CHECK SHEET &

CONTROL CHART

BY :

N I T E S H KU M A R T I WA R I

M B A ,

The seven major tools are

1) Histogram2) Pareto Chart4) Cause and Effect Diagram5) Defect Concentration Diagram6) Control Chart

7) Scatter Diagram 8) Check Sheet

Control Chart

Check Sheet

What is Check Sheet?

• A check sheet is one of the seven basic quality tools. Data collection can often become an unstructured and messy exercise. It is a simple form you can use to collect data in an organized manner and easily convert it into readily useful information.

• The function of a check sheet is to present information in an efficient, graphical format.

• Main applications of a check sheet include registering how often different problems occur and registering the frequency of incidents that are believed to cause problems.

A check sheet is used to:

• Clearly identify what is being observed. The events being observed should be clearly labeled. Everyone has to be looking for the same thing. • Keep the data collection process as easy as possible. Collecting data should no become a job in and of itself. Simple check marks are the easiest. • Group the data. Collected data should be grouped in a way that makes the data valuable and reliable. Similar problems must be in similar groups. • Be creative. Try to create a format that will give you the most information with the least amount of effort.

How to construct a check sheet:

• Clearly define what events (problem or process) are to be recorded. (Add a category of other to capture incidents not easily categorized into any of the specified groups. • Define the period for data recording and suitable

intervals. The time period should be representative (that is, a one day sample on Monday may not be representative of a typical day). • Design the check sheet to be used during data recording, allocating space for recording, and for summarizing within the intervals and the entire recording period. • Develop a check sheet that is easy to understand. All columns should be clearly labeled.

• Plot the information on a check sheet.

• Perform the data collection during the agreed period, ensuring that everyone understands the tasks and the events to be recorded.

• Analyze the data to identify events with unusually high or low occurrences.

• Train all those involved on gathering data. A uniform data collection technique is vital.

Advantages of using a check sheet:• Effective way of displaying data• Easy to use• Can identify the root cause of a problem• A first step in the construction of other graphical tools• Provides a structure for uniform data collection• Can be used to substantiate or refute allegations

An example of the use of a check sheet

A book store located in a large shopping mall consistently achieved lower sales per day than budgeted. The staff noted that quite a few customers came into the store to browse, but left without buying anything. When considering this problem (not tapping the customer base potential there), a wide range of possible causes surfaced including: • The customers did not find what they were looking for. • The staff did not offer the necessary help. • Sought items were temporarily sold out. • Sought items were not carried by the store. • Prices were too high. • There was too long a line at the checkout counter. • Certain types of credit cards were not accepted. • Lighting was poor in some areas of the store. • There were no places to sit and look through books before deciding to buy.

Control Chart

What is a Control Chart?

“A statistical tool used to distinguish between process variation resulting from common causes and variation resulting from special causes.”

• Statistical process control is a collection of tools that when used together can result in process stability and variance reduction.

A process that is operating with only chance causes of variation present is said to be in statistical control.

A process that is operating in the presence of assignable causes is said to be out of control.

The eventual goal of SPC is the elimination of variability in the process.

Basic Principles

A typical control chart has control limits set at values such that if the process is in control, nearly all points will lie within the upper control limit (UCL) and the lower control limit (LCL).

GRAPH

Inputs Out put

Control Chart

Process

Verify

and

follow up

Detect

Assignable cause

Identify ro

ot cause

of the p

roblem

Implement

corrective action

Process Improvement through Control Chart

Important uses of the control chart1. Most processes do not operate in a state of

statistical control2. Consequently, the routine and attentive use

of control charts will identify assignable causes. If these causes can be eliminated from the process, variability will be reduced and the process will be improved

3. The control chart only detects assignable causes. Management, operator, and engineering action will be necessary to eliminate the assignable causes.

Popularity of control charts

1) Control charts are a proven technique for improving productivity.

2) Control charts are effective in defect prevention.

3) Control charts prevent unnecessary process adjustment.

4) Control charts provide diagnostic information.

5) Control charts provide information about process capability.

Types the control chart• Variables Control Charts

– These charts are applied to data that follow a continuous distribution.

• Attributes Control Charts– These charts are applied to data

that follow a discrete distribution.

Design of a Control Chart

Suppose we have a process that we assume the true process mean is = 74 and the process standard deviation is = 0.01. Samples of size 5 are taken giving a standard deviation of the sample average, is

0045.05

01.0

nx

Design of a Control Chart

• Control limits can be set at 3 standard deviations from the mean in both directions.

• “3-Sigma Control Limits” UCL = 74 + 3(0.0045) = 74.0135 CL= 74 LCL = 74 - 3(0.0045) = 73.9865

Design of a Control Chart

Choosing the type of control chart

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