Measurements are the basis for all process improvement. We measure activity, process variables, productivity, yield, and the characteristics of the resulting product. Any activity that will contribute to the bottom line, any continuous improvement project, all require that we measure, analyze, evaluate, and refine. Most often, we take these measurements for granted and concentrate on the bigger picture—the activities that follow.
Still, there are basic measurements underlying all of our decisions and improvement activities. From basic numbers such as inventory counts, number of good and defective units or batches, and time, we derive measures; yield, good product per labor hour, even bottom-line business results such as Return on Net Assets (RONA).
Measurement consulting from P.G. Stein, in conjunction with The Automated Technology Institute, covers both basic scientific, laboratory, or manufacturing measurements, and the development and validation of technical and business surrogates to directly drive manufacturing and business decisions. Here are some examples where our specialized expertise and consulting in measurements can improve your processes, your information, and ultimately your bottom line.
Consulting on Basic Measurement Principles and Practices
Necessary accuracy and precision
ISO 9001-1994 and the other ISO 9000 standards state: "The supplier shall determine the measurements to be made and the accuracy required, and select the appropriate inspection, measuring, and test equipment that is capable of the necessary accuracy and precision".
Whether or not your enterprise is registered to one of the ISO Standards, this requirement is central to all measurement activity. We offer a complete service, from determining one individual measurement through a total system analysis. The most important aspect of this service is that we determine the accuracy and precision required by each measurement in your manufacturing process—and then recommend a complete measurement system to deliver the required capability. This recommendation may simply indicate better ways to use existing equipment, or may include new hardware, software, fixturing, data analysis, measurement protocols, sample collection and preparation… whatever is needed.
Recently, for example, we studied the weighing and color-matching processes for a maker of colorant additives. We determined that they didn't have the information needed to definitively determine the accuracy and precision needed, and we proposed methods for how to get this information, after which they will be able to calculate their required measurement capability. This work is still in process.
Knowing the measurement uncertainty
The ISO 9000 standards also state: "Inspection, measuring, and test equipment shall be used in a manner which ensures that the measurement uncertainty is known and is consistent with the required measurement capability". Remember that the measurement process (the manner in which the equipment is used) is more than just the test instrumentation—it's the whole end-to-end facility including fixturing, sample preparation, operator variability, etc.
In the last couple of years, measurement uncertainty has become a central topic of interest among industrial users of metrology. The ISO requirements quoted above, plus new requirements from the Automotive industry's QS-9000 standards, plus the ISO Guide 25 for Calibration Laboratories and the US Standard Z-540-1 all have an understanding and quantification of uncertainty as their central focus—and most practitioners don't know how to do that in a way that conforms to these standards.
Our consultants can show you how to meet these standards, how to calculate measurement uncertainty according to the ISO Guide, and how to set up your measurement systems so that monitoring and reporting of uncertainty is part of your day-to-day activity. Even better, following these protocols leads to a stable, well-understood, and ultimately less expensive measurement system. Many of the details may be found in our discussion of measurement assurance, below.
In-house metrology and calibration versus outsourcing
Every measurement activity must conduct some local measurements and must send others out to calibration suppliers. Even NIST refers to the International Bureau in Paris or conducts round-robin tests with other National and Primary labs. Where and why to make this tradeoff is different for each situation, and the expertise for this decision is rarely available within any enterprise.
We recently conducted an outsourcing study for a Fortune-100 industrial manufacturing company. They have a first-rate metrology department and were comfortable with its continuing operation, but an upcoming facility move was forcing the department to relocate, and the cost of moving or rebuilding the laboratories was large, bringing the need to consider alternatives into focus. We visited the lab, evaluated the need for an internal metrology department from the perspective of a disinterested outside party, and provided a written report, including a recommendation that was accepted.
Calibration and Documentation
Once again, ISO standards indicate a necessary activity: "The supplier shall establish and maintain documented procedures to control, calibrate, and maintain inspection, measuring, and test equipment (including test software) used by the supplier to demonstrate the conformance of product to the specified requirements." Our measurement consulting activities can establish, assess, validate, and improve all of your conventional or unusual measurement systems, documentation, history, practices (including calibration frequency and accuracy). We can review basic measurement activities to find excessive calibration, unnecessary tampering with the metrology system, measurements carried out with needlessly high accuracy (and its accompanying high costs), and inappropriate or duplicated record-keeping. We are conversant with modern software for measurements documentation and for calculation of the tradeoffs between calibration frequency and risk.
For example, we recently advised a firm that was calibrating its floor gages monthly that there was almost no risk in calibrating most of them yearly! This saving has enabled them to concentrate the efforts of their measurement staff on adding tools to the gage system that had never been calibrated.
