Electronic gages can help make the benefits of SPC pay big dividends.

The automated collection of dimensional data is an efficient and effective method of getting the most value from statistical process control (SPC) programs.

Electronic gaging is a portal through which this can be accomplished. Today, electronic gages-calipers, dial indicators, micrometers, height gages and other manual measuring instruments equipped with microprocessors and an output port-can help make the benefits of SPC pay big dividends by reducing the costs associated with the production of

out-of-tolerance parts.

This is not to say that traditional, mechanical measuring instruments are not still useful. In terms of accuracy, mechanical and electronic measuring instruments compare favorably, and in the hands of a skilled operator, mechanical instruments provide an essential measurement and inspection capability.

However, because massive amounts of data are needed for SPC applications, electronic gages have advantages over their manual counterparts. One advantage is in reading and recording dimensional data. Manual measuring instruments are subject to operator interpretation when reading the scale, and further errors when data are recorded. Electronic measuring instruments read data automatically when the measurement is taken. Those equipped with a digital output automatically transfer that data to a personal computer or data collector, ensuring accurate recording.

In addition, electronic measuring instruments perform operations that cannot be done efficiently with manual instruments. For example, if an operator needs to measure the center-to-

center distance between two bores using an electronic caliper, he can measure one bore and zero the instrument. Then he can measure the outside-to-outside distance of the bores and automatically get the center-to-center distance. With a manual measuring instrument, the operator has to measure the diameter of one bore, write it down, measure the outside-to-outside distance, write that down, and then subtract the diameter measurement. Each step is subject to operator interpretation and error.

Electronic measuring instruments also offer improved resolution and readouts. Electronic gages with digital outputs speed measurement and data analysis, making the entire operation more efficient by improving inspection throughput.

With these advantages, why would a company not use electronic gages for dimensional data collection?

For a number of years, cost was a factor. Electronic measuring instruments are more expensive than mechanical instruments. However, advances in microprocessor technology have steadily brought the cost of electronic instruments to a level competitive with mechanical instruments. With the improved efficiency possible with electronic measuring instruments, the savings in labor costs can help offset any price difference.

Robustness has been another concern. New electronic measuring instruments are shop-hardened to resist ambient conditions such as airborne contaminants, and are sturdy enough to resist normal bumping and dropping that occurs with use.

One area of concern about electronic gages equipped with a digital output has been the cable that connects the instrument to the data collector, printer or PC. In the past, this cable has been vulnerable because of the wire connectors used at the instrument end. New cable designs do not use a wire connection to the instrument, but use two LEDs instead. This design eliminates wire connector problems such as worn or broken spring clips and corrosion, effectively extending the life of the cable.

Because of improvements in circuit design, the energy consumption of electronic measuring instruments is more efficient than in the past, resulting in improved battery life.

With these concerns accounted for in the new generation of electronic measuring instruments, what lies in the future? Initially, there will be more flexibility in data analysis and reporting.

In the past, a typical data gathering operation for SPC purposes consisted of downloading dimensional data collected with an electronic gage to a special data-collecting device. The data in this device were later downloaded to a central computer where quality control technicians analyzed it, looking for process anomalies. This process information was then sent back to the shop for corrections. While this procedure offered insights into the manufacturing process, it did not provide information on a timely enough basis to provide effective process control.

With the availability of inexpensive desktop computers, however, this same dimensional data can be transferred directly to a computer on or near the workbench. The advantage is that data analysis and the application of the results to the process can be performed close to real time. The improved process control results in less scrap and rework.

Advances in software and firmware have made it easier to connect electronic measuring instruments to computers. In the past, it was necessary to analyze data and prepare reports using special SPC software. Today, while this type of software is still widely used, it also is possible to download data to standard spreadsheet and word processing programs such as Microsoft Excel and Word. These standard software programs are less expensive than proprietary SPC programs and are familiar to most shop personnel.

These improvements make electronic gages a consideration for companies that wish to continue to improve quality through process control.

Pete Schulze is a project manager for Hexagon Metrology's TESA USA division (North Kingstown, RI). For more information, call (800) 283-3600, e-mail [email protected] or visit

www.brownandsharpe.com.