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Statistical process control determines whether a process is stable or changing by taking samples of historical data and predicting performance based on pre-set control limits. SPC software can automate that data collection and interpretation to help predict problems before they occur.

Fair enough.

Yet a common challenge with SPC has remained for years. Different machine controllers and software feed data in different file formats, with various headers, trailers, right or left margins, invisible characters and so on. The challenge has been getting all these formats to agree, to make comparing apples to apples possible.

Dynamic Masking

"In general, we still have to deal with a large variety of equipment and communicate in a variety of ways," says Frank Tappen, vice president of solution delivery of SPC-software-vendor DataNet Quality Systems, Southfield, Mich.

Even within the same basic file formats issues still arise, says DataNet President Ned Greenberg. "The layout of that file could be tab or comma delimited, or other organizational methods."

Consider the coordinate measuring machine. To be used with SPC software, different CMM files must be "masked" to ensure SPC reads the correct data-points to, again, compare apples to apples. One common method involves "positional masking," which instructs the software reading the file format to only look at data entered at specific positions and character lengths, such as "4th row, 16th column, 10 characters long." Another method, dubbed "key identifier" masking, instructs software to read only certain words, such as, "Look for the word 'Datum 1X,' and whatever follows is the measurement."