This topic describes how the software calculates the calibration errors.
As Found and As Left Errors (% of Span) Calculation
The following formula is used to calculate the As Found and the As Left errors (% of Span):
Where i = calibration point number
As Found and As Left Errors (% of Reading) Calculation
The following formula is used to calculate the As Found and the As Left errors (% of Reading):
Where i = calibration point number
Error Calculation of Square Root Extraction
Calibration errors for differential pressure flow instruments that require a square root extraction are calculated according to the following formula:
Example:
out.signalmin = 4 mA
out.signalmax = 20 mA
out.signal range = out.signalmax – out.signalmin = 16mA
|
% of Input |
Output Value |
|---|---|
|
0 |
4 + (16 * 0) = 4 |
|
25% |
4 + (16 * 0.5) = 12 |
|
50% |
4 + (16 * 0.707) = 15.3137 |
|
75% |
4 + (16 * 0.866) = 17.8564 |
|
100% |
4 + (16 * 1) = 20 |
Errors are calculated to four decimal places. Any error smaller than 0.0001 will be
displayed as zero (0) and stored in the database as zero.
When not interfacing with the Fluke (using manual data entry), Smart Instrumentation determines the expected output based on linear distribution of the number of points
in terms of input values (that is % of input range). Fluke however, linearizes the
number of points based on the output range. The transfer function is still the same.
When working with square root output calculations, due to the high slope at the range < 1% of input, Fluke linearizes the transfer function between 0 to 1% of input range. The Calibration module has aligned this strategy with Fluke so that same expected results are displayed in Smart Instrumentation.
When setting the source mode to manual, Fluke prompts % of output for the source value for square root calculation. This is standard Fluke behavior. Smart Instrumentation has aligned the task’s parameters for this case when downloading the task to the Fluke calibrator. However, when uploading such results, Smart Instrumentation translates these values back to engineering values using the Ranges fields from the calibration settings. This results in different values being displayed between the Fluke and Smart Instrumentation, however the errors are the same.