ISDS 3115-Chapter 6S "Statistical Process Control"

The quality level of a lot considered good

Acceptable Quality Level (AQL)

A method of measuring random samples of lots or batches of products against predetermined standards

Acceptance Sampling

Variation in a production process that can be traced to specific causes

Assignable Variation

The % defective in an average lot of goods inspected through acceptance sampling

Average Outgoing Quality (AOQ)

The quality level of a lot considered bad

Lot Tolerance % Defective (LTPD)

Variability that affects every production process to some degree and is to be expected; also known as Common Cause

Natural Variations

The theoretical foundation for x-charts, which states that regardless of the distribution of the population of all parts or services, the distribution of x's tends to follow a normal curve as the number of samples increases

Central Limit Theorem

The mistake of a customer's acceptance of a bad lot overlooked through sampling

Consumer's Risk

A graphical presentation of process data over time

Control Chart

A ratio for determining whether a process meets design specifications; a ratio of the specification to the process variation

Cp

A proportion of variation (3o) between the center of the process and the nearest specification limit

Cpk

A graph that describes how well an acceptance plan discriminates between good and bad lots

Operating Characteristic (OC) Curve

The ability to meet design specifications

Process Capability

The mistake of having a producer's good lot rejected through sampling

Producer's Risk

A control chart that tracks the "range" within a sample; it indicates that a gain or loss in uniformity has occurred in dispersion of a production process

R-Chart

A test used to examine the points in a control chart to see if nonrandom variation is present

Run Test

A process used to monitor standards by taking measurements and corrective action as a product or service is being produced

Statistical Process Control (SPC)

Statistically, the probability of rejecting a good lot

Type I Error

Statistically, the probability of accepting a bad lot

Type II Error

A quality control chart for variables that indicates when changes occur in the central tendency of a production process

X-Chart

A quality control chart used to control the number of defects per unit of output

c-Chart

A quality control chart that is used to control attributes

p-Chart