Variation in Measurement System | Various Types & Examples

What is the Variation in Measurement System?

→ It is sometimes described as spread or dispersion to distinguish it from systematic trends or differences.
→ Measures of variation are either properties of a probability distribution or sample estimates of them.
→ The range of a sample is the difference between the largest and smallest value.
→ The observed variation in process output is not simply due to the process itself, but it is due to the process and gauge that results in an inadequate Measurement System.
→ It is mentioned in the below picture.

Measurement System Variation



Classification of Variation in Measurement System:

→ The classification is mentioned in the below picture.

Classification of Variation in Measurement System

[1] The actual process variation is due to the below parameter in the system
      ⇢ e.g. Cycle time
      ⇢ Dimension data
      ⇢ Number of defects
      ⇢ Some other factor


[2] The measurement system variation further divided into two parts
      ⇢ (A) Precision (related to variability): It is the closeness between the measured value, how close all value to each other
      ⇢ (B) Accuracy (related to a central location): It is the closeness between the true value and measured value.
Read about Precision and Accuracy with examples
      ⇢ (A) Precision is divided into 3 parts
                (a) Resolution: It is the ability of the instrument with an operator to detect small changes in the characteristic of the object.
                (b) Repeatability: It is due to the error in gauge
                (c) Reproducibility: It is due to the operator's error or we can say that appraiser's error
Read about Repeatability and Reproducibility
 with examples
      ⇢ (B) Accuracy is divided into 3 parts
                (a) Linearity: It is the bias with respect to length
                (b) Bias: It is the difference between the average measured value with true value.
                (c) Stability: It is the bias with respect to time.
Read about Bias, Linearity, and Stability with examples

Causes of Measurement Variation:

 → The purpose of the system is to validate before they are considered as true data and used as a basis for decision making.
 → Refer to some of the below important causes.

[1] People:
→ People are the most important factor in this.
→ Due to the repetitive activity of measurement, it becomes a monotonous task and sometimes errors are made.
→ Also, sometimes employees intentionally avoid work due to some other reason and manipulate the readings.

[2] Equipment/Instrument:
→ Faulty equipment or instrument is another major factor that results in getting inaccurate readings.
→ The equipment or instrument is not calibrated then we can not rely on that. It is not recommended. → Due to continuous use instruments wear out.
→ Regular maintenance and calibration of the instrument are essential.

[3] Complex Calculation:
→ Sometimes, due to complex calculations, the possibility of error is due to a lack of proper communication or selection of proper data set.

[4] Lack of Standard Operating Procedures (SOP):
→ It is important that the standard operating procedure should be available for any operation or measurement.
→ Also, it should be communicated to every person that needs to know it.

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