Consulting on Advanced Measurement Principles and Practices
Measurement assurance is a modern approach to maintenance and operation of a measurement system. It operates well in both industrial and laboratory settings, and enhances measurement quality while reducing calibration load and costs. The concepts of measurement assurance are analogous to those of quality assurance.
By viewing measurement as a process, measurement assurance makes creative use of familiar process monitoring, control, and improvement tools from quality, such as control charts and capability studies. Measurement assurance controls the whole measurement system, not just the calibration of the measuring instrument. This makes conformance to the ISO requirements discussed above easy, reduces calibration load and costs, and greatly increases confidence in the measurements made.
Typically, individual items of normal product are designated as check standards. These units are measured periodically (and not expected to change in value when measured) and the results control charted. Any variation (and there will be variation) in those results is due to the measurement system, not the unit under test. The charts will show if the variation experienced is normal or abnormal. If abnormal, the measurement system has failed and can be repaired and put back in order. If the variation is normal, its magnitude can be reported as one major component of the overall uncertainty. This eliminates much of the ISO effort required to determine and report total uncertainty.
Measurement capability studies and finding sources of uncertainty
Once the requirement for accuracy and precision has been determined, and the actual accuracy and precision of the system measured, it often happens that it's not good enough. If the requirements of measurement quality cannot be relaxed, the measurement system must be improved.
The first improvement step is to determine which part of the system is contributing the greatest uncertainty. To do this, we conduct measurement capability studies. These are statistically designed experiments that quantify the error contributions of each part of the system. Once this determination has been made, the measurement capability may be improved by reengineering or replacing the offending equipment or process.
For example, we found a blending process in which over 95% of the total variation in the measurement of the results was due to the way the measuring sample was prepared, and not to errors in the instrumentation that were suspected by the client. A new preparation method was designed that solved the problem without buying or repairing any equipment at all.
Traceability refers to the ability to trace the result of a measurement or calibration to National standards through an unbroken chain of comparisons, each with stated uncertainties. It's another ISO requirement that is often left to an outsourced supplier. Sometimes, though, this can't be done.
In one lens factory where we consulted, a beautiful, expensive master standard of curvature was probably correct but the maker of that standard would not certify traceability, leaving the entire process unsure and not conformant. We designed a simple, easily traceable new way to calibrate the lens curvature instruments that cost almost nothing, and the previous master standard was placed in the company museum.
Sophisticated review of measurement practices
Measurement is a very common practice. Every industrial, engineering, and scientific endeavor makes measurements as a routine part of their activities. Sometimes, though, the very ubiquity of measurements makes people take them for granted. It's often easy to make routine measurements, and that adds to the opportunity to miss some of the more sophisticated aspects of measurement practice. When these advanced opportunities are taken into account, large savings, or vastly better products, or both can result.
Recently, we were working with a major manufacturer of large, curved glass panels. The dimensional requirements for the curvature were tight, and final yield due to curvature rejects were high. Our investigations found that the shape of the panel is measured at 89 discrete points, and product failure is declared if the location of any one of the 89 is out of specifications.
Our analysis of this approach noted that the 89 test points were highly correlated. This is not remarkable: since the surface of the panel is smooth, adjacent points are likely to be close to each other in position error. Nevertheless, since they are correlated, the practice of rejecting the panel for any single failure is unnecessarily harsh and resulted in an artificially high reject rate. Many high quality, completely useable panels were being scrapped.
We replaced the one-of-89 rule with a sophisticated two-dimensional curve fit on the 89 points, plus an algorithm to calculate the overall deviation of the actual panel curvature from the curvature specified by the design equations. Accept-reject decisions were then made according to this overall deviation. Now, measurement correlation is not a factor in determining the reject rate of this manufacturing process, and the panels that are accepted are more likely to satisfy the customer's purpose and requirements.
Education and Training on Measurement, Uncertainty, Calibration, and Measurement Systems
Perhaps the greatest single problem facing metrology today is a lack of educational opportunities. Only three or four two-year college programs exist, and the military, which used to train large numbers of cal technicians and engineers, has completely abandoned doing so. It's not difficult to find a wide variety of courses in ISO 9000 auditing, quality management, or modern quality tools, but metrology training is almost nonexistent.
P.G. Stein Consultants, in conjunction with ATA Institute and Measurement Associates, Inc., offers a wide range of in-house and public seminars and courses, ranging from the most basic training in calibration principles and practices up to the most sophisticated educational offerings in this field available anywhere.
Please discuss your education and training needs in this area with us. We will be able to customize a program that precisely meets your needs.