is easier to read, rather than being more accurate but I have found that it is harder to get a good reading so going back to a mechanical pressure gauge was a relief,
An example is a digital indoor/outdoor thermometer that has a resolution of 0.1 degree C but an accuracy of +/- 2 degrees C. Enough to decide whether a bird dies of hypothermia vs thirst. The "resolution" is misleading. It implies that one could read to something in the order of +/- 1 digit (or +/- 0.1 degrees) which is pure BS.
Don Kelly cross out to reply
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Sorry, I should have clarified. I wasn't referring to resolution. More to the scenario where a reading is significantly inaccurate, say, a pressure gauge is 20 psi off, or a temperature gauge is 20 degrees off.
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It is all in the sensor being used and the accuracy/calibration of that.
Digital just relates to you what the sensor is reading. It could just as well be analog. Actually many sensors ARE analog and that data is converted to digital.
Anyway you could have a digital display reading a cheap inaccurate temperature sensor and the readings would be inaccurate. Or the same display could read a highly accurate sensor and be spot on. But a very accurate "scientific" sensor alone might be $150.00
http://www.scientificinstruments.com/tempsensors.html
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On Sun, 8 Apr 2012 15:57:14 -0700 (PDT), martin lynch

This is the classic question of accuracy vs precision.
A digital gauge can give you an inaccurate reading precise out to 3 decimal places.
For the most part I see digital instruments as being a scam, cheap parts giving bad readings with the illusion of accuracy where a good analog gauge would be better but it simply costs more.
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said

This is one of the funniest statements I've read in long time! ;-D

So true.
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On Sun, 8 Apr 2012 15:57:14 -0700 (PDT), martin lynch

If that's all you know, digital vs. non-digital, then you would have to assume the digital is probably more accurate. The non-digital implies mechanical sensing and readout, which brings with it friction caused errors (hysteresis) which can be large (think typical cheap tire guage) or smaller (dial gage type). On the otherhand, digitial probably uses sensors and readouts with none of those errors.
dave y.
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That might sound right if you never saw an electrical component change value. That is particularly true when that part is made to a price point, not to any particular spec.
I do water sampling for the state, they gave us some $800 digital meters to replace the old reagent based testing we used. They have been nothing but trouble, you need to recalibrate them every time you use them and the calibration might drift 10-15% in an hour.
How often was your digital tire gauge calibrated? How about that digital meter? The accuracy of a digital meter is just an illusion, particularly if it hasn't been calibrated recently.
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On Tue, 10 Apr 2012 18:53:28 -0400, snipped-for-privacy@aol.com wrote:

It sounds like your company just bought some crappy instruments, relative to what you had before. Slapping a digital readout on a piece of crap doesn't make it precision measurement device. Also it sounds like you're doing a chemical test of some type, which is way outside the experience I've had in a mechanical test lab setting, so maybe I'm totally not understanding your world.
I was considering, as the question posed, the problem of measuring tire pressure, and how the accuracy of a mechanical measurement mechanism would compare with an electronic sensor/display system. Sure, the electronics could be junk, but knowing nothing upfront except digital vs. non-digital, you have to go with the percentages.
dave y.
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On 10/04/2012 5:24 PM, dave y. wrote:

Please note that there is an electromechanical "non-digital" transducer in the "digital" meter. The analog signal is then digitized and displayed with a nice easy to read display.
1)Is this more accurate per $ spent than the old fashioned purely mechanical device? 2)What accuracy is good enough? 3)How convenient is it to use? )4How does the balance between accuracy and ease of use affect cost?
My personal experience with a digital tire pressure meter vs a mechanical analog meter has been in favour of the analog meter.
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Don Kelly
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wrote:

I wonder how much of this is subjective. I know in my case I've got three or four 'pencil' style tires guages and they all read something different. I only have one digital tire guage and I tend to believe it's accurate, but it's not like I've ever tested any of these aganst a standard, so who knows which one is better.
All I'm saying is mechanical mechanism based sensors and readouts tend to have hysteresis errors larger than you'll find in digital systems. And if you look at spec sheets you can easily get digital systems an order of magnitude more accurate than analog.
dave y.
p.s. I thinking of mechanical as things like a bellows driving a rack and gear that in turn moves a pointer, or a spring loaded piston, stuff like that. I'm not including things like strain gage transducers that can be quite accurate, but are not 'mechanisms'.
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On 11/04/2012 3:09 PM, dave y. wrote:

With the one "digital" tire gauge that I have had, I had more variation in results from repeated measurements than I did with mechanical gauges and, contrary to your experience, have had reasonable agreement between different mechanical gauges. The main problem with either is simply getting the gauge on the valve correctly but the mechanical gauge seemed to be less affected. Yes, I admit this is subjective.
Strain gauges or piezoelectric devices do involve some mechanical action or distortion and, as such, do have hysteresis. Simply put, all they do in comparison to "purely mechanical" devices is that the output is electrical, rather than visually mechanical. That is why I include them in mechanisms. In addition, the gauge itself is an analog device-nothing digital about it. The digital part of the instrument is the electronics used to sample the analog signal and present it in a digital form. This inherently adds some error from sampling and the bits/sample.
The difference between analog and digital instruments comes down, not so much, accuracy per $ but application ease and flexibility of the digital instruments. The digitizing is now simple and cheap so the digital side of the instrument can be excellent - so that what limits accuracy is the sensor which is inherently analog- the quantities we want to measure don't take discrete steps from one level to another.
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