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EEVblog #177 – Baby Scale Calibration
Posted on June 10th, 2011 15 commentsWhat does every 4 week old baby need? A visit to a NATA certified calibration laboratory, that’s what!
Dave takes his baby scales to a NATA cal lab to check it’s performance, because, well, he can…
Check out http://www.triosmartcal.com.au15 responses to “EEVblog #177 – Baby Scale Calibration”
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The accuracy available in cheap digital measuring devices these days is amazing. The self-calibration really works. Another good example is tire pressure gauges. A $5 digital tire pressure gauge will be more consistently accurate than a $50 analog gauge, and will be so even if dropped and abused.
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Simon June 11th, 2011 at 02:18
Heh, the paranoid guy in me thinks, that the scales is biased towards full kilos. What does it show when putting 1001g on it?
Bye,
Simon-
f4eru June 11th, 2011 at 05:38
It has a 10g resolution.
But i’m still impressed by the <0.1% error at full scale.For info, I used a kitchen scale for the baby, and then an adult scale.
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If you watch the highres video, you can sure see that it jumps by 5 grams. But nice take there.
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assuming the scale was made (and calibrated) somwhere in china or taiwan
we can use the local gravity difference between sydney and taipei as an estimate…
so: (12 * 9,797) / 9,79 equals 12,0086 wich at 10gram resolution makes it pretty much spot on at 12kg as well (from the scales point of wiew at least.) (unless the manufacturer used trim weights when calibrating) -
Peter June 11th, 2011 at 11:01
This is a nit-pick, especially at this sort of resolution, but the standard weights really shouldn’t be handled with bare hands. Leaving a fingerprint on the standard changes the mass. As I said, it’s nit-pick, but I do this for a living too.
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FreeThinker June 11th, 2011 at 22:14
Well you really DIDN’T do a calibration just an accuracy check, to calibrate you need to enter calibration mode (with a sequence of key presses or operating a secret switch) Then you set zero and add standard weights as directed to map set points. Save and reboot, done
.Yep I know I’m being Anal but Sagan needs to be taught Precision in everything if you want to maintain standards Lol.-
Correct, it was just a calibration check. And as it turns out it was spot on (not fussed with the 12kg range), so there was no need for a calibration adjustment.
For those interested in more on calibration:
http://www.eevblog.com/2009/08/21/eevblog-26-multimeter-counts-accuracy-resolution-calibration/
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FreeThinker is absolutely correct (and precise!). We performed a verification. And it really wasn’t a valid verification either because we did not have the accuracy specification or count error of the scales to work to. But hey!! It was great fun and when all those zeros appeared who really cares what the specification was!! PLUS.. baby Sagan is a lot better looking than Dave (must take after his mum)…. And to guy with the gloves comments on You Tube – no sticky donuts eaten before the test, it’s obvious why I avoid them
and the weights are a general purpose working set that we use both inside and outside the lab when we do on-site calibrations. They are very shiny though don’t you think!-
In precise reference standard metrology, yes, you need to wear gloves and take great care with the highest class reference weights.
http://www.troemner.com/weights_OIML.php
But the ones we used would be lower class reference weights for field use as Charles said, orders of magnitude better than what we needed!
Got any data on that set Charles?
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PS on the resolution topic… If you watch carefully you will see that the resolution is 5g up to 9.995kg and at 10.000kg it went to 10g which is of course less that the weight of a dirty diaper/nappy (whatever part of the world you are reading this from).
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FreeThinker June 12th, 2011 at 00:20
Correct! Much lessthan the weight of a dirty Nappy…Much Much less!!!
)
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Sounds like ‘yer man’s from Northern Ireland, (God’s Own Country).
Dave, how much did you pay for the scales?
Nial.
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Sorry Charles, didn’t read all the comments or would have replied directly.
So I would.
Nial.
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JRR June 11th, 2011 at 00:03