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Fluke accuracy ±(2%+2) - What means the +2?
boggis the cat:
--- Quote from: HKJ on March 18, 2024, 10:29:48 am ---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).
--- End quote ---
That isn't uncommon for the very cheap instruments. Sometimes you will see a change from +/- counts to +/- a value in order to try to be extra squirrelly. Higher priced instruments will occasionally have this crop up in the margins, where they are presenting accuracy data (sometimes only 'typical') for end users that insist on using equipment beyond its real capabilities.
Beware of cut-down specification comparisons that only quote the % values (or other ratio).
Then there is the entire discussion over how realistic some accuracy claims may be. (In general, the bigger name brands even amongst the cheap offerings are a lot more reliable. No-name stuff is a bit of a lottery.)
2X:
--- Quote from: boggis the cat on March 19, 2024, 05:37:18 am ---
--- Quote from: HKJ on March 18, 2024, 10:29:48 am ---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).
--- End quote ---
That isn't uncommon for the very cheap instruments. Sometimes you will see a change from +/- counts to +/- a value in order to try to be extra squirrelly. Higher priced instruments will occasionally have this crop up in the margins, where they are presenting accuracy data (sometimes only 'typical') for end users that insist on using equipment beyond its real capabilities.
Beware of cut-down specification comparisons that only quote the % values (or other ratio).
Then there is the entire discussion over how realistic some accuracy claims may be. (In general, the bigger name brands even amongst the cheap offerings are a lot more reliable. No-name stuff is a bit of a lottery.)
--- End quote ---
With this "a change from +/- counts to +/- a value" you mean that they refer only the measurement scale for instance 0-1.999 0-19.98V, 0-199.7V and the don't refer 2000counts?
boggis the cat:
--- Quote from: 2X on March 19, 2024, 07:13:18 pm ---With this "a change from +/- counts to +/- a value" you mean that they refer only the measurement scale for instance 0-1.999 0-19.98V, 0-199.7V and the don't refer 2000counts?
--- End quote ---
Specifications are generally given in a +/-( [ratio] + [floor] ) form; often with additional notes concerning 'edge conditions' (such as minimum valid reading per range, any over-range capabilities, etc.).
Sometimes a floor given in counts may look bad. For example given a range of 100.000 V, '0.5% + 2000 counts' may look worse than '0.5% + 2 V' at a glance. You may see the % component and not do the mental arithmetic for the 2 V while the 2000 counts stands out (due to being a number of digits).
Ideally a specification should be as clear as possible, but if your product has a poor specification you may be tempted to try to obscure this. (Outright lying is not that common, but don't be surprised if a cheap instrument has an accuracy that sits very close to the maximum calculated specification, whereas an expensive instrument will typically be around 30% to 40% of this or less.)
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