# Statistical Quality Control SQC and Statistical Process Control SPC. Details.

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### Which Version to Buy: Premium or Basic?

SQC for Excel™  is a Microsoft® Excel add-in program for developing statistical Quality Control (SQC) and Statistical Process Control (SPC) calculations, reports and charts automatically.

The main difference between the basic and Premium version of SQC for Excel™ is more functionality, lets go over them one by one.

Please read the following page and fill this table. If you have answered Yes any of the below questions, please order the Premium SQC for Excel™ version.

 Functionality Yes / No 1 Partial Component Analysis (PCA). [____] 2 Nested SQC Charts [____] 3 Online [____] 4 Changing and Saving Charts format [____]

### Partial Component Analysis (PCA ).

Statistical process control, SPC, is being implemented across the industry without consideration to the multivariable nature of the measurements.

The statistical process control, SPC, and statistical quality control, SQC, foundations are based upon the detection of a statistically significant change in a given process. When a process can be described by a single measurement, such as making an object with a desired length, implementation of these techniques becomes an easy task.

However in the majority of the industries, a given process such as a reactor can not be described completely by a single measurement. Implementation of SQC and SPC technology will yield hundreds of control charts, which will identify some causes, but not the status of the process.

The multivariable nature of processes makes it difficult to provide the unit operator with the information with respect to the health of the process based on SQC and SPC technology due to the number of charts generated.

The PCA technique implemented in the Premium SQC for Excel™ reduce a large multivariable system (i.e. 10 tags with 200 measurements) to a manageable system (i.e. 2 tags with 200 measurement) while preserving most of the information in the original system. Suppose that you have system with 5 measurements as it is shown in the figure below.

Application of normal SQC charts will yield to out of control charts. However, with 3 simple clicks.

1. Select the data from the 40th to 140th measurement and Start SQC for Excel™
2. Click OK for the data type
3. Click OK for the data headers
1. Select PCA as the output.
2. Check the charts ( PCA chart is condensed chart of all variables plotted as normalized and is plotted as +- 3 which means +- 3 Sigma).

The SQC chart is in control.

Then select all data (40th to 200th ) and re-do the PCA. Observe that the ***

Look at the SQC PCA chart, it takes off after 141 sample, and checking the data shows the first line is draping rapidly.

If you add this functionality to you alarm systems, you can detect run away measurements very easily.

The question is:  do you have multi-variable data?  If so you should purchase Premium SQC for Excel™.

### Nested SQC Charts

Suppose a process generates 15 batches of a product. For each batch, 2 samples are taken and the thickness of each sample is measured 2 times.

Using the standard SQC charting techniques described in the previous sections, we can analyze the process using X-Bar and S Charts:

Analyzing the above data yields the following X Bar and S charts:

Question:  is your process out of control? With the above technique, you can not be certain.

Considering the above charts, the X-Bar chart is severely out-of-control. In interpreting these charts, one should realize that the control limits in the X-Bar chart were calculated on the basis of the standard deviations within the subgroup on the basis of the within-sample variability. The subsequent subgroups, however, are not only subject to within-sample variability, but also to between sample to sample and batch to batch variability.

What are the sources of variation in a product response? There are three major sources of variation in a process:

1. Measurement variability

2. Sampling variability (within batch)

3. Batch to batch variability

Each of the three sources of variability adds variation or error to the results. The sample pulled from the batch and tested yields to:

E = X - Xbar (Average)

Where:

E is the error,

X is the measurement and

Xbar (Average) is the population average.

The overall error has three components corresponding to three sources of variations:

E = E Batch + E Sample + E Measurement

Where:

E Batch is the error caused by batch to batch variability,

E Sample is the error caused by batch to sampling variability and

E Measurement is the error caused by batch to measurement variability.

By definition, these errors have zero averages and can be assumed to be represented as normal distributions with fixed variances.

The standard deviation, s , calculated from the data represents an estimate of the combination of these error components.

s 2= s Batch 2 + s Sample 2 + s Measurement2

Where:

s 2 is the total estimated variable

s Batch 2 is the batch-to-batch estimated variance

s Sample 2 is the sample estimated variance

s Measurement 2 is the measurement variance

This is lots of statistics, however, the SQC for Excel™ Premium version makes this very easy to handle.

However, you need to run SQC for Excel™ Premium version and you get the following chart:

Now you can say you are in control. If you have multiple sources of data you should consider Premium SQC for Excel™.

### Online SQC for Excel™

The Premium SQC for Excel™ updates all worksheets selected in the Analysis dialog. To ensure that the Premium SQC for Excel™    program does all calculations on time, please follow these steps:

• From the SQC menu, choose the Analysis option.
• Change the parameters to get the following setup:
• Click on the NEXT button.
• Select the worksheet TAB labeled "Online".
• Set the following Parameters

 Variable Description Value Start and Stop Button These buttons Start and stop Premium SQC for Excel™. Do not use now. Trigger External:  The content of the cell B3 is changed externally. Internal:  The program works at frequency entered in cell B4. Select Internal trigger and enter 00:01:00 for 1 minute in cell B4. Data The data to be used by Premium SQC for Excel™. Enter =Now() in cell B8. Output The data to be sent to the External source. Enter the UCL and LCL from the calculation worksheet. B13 à =Calculation!C12B14 à =Calculation!C11 Reports and Saving This option allows the user to print a report and save the data to a disk. Select both options.
• Save the Spreadsheet as ONLINE.XLS

### Setting the external data generator

Do the following steps to Start the SQC_DDE:

• Double click on SFX_DDE.EXE file in the SQC folder
• Set the parameters as shown above
• Check mark the Start Sending data
• Check that the values in Data row in the ONLINE.XLS file is changing.

### Starting the Online SQC for Excel™

Once the external data is being forwarded to the Online.XLS, you can Start the Premium SQC for Excel™ program with the following steps:

• From SQC menu, choose Report and set it as shown below.

In the Online worksheet click on the Start button.

Note: You need to click the STOP button to stop the online program. In case of emergency press the ESCAPE key and then click on the END button. The ESCAPE key will make the program terminate incorrectly and you will need to Start over again.

### Checking the results

SQC for Excel™ automatically updates all relevant calculations and charts in the online spreadsheet.

### SPC/SQC for Excel Start

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### See Also: Charting Software & Statistical and Quality Control or, All Software

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