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Monday, July 28, 2014

Precision vs. Accuracy

It is useful to understand the meaning of the terms “precision and accuracy” when relating to measurement instrumentation. Precision relates to the ability of an instrument to very closely repeat measurements time after time. The term “accuracy” relates to the ability of an instrument to measure values which are very close to the correct value as determined by an industry accepted standard or authority. As can be seen from the image above, instruments can have any of four combinations of precision and accuracy

a) the upper left hand target depicts an instrument which has both low precision (poor reproducibility) and low accuracy (agrees poorly with the correct value); 

b) the lower left hand target depicts an instrument which has excellent repeatability but for which all of its measurements are in error by approximately the same amount; 

c) the upper right hand target depicts an instrument which exhibits poor repeatability, but the average of its measurements is very close to the correct value; and 

d) the lower right hand target depicts an instrument which is very repeatable and for which the average of its readings agrees closely to the correct value.

This clarification of terms is often helpful when communicating with coworkers or customers when discussing data.

Thursday, July 24, 2014

Customer Training at Technidyne

We've had two customers in for training this week at Technidyne.

Crystal and Linda from BASF
BASF has recently purchased a PROFILE/Plus automated testing system with:

* PROFILE/Plus Brightness
* PROFILE/Plus Color
* PROFILE/Plus Roughness & Porosity
* PROFILE/Plus Opacity

To add to their:
* PROFILE/Plus PPS
* PROFILE/Plus Gloss


We perform a lot of customer and agent training at our facility on topics such as:
   * Calibration
   * Operation
   * Standards
   * Measurement Theory (optical, physical, surface, and process testing)
   * Application
   * Service

We are currently adding a new Training Room specifically for these activities. Let us know if we can help you with your training needs.

Monday, July 21, 2014

Gauge R & R Study: The Average and Mean Report (Part 5 of 5)

The average and mean report includes not only the measurements and calculations, but also a graph charting the appraiser results (see below). This chart is useful in pinpointing appraiser training or method issues.

Average and mean charts should not be read as a control chart. The data is plotted by sample number and not time sequence. Each chart plots the mean of each sample part and the range of each sample part by operator. In the example, one can tell that all operators have similar averages on all 10 parts; however, the second operator, Justin Thom, has much more variation on each part. The next step here would be to determine if Justin is following the correct procedures or if he has been properly trained.

Understanding how to properly conduct a gauge R&R study and how to interpret the results is a key skill for quality professionals. For more detailed information, consult AIAG's Measurement Systems Analysis, third edition, 2002, and Evaluating the Measurement Process, Wheeler and Lyday, 1984.

This series of blogs will include:
  • What does it measure?
  • Conducting a Study
  • Evaluating the Gauge Study: The TV Report
  • Evaluating the Gauge Study: The TT Report
REFERENCE: Quality Magazine, Sept. 1, 2009

Thursday, July 17, 2014

Technidyne: 40 Years and Still Going Strong

Technidyne is preparing for its 40th Anniversary in August 2014. Today employees were given 40th Anniversary t-shirts.

Also, announced were the hiring of a new Lab Manager, Nick, a Production Technician, Mike, and a job offer extended to a Service Technician.  Progress continues as Technidyne looks forward to new challenges and opportunities as it completes 40 years of success.

Monday, July 14, 2014

Gauge R & R Study: The TT Report (Part 4 of 5)

The total tolerance (TT) report analyzes the gauge study against the production tolerance of the part that the system is being evaluated to measure. While the categories are the same (EV%, AV%, GR&R% and PV%), the results are percentages of part tolerance. If the system is being evaluated for a particular purpose, then this report gives a true understanding of whether the measurement system is adequate.

If the study is to determine if a measurement system is adequate for a specific purpose, then the results should be evaluated as a percentage of tolerance and the total tolerance report should be used.

