Control - Working with control charts

You've created an Xbar-R control chart to help identify variations in widget weights. 6 observations are selected randomly every day for 7 days Which statements correctly interpret the charts?

A nonrandom pattern is evident Test 1 failed

How do you determine where the control limits should be drawn?

Calculate plus or minus 3 std deviations from the mean

If you are using an Xbar chart to plot variables data, how can you determine where to put the center line?

Calculate the within-subgroup average

Match the elements of an Xbar-s control to the formulas you'd use to calculate them to help determine special cause variation. Each element may match to more than one formula

LCL: - Sbar x B3 - xdoublebar - (a3 x Sbar) UCL: - Xdoublebar + (A3 x Sbar) - Sbar x B4 Center Line: - Sbar

This chart illustrates a data trend known as process drift. Which corrective actions would you take to solve the problem indicated by this control chart?

Make sure that operator fatigue is not a factor Train the operator Repair the machine or use an alternative machine if it's available

Which statements about control charts are true?

Sample size is a key determination in the type of control chart you use Control charts are divided into 6 zones Issues related to materials and machines - for example, too much waste and broken or worn tools - are among the main causes of process variation

Match each step in the control charting process with its associated major activity

Step 1 - Choose the appropriate control chart for your data Step 2 - Plot the data points Step 3 - Connect the data points Step 4 - Determine and draw the center line Step 5 - Determine and draw the UCL and LCL Step 6 - Analyze and interpret the chart

Which data trend does this chart illustrate?

Stratification

You've created an NP chart for a randomly selected sample of 100 washers, to monitor the number of defectives per sample each day for 20 days Which statement correctly analyzes the chart?

Test 1 failed there is special cause variation

Match the corrective actions to the appropriate data trends

Upward or downward shift - Endure your material supply is consistent and make sure operators use the same methods and instructions Recurring cycles - Repair machine or use an alternate machine if it's available, train the operator, and speak with the operator to find out what's causing the problem. Systematic variation - Ensure control limits are set at the correct levels, check testing procedures and determine if inspections should be performed differently or occur more frequently

This chart illustrates a data trend known as stratification. Which corrective actions could solve the problem indicated by this data pattern?

Validate the method employees use to take measurements Ensure employees are following procedures for rational subgrouping Ensure the checking procedure is followed

When should you use a median control chart?

When your process is not perfectly normal When you don't want your control chart limits to be influenced by outliers

You want to determine how many calls in a call center meet duration requirements, so you take eight measurements a piece from each of three shifts. What type of control chart should you use?

Xbar-R

Match Xbar-R and Xbar-s charts with their distinguishing features

Xbar-R charts - Show the difference between the highest and lowest observations within a subgroup Are recommended for subgroup sizes between two and ten Xbar-s charts - Show the std deviation of observations within a subgroup Are recommended for subgroup sizes of more than ten

Match control chart characteristics with the chart types they describe

p chart - Plots the proportion or ratio of defective units per equally sized subgroup u chart - Plots the average number of defects per subgroup np chart - Plots the number of defective units per equally sized subgroup c chart - Plots the number of defects per equally sized subgroup