Accuracy Files, whether pre-defined for Instrument FSCs or are developed by the user for specific applications, are vital to the proper calculation of uncertainties in your procedures. This article will clarify some of the nuances of using Accuracy Files and the MET/CAL Configuration Settings that alter how they are read.
At the beginning of a procedure, the MET/CAL Runtime will scan the accuracy file directory for the required files based on the instrument FSCs and specific accuracy files referenced throughout the procedure.
Accuracy Files contain a header which describes the characteristics of the file.
The header is surrounded by the "Begin Header" and "End Header" tags, meaning all header information must be contained within these tags to be used properly by MET/CAL.
The instrument parameter is connected to the system device name and must match exactly. "Fluke 5730" in the instrument parameter will not work, however the system name of "Fluke 5730A" will work correctly.
The interval can be entered in any standard unit of measurement format used in MET/BASE or MET/TEAM. A range of intervals can also be used. The format for a range of intervals is two values in the same unit of measure, separated by a dash, followed by the unit of measure, as in "180-365 Days" or "3-12 Months."
A few of the configuration parameters in MET/CAL alter the way the interval field is read by MET/CAL. The first is the "Accuracy Check" checkbox on the Metrology tab.
- When this option is enabled, MET/CAL checks the configured standard associated with the FSC used to ensure that the accuracy file interval matches the calibration interval in the database.
- When this option is disabled, MET/CAL uses the accuracy file based on the FSC used, specifically the file named "<FSC>.acc". All other accuracy files are ignored and no interval check is performed.
The next parameter that affects this process is the "Accuracy File Interval Conflict". The options for this parameter are:
- Error. This is the default behavior. When the interval in the accuracy file does not match the database, an error is reported in MET/CAL Runtime.
- Shortest. MET/CAL uses the shortest interval available among accuracy files for the given FSC. If the acc folder contains files for a 90-day, 6-month, and 1-year interval of the 5730A, the 90-day file will be used when Shortest is selected.
- Longest. MET/CAL uses the longest interval available among accuracy files for the given FSC. If the acc folder contains files for a 90-day, 6-month, and 1-year interval of the 5730A, the 1-year file will be used when Longest is selected.
In the Metrology (Continued) tab of the Configuration screen, two additional settings deal with the interval comparison. The first is the "Database to Accuracy File Interval Match". This setting determines how close the accuracy file interval needs to be to the database interval. This is intended to allow matching of things like 12 Months to 1 Year or 365 Days.
A second parameter, "Database to Accuracy File Interval Range Match", performs the same functionality for ranges of intervals. A 3-12 Month accuracy file combined with a 50% range match setting would accept database calibration intervals between 1.5 and 18 months.
The final required portion of the accuracy file header is the confidence level, expressed in the number of standard deviations or sigma. The word "sigma" is not required in the header. This value is used during the calculation of measurement uncertainty.
One additional option parameter in the accuracy file header is "asset." When an asset number is identified, the accuracy file applies only to that specific asset.