Measurement Systems Analysis

Question 1

Measurement Systems Analysis (MSA)

Answer 1

• A tool for analyzing for analyzing the variation present in each type of inspection, measurement, and test equipment.
• The system to access the quality of the measurement system
  
  • Allows us to make sure that variation in our measurement is minimal compared to the variation in our process
• Experimental and mathematical method of determining how much variation within the measurement process contributes to over all process variation.

Question 2

Measurement Data

Answer 2

• Collection of methods, tools, or gages and operators used to obtain the measurements.

Question 3

Total Variation Formula

Answer 3

Total Variation = Process Variation + Measurement Variation

Question 4

Why Perform Measurement Systems Analysis?

Answer 4

• The main objection is to gauge the validity of the measuring system and try to minimize the leading to process variation due to the measurement system.
  
  • Gauges the quality of the measurement system or instrument
  • Organizations normally consider measurement data is making decisions regarding the process or business, hence should be accurate
  • Data accuracy is one of the fundamental requirements in DMAIC process. It helps to evaluate the effect of the measurement system on the collected data
    
    • If the measurement system data is inaccurate, we will make the decision based on incorrect data
  • Monitoring and measuring resources is an important requirement in quality management systems such as ISO 9001, AS9100 etc.

Question 5

Fundamentals of Accurate Measurement System

Answer 5

• Measurement System Analysis aims to qualify a measurement system for us by quantifying its accuracy, precision, and stability.
  
  • Measurements are said to be accurate: if their tendency is to center around the actual value of the entity being measured. Attained when the measured value as a little deviation from the actual value.
    
    • Bias
    • Linearity
    • Stability
  • Measurements are precise: if they differ from one another by a small amount
    
    • Repeatability
    • Reproducibility

Question 6

Accuracy

Answer 6

• 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 indication of an inaccurate system

Question 7

Accuracy

Bias

Answer 7

• The difference between observed average measurement to be the true or reference value
• To measure the Bias first needs to measure the same part number of times and then calculate the average of measurement

Simply Bias = Average of measurement value - reference or true value

Question 8

Accuracy

Linearity

Answer 8

• The difference in Bias value over the normal operating range of the measuring instrument.
  
  • In other words, it is the change in Bias over the operating range of the measurement equipment.

Question 9

Accuracy

Stability

Answer 9

• Refers to the capacity of the measurement system to produce the same values over time when measuring the same sample.
  
  • In other words, it is the difference in the average of at least 2 sets of measurements with a gage over time.
• A measurement system is stable if there is no special cause of variation affecting the measurement system bias over time.

Question 10

Precision

Answer 10

• The precision of the measurement system is he degree to which repeated measurement under unchanged conditions show the same result.
  
  • In other words, precision refers to the closeness of two or more measurements to each other

Question 11

Precision

Repeatability

Answer 11

• The variation between successive measurements of the same part, same characteristic, by the same person using the same gage.
  
  • In other words, how much variation do we see in measurements taken by the same person, on the same part, using the same tool?

Question 12

Precision

Reproducibility

Answer 12

• The difference in the average of the measurements made by different people using the same instrument when measuring the identical characteristic on the same part.
  
  • In other words, how much variation do we see in measurements taken by different people on the same part, using the same tool?

Question 13

Measurement Error

Answer 13

• Measurement Error is considered to be the difference between a value measured and the true value.
  
  • It depends upon two things:
    
    • What kind of instrument you are using
    • Who is the person using an instrument
      
      • Therefore, anytime you are using an instrument, keep your mind open about measurement error possibilities

Question 14

How much Measurement Error is Acceptable

Answer 14

• According to AIAG (2002), a general rule of thumb for measurement system acceptability is:
  
  • Under 10% error is satisfactory
  • 10% to 30% error suggests that the system is acceptable. Also, it depends on the importance of the application, cost of the measurement device, cost of repair, and other factors
  • Consider over 30% error is unacceptable and you should improve the measurement system