Full Scale Tolerance - How to apply full-scale accuracy specification to a gage?

[e006823]

Can someone explain to me how you apply full-scale accuracy specification to a piece of equipment? For example a flow meter, with accuracy specified as +/- 1% full scale, does this mean that when reading at 50% of scale I apply +/- 1% of the full scale tolerance to the results?

Thanks,
Bob

[Jerry Eldred]

If a meter, for example, is 0-100 VDC (most common on analogue meters, due to the source of error being variability of the meter movement/needle), and the spec was +/-1%F.S. , the spec would be +/-1VDC. You would apply that same calculated tolerance anywhere in that range.

If, as in the example, you are checking 10 Volts, the spec is 9 to 11 VDC. If you are checking at 50 VDC, the spec is 49 to 51 VDC, at 100 the spec is 99 to 101 VDC.

There are many ways manufacturers spec tolerances. One is as a portion of full scale, another is as a portion of reading, often you'll see the two combined. Using the same 0-100 VDC meter, if the spec was +/-1%F.S +/-1%RDG, you would add the two together. At 100 VDC, the tolerance would then be 98 to 102 VDC, at 50 VDC the tolerance would be 98.5 to 101.5 VDC, and so on.

Hope this clears things up.

[e006823]

Jerry,

Thanks,

[shard923]

Just to throw a monkey wrench in here. Here is something to think about that we just had to deal with at my cal shop. Pressure Transducers spec'd in %FS BFSL and how to calculate tolerances from that. Along with hysteresis and zero balance.

[Tim Folkerts]

I've seen uncertainties on instruments in terms of

• +/- % of the reading
• +/- % FS (full scale)
• +/- LSD (least significant digit)

But I had to look up "BFSL" = "best fit straight line".


Tim F