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Fluke accuracy ±(2%+2) - What means the +2?
2X:
--- Quote from: TimFox on March 17, 2024, 06:50:47 pm ---Go back to elementary analytic geometry (graphing).
If the relationship between the input voltage V and the display value Y is truly linear (ignoring the discrete values restriction), then its equation is
Y = m V + b
where m is the slope and b is the offset.
For that ideal case, there can still be errors in m, which can be specified in terms of fraction of reading, and b, which would be given in terms of Y, either in counts displayed or fraction of full scale.
Of course, in the practical case there are still unwanted variations about the best-fit straight line, which will increase the specification values.
--- End quote ---
Thanks for the nice example.
HKJ:
--- Quote from: 2X on March 17, 2024, 06:57:09 pm ---
--- Quote from: HKJ on March 17, 2024, 05:35:42 pm ---Display 2.000V in 6.000V range: The 0.5% is 10 and then the +3 for a total of 13, i.e. the real value is somewhere between 2.000-0.013 to 2.000+0.013 -> 1.987 to 2.017 volt.
--- End quote ---
Maybe it is obvious but could you explain me what do you mean by "Display 2.000V in 6.000V range: The 0.5% is 10 and then the +3 for a total of 13" or "Display 2.00V in 60.00V range: The 0.7% is 1.4 and then the +3 for a total of 4 (rounded down)". How arises the 10 from 0.5 and 1.4 from 0.7? In fluke's example the "+2 number" equals to 0.2 value but in yours the "+3 number" equals to 0.003 value. This value of the +Number is where mathematically I can't understand in what value corresponds. I beleive is something simple but for some reason I can't catch it. Thanks for your replies.
--- End quote ---
2.000V in 6.000V means 2V in 6V range.
0.5% is 0.5% of 2000 that is 10 or 0.010V
The +number depends on the actual resolution on the display, it is always on the last digit. i.e. if the display is 2.000 then +3 is 0.003, if the display is 2.0000 then +3 is 0.0003
J-R:
Side note, calibration data is more useful in my opinion than the published accuracy specs. Many of my Fluke DMMs exceed their spec by a factor of 10 or more, so the fact that the published specs are worse than some other brand doesn't translate to reality in many cases.
2X:
--- Quote from: HKJ on March 17, 2024, 09:04:39 pm ---
--- Quote from: 2X on March 17, 2024, 06:57:09 pm ---
--- Quote from: HKJ on March 17, 2024, 05:35:42 pm ---Display 2.000V in 6.000V range: The 0.5% is 10 and then the +3 for a total of 13, i.e. the real value is somewhere between 2.000-0.013 to 2.000+0.013 -> 1.987 to 2.017 volt.
--- End quote ---
Maybe it is obvious but could you explain me what do you mean by "Display 2.000V in 6.000V range: The 0.5% is 10 and then the +3 for a total of 13" or "Display 2.00V in 60.00V range: The 0.7% is 1.4 and then the +3 for a total of 4 (rounded down)". How arises the 10 from 0.5 and 1.4 from 0.7? In fluke's example the "+2 number" equals to 0.2 value but in yours the "+3 number" equals to 0.003 value. This value of the +Number is where mathematically I can't understand in what value corresponds. I beleive is something simple but for some reason I can't catch it. Thanks for your replies.
--- End quote ---
2.000V in 6.000V means 2V in 6V range.
0.5% is 0.5% of 2000 that is 10 or 0.010V
The +number depends on the actual resolution on the display, it is always on the last digit. i.e. if the display is 2.000 then +3 is 0.003, if the display is 2.0000 then +3 is 0.0003
--- End quote ---
This example make it very clear. Many thanks for your time and for your help.
So If theoretically we have a multimeter with specs ±(0%+4) in range of 60.00V & in range of 100.0V:
if we measure a 10V in scale of 60.00V the offest will be 0.04 it will display a value between 9.96V - 10.04V
if we measure a 30V in scale of 60.00V the offest will be 0.04 it will display a value between 29.96V - 30.04V
if we measure a 10V in scale of 100.0V the offest will be 0.4 it will display a value between 9.6V - 10.4V
if we measure a 30V in scale of 100.0V the offest will be 0.4 it will display a value between 29.6V - 30.4V
HKJ:
--- Quote from: 2X on March 18, 2024, 08:51:59 am ---So If theoretically we have a multimeter with specs ±(0%+4) in range of 60.00V & in range of 100.0V:
if we measure a 10V in scale of 60.00V the offest will be 0.04 it will display a value between 9.96V - 10.04V
if we measure a 30V in scale of 60.00V the offest will be 0.04 it will display a value between 29.96V - 30.04V
if we measure a 10V in scale of 100.0V the offest will be 0.4 it will display a value between 9.6V - 10.4V
if we measure a 30V in scale of 100.0V the offest will be 0.4 it will display a value between 29.6V - 30.4V
--- End quote ---
Correct.
A "fun" fact: I have seen a meter where the +number specification was worse than the % specification, even at full scale. I believe that this is sort of misleading. It was a ACV specification where the % was very good, but when adding the +number it was at best average (I do not remember the name of the meter).
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