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.

Table 1. Criteria definitions and calculations
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
Engineering Unit conversion calculation
If the tolerance is based on output, then no conversion is required.
EU tolerance based on input

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.

%span calculation based on input
%span calculation based on output

%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.

%URV calculation based on input
%URV calculation based on output

%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.

%Reading calculation based on input
%Reading calculation based on output