Measurement Systems Analysis MSA is a tool for analyzing the variation present in each type of inspection, measurement, and test equipment. It is the system to assess the quality of the measurement system. In other words, it allows us to make sure that the variation in our measurement is minimal compared to the variation in our process.
Measurement is key and essential in six sigma. Measurement System Analysis MSA is an experimental and mathematical method of determining how much the variation within the measurement process contributes to overall process variability. Measurement data is a collection of methods, tools, or gages and operators used to obtain the measurements.
Remember that DMAIC is a tool for removing defects from our process — especially by limiting variation. Moreover, that total observed variation comes in 2 flavors:. If you are measuring using a measuring cup that is not very accurate and your colleague uses an accurate device, you will have different measures. The accumulated variation between your two measuring cups is Measurement Variation. And the phone associates are graded on that quality, which impacts their paycheck.
The main objective of Measurement system analysis is to gauge the validity of the measuring system and try to minimize the leading to process variation due to the measurement system. Measurement System Analysis aims to qualify a measurement system for use by quantifying its accuracy, precision, and stability. Measurement accuracy is attained when the measured value has a little deviation from the actual value.
Accuracy is the difference between the true average and the observed average. If the average value differs from the true average, then the system is not accurate. This is an indication of an inaccurate system. The precision of the measurement system is the degree to which repeated measurement under unchanged conditions show the same result. Straydog Include Straydog in your post and this person will be notified via email. March 7, at am About the measurement system analysis, how can i do it?
Because there is no gage, no operator! Thanks a lot 0. The diagram below illustrates the difference between the terms "Accuracy" and "Precision": Efforts to improve measurement system quality are aimed at improving both accuracy and precision. Requirements Following are general requirements of all capable measurement systems: Statistical stability over time. Variability small compared to the process variability. Variability small compared to the specification limits tolerance.
The resolution, or discrimination of the measurement device must be small relative to the smaller of either the specification tolerance or the process spread variation. If the resolution is not fine enough, process variability will not be recognized by the measurement system, thus blunting its effectiveness. Measurement Systems Analysis Fundamentals Determine the number of appraisers, number of sample parts, and the number of repeat readings.
Larger numbers of parts and repeat readings give results with a higher confidence level, but the numbers should be balanced against the time, cost, and disruption involved. Use appraisers who normally perform the measurement and who are familiar with the equipment and procedures.
Make sure there is a set, documented measurement procedure that is followed by all appraisers. Select the sample parts to represent the entire process spread. This is a critical point. If the process spread is not fully represented, the degree of measurement error may be overstated. If applicable, mark the exact measurement location on each part to minimize the impact of within-part variation e.
Parts should be numbered, and the measurements should be taken in random order so that the appraisers do not know the number assigned to each part or any previous measurement value for that part.
A third party should record the measurements, the appraiser, the trial number, and the number for each part on a table. Stability Assessment Select a part from the middle of the process spread and determine its reference value relative to a traceable standard. If a traceable standard is not available, measure the part ten times in a controlled environment and average the values to determine the Reference Value. Keep the number of repeats fixed.
Take readings throughout the period to capture the natural environmental variation. If there are errors in our measurement system we will be making decisions based on incorrect data. We could be making incorrect decisions or producing non-conforming parts. A properly planned and executed Measurement System Analysis MSA can help build a strong foundation for any data based decision making process. MSA is defined as an experimental and mathematical method of determining the amount of variation that exists within a measurement process.
Variation in the measurement process can directly contribute to our overall process variability. Before we dive further into MSA, we should review the definition of a measurement system and some of the common sources of variation. A measurement system has been described as a system of related measures that enables the quantification of particular characteristics.
It can also include a collection of gages, fixtures, software and personnel required to validate a particular unit of measure or make an assessment of the feature or characteristic being measured. The sources of variation in a measurement process can include the following:. All of these possible sources of variation should be considered during Measurement System Analysis. Evaluation of a measurement system should include the use of specific quality tools to identify the most likely source of variation.
Most MSA activities examine two primary sources of variation, the parts and the measurement of those parts. The sum of these two values represents the total variation in a measurement system.
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