# GRR Study | Variable MSA Study

## What is a Gauge R&R study in MSA?

→ Gauge R&R study or “Gauge Repeatability and Reproducibility Study (GRR Study)” is a term which is commonly used in Measurement System Analysis.#### → To calculate the GR&R %, following five contributors are to be calculated:

- Equipment Variation (EV)
- Appraiser Variation (AV)
- Gauge Repeatability & Reproducibility (
**GRR**) - Part Variation (PV)
- Total Variation (TV)

### ➤ [1] Equipment Variation (EV) in GRR study in MSA:

→ This is the "within appraiser" variation.
→ Equipment Variation measures the variation of an appraiser when measuring the same part (and the same characteristic) using the same instrument more than one time.

→ Calculation of Equipment Variation:

⇒ Where K1 is a constant that depends on the number of trials.

⇒ For 2 trials, K1 is 0.8862.

⇒ For 3 trials, K1 is 0.5908.

### ➤ [2] Appraiser Variation (AV) in GRR study in MSA:

→ This is the "between appraisers" variation.

→ Appraiser Variation is the variation in the different appraisers when measuring the same characteristic on the same part with the same instrument more than one time.

→ Calculation of Appraiser Variation:

⇒ Where K2 is a constant that depends on the number of appraisers.

⇒ For 2 appraisers, K2 is 0.7071

⇒ For 3 appraisers, K2 is 0.5231

### ➤ [3] Gauge Repeatability & Reproducibility (GRR) in GRR study in MSA:

### ➤ [4] Part Variation (PV) :

→ The part variation is calculated by multiplying the range of the part averages (Rp) by a constant K3.

→ K3 depends on the number of parts.

### ➤ [5] Total Variation (TV) :

## Steps for GR&R Study in MSA with Excel Template:

- Determine the number of parts, the number of appraisers to use and the number of trials
- Select the parts & measuring instrument for the study
- Label the parts from 1 to n and designate the appraisers A, B, etc.
- Conduct the Measurements & Put data into the Excel Template
- Analyzing the Results
- Interpreting the results

###
➤ Step 1: Determine the number of parts, the number of appraisers to use and **the number of trials**

→ The first is the number of appraisers and the number of parts to use.→ The number of parts (n) must be greater than or equal to 5.

→ The number of appraisers (k) must be greater than 2.

→ The number of trials (r) must be greater than or equal to two.

→ This represents how often each appraiser will measure a part.

→ In addition, the n*k should be greater than 15.

→ This gives more confidence in the results.

###
**➤ Step 2: **Select the parts & measuring instrument for the study

→ The next step is selecting the parts to include in the study.→ The parts should be selected to reflect the range of variation in the process.

→ In other words, don't just take 10 parts off the line right in a row.

→ The parts should be selected in the proper method that they cover all possible variants of the manufacturing process.

→ If appropriate, calibrate the gauge or verify that the last calibration date is valid.

### ➤ Step 3: Label the parts from 1 to n & designate appraisers A,B, etc.

###
**➤ Step 4: **Conduct the Measurements & Put data into the Excel Template

→ The parts must be run in random order.→ All appraiser measures the reading each part 3 times.

→ Example trial1 – first in order, trial2 - second in reverse order, trial3 - third random).

→ Start with appraiser A. Appraiser A measures the parts in random order.

→ The results are recorded.

→ This process continues for each appraiser without the appraisers being able to see the results from other appraisers.

→ This cycle is continued until you have completed all trials.

→ Be sure that an appraiser cannot see his/her results from previous trials.

👉

**Click here**

**:**GRR Study Excel Template Download

→ Open the Gauge R&R worksheet to record data.

→ Write data into the Gauge R&R worksheet.

→ Enter the number of operators, trials, samples and specification limits

###
➤ **Step 5: Analyzing the Results**

→ In this study, we have selected three appraisers (A, B, and C) and five parts that represent typical variation in the length output.

→ All appraiser measures the reading each part 3 times.

→ The Calculation is mentioned in the below picture.

👉 Click here: GRR Study Excel Template Download

→ We use the above results to perform the gauge R&R calculations.

→ We start by determining the following:→ The average for each trial for each appraiser

→ Average & Range of each part with each appraiser.

→ The average range for the part

→ These calculations are shown in the table below.

→ Then, calculate the difference between the maximum and minimum of appraiser average.

→ Thus, the difference is

**(3.157) - (2.695) = 0.462**→ The smallest part average is for Part 5 (1.94).

→ So, Rp = (4.10) - (1.94) = 2.16

**→ Putting up these values for all the 5 contributors:**

### ➤ Step 6: Interpreting the results

→ Remember, a gauge R&R study is a study in variation.→ You must have variation in the parts and in the appraisers to calculate the above numbers.

→ We have to check Total Variation to decide that our measurement system is applicable or not?

→ The number that most people focus on first is the %

**GRR**.
→ The following guidelines can be used to determine if the measurement system is acceptable, conditionally acceptable or not acceptable.

**➦ Green: < 10%**

**of TV**

**(**

**Measurement system is acceptable**

**)**

➦

**Yellow: 10-30%**

**of TV**

**(**

**Conditionally acceptable**

**based on the application**

**)**

➦

**Red: > 30%**

**of TV**

**(**

**Measurement system needs improvement**

**)**

→ Sometimes you can look at the %AV and %EV to get insights into where to start improving the measurement system.

→ But the study indicates that the measurement system must be improved.

#### ➦ Also, we will check the number of distinct categories (ndc) in Gauge R&R Study.

→ It is similar to looking at how many possible values there are on a range Control Chart.

→ The calculation is:

ndc = 1.41(PV/

**GRR**) = 1.41(0.872/0.319) = 3.8

→ The integer value of

**ndc should be greater than or equal to 5.**

→ In this case, it is 3.

→ Again, this is an indication that the measurement system needs improvement.

#### ➥ Correction Criteria of Measurement System Analysis:

#### ➥ If Repeatability is large compared to Reproducibility, then the reasons may be:

1. The instrument needs maintenance;

2. Other reason may be the gauge should be redesigned to be more rigid;

3. The clamping or location for gauging needs to be improved;

4. There is excessive part variation.

2. Other reason may be the gauge should be redesigned to be more rigid;

3. The clamping or location for gauging needs to be improved;

4. There is excessive part variation.

#### ➥ If reproducibility is large compared to repeatability, then possible causes may be:

1. The appraiser needs to be better trained in how to use and read the gauge instrument.

2. Calibrations on the gauge dial are not clear

3. A fixture may require to use the gauge in an appripriate manner.

2. Calibrations on the gauge dial are not clear

3. A fixture may require to use the gauge in an appripriate manner.

###
**➤ Some improvement points in Gauge R&R study in MSA**

→ Brainstorm with the team for improvement solutions.→ Determine the best “practical solution” (may require some experimentation).

→ Pilot the best solution

→ Implement the best solution – train employees.

→ Again conduct the study to verify the Improvement.

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