This series of blogs will include:
  • What does it measure?
  • Conducting a Study
  • Evaluating the Gauge Study: The TV Report
  • Evaluating the Gauge Study: The Average and Mean Report
REFERENCE: Quality Magazine, Sept. 1, 2009

Monday, July 7, 2014

Gauge R & R Study: The TV Report (Part 3 of 5)

The total variation (TV) report analyzes the gauge study data as a percentage of total variation. The report is divided into sections presenting the equipment variation, appraiser variation, part variation and the gauge R&R.
 
Equipment variation (EV) represents the repeatability of the equipment or measurement device. On the TV chart, it is presented as a percentage of the total variation of the system (see below). The equipment variation percentage is 17.6% of the total variation of the system. While the result in the example is low, a high percentage, greater than 30%, would tell operators that they have issues with the measurement equipment itself that must be resolved. The gauge may need maintenance or perhaps the fixture holding the part for measurement is not adequate.

Appraiser variation (AV) represents the reproducibility of the system. The TV chart also reports the AV as a percentage of the total variation of the system. A high percentage here, greater than 30%, indicates a large operator-to-operator difference. A possible cause could be operators not following proper measurement procedure, not trained properly or perhaps trained in different methods.

Part variation (PV) represents the variation of the products or parts used to conduct the gauge study. In the example, the PV% is 96.4%. One would expect to see a high percentage of the total variation from the parts on an adequate system where the parts truly represent the range of the process variation. If the PV% is low, less than 30%, the parts selected do not represent the full variation of the process.

Gage repeatability and reproducibility (GR&R) represent both the equipment variation and the appraiser variation. The GR&R% returned in the TV report is the percentage of the total variation of the system used by the measurement system. In Figure 1, GR&R% is 26.7%. This means that 26.7% of the total variation is due to the measurement system itself. Rule of thumb for GR&R is that a result of 10% or less means that the system is acceptable. Most of the variation is from the parts and not the measurement system.

If the GR&R is less than 30%, the system may be accepted, but there should be some plan to review the system for improvement. A GR&R result of greater than 30% shows that the system must be improved as the appraisers and equipment contribute to more than 30% of the system variation.
Another critical calculation in determining if the gauge study is valid is the number of distinct categories (NDC). The NDC is the calculation for the number of non-overlapping 97% confidence intervals that span the product variation. In other words, it is basically the part variation divided by the GR&R result and multiplied by a constant. The NDC should be five or greater for the study to be considered valid.

As discussed earlier, a common problem with gauge studies is that the part variation does not represent the expected process variation. If the part variation is too small, then the NDC will be below five and the study should not be considered valid. In this case, operators may sample again to obtain parts that do represent the full range of process variation. Remember to evaluate both part variation and gauge R&R. If the gauge R&R itself is too large, then the NDC will be low as well. If this occurs, operators could have an issue with AV, EV or the measurement system itself.

When evaluating the TV report results, remember that these results are calculated against the process variation only. In the example, the GR&R% is 26.7% of the total variation. This report shows which section of the measurement system may need improvement, but it does not show how the system works within the actual tolerance of the parts. To evaluate the measurement system against the tolerance, one must use the total tolerance report.

This series of blogs will include:
  • What does it measure?
  • Conducting a Study
  • Evaluating the Gauge Study: The TT Report
  • Evaluating the Gauge Study: The Average and Mean Report
REFERENCE: Quality Magazine, Sept. 1, 2009

Wednesday, July 2, 2014

Technidyne Sets Record

Monday, June 30, 2014 was the end of the fiscal year for Technidyne Corporation. It was a record setting year. Technidyne registered its highest revenue year in its 40 year history.





Thanks to all of our employees, vendors, agents and partners for a great year in Fiscal Year 2013-14.  

We are looking forward to an even better year in FY 2014-15. We have many new Technidyne products that will be hitting the market including the Color Touch X.  Also, we continue to see new developments from the companies we represent in North America: ACA Systems, Emtec Electronic, and Techpap.

Again, thanks for the cooperation, hard work and vision that make years like this possible.