Tolerance criteria for calibration calculations
The tolerance criteria in a data sheet determines which algorithm is used to calculate the lower and upper output limits for each tolerance level. Each tolerance criterion represents a specific calculation formula to calculate tolerance limits.
Criterion | Criteria definition | Tolerance calculation based on input | Tolerance calculation based on output |
---|---|---|---|
Engineering Units (EU) |
Tolerances that are based on input are
expressed in input units. The tolerance levels are always expressed
in output units; therefore, a conversion must occur. The conversion
is
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Tolerance |
%Span |
The values for the %Span criterion are calculated from the calibrated input span of the asset. The values are then converted to output units and are added to or subtracted from the desired output value to determine the range limits. The span is the algebraic difference of the input upper and lower range values divided by 100. If the tolerance is based on output, then no conversion is required. |
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%URV |
The %URV criterion is the upper range value divided by 100. If the upper input range value is used, the value must be converted to output units before the tolerance is calculated. The converted tolerance is then added to or subtracted from the desired output value to determine the range limits. If the tolerance is based on output, then no conversion is required. |
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%Reading |
The values for the %Reading criterion are calculated from the nominal input value applied to the asset. The values are then divided by 100, converted to output units, and added to or subtracted from the desired output value to determine the range limits. These values are not constant, but vary with nominal input. If the tolerance is based on output, then no conversion is required. |
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