R chart

STATISTICAL QUALITY CONTROL

1. Control Charts International Institute Of Population Science Source : Fundamentals Of Applied Statistics By Smruti Mokal & Tejal Lakhan

2. Structure of Control Chart Consist of Three horizontal lines A central line – shows where the process average is centered 2.Upper C ontrol Limit 3.Lower Control Limit Upper control limit (UCL) and Lower control limit (LCL) describes the process spread

3. Variables Variables are those quality characteristic of a product which are measurable and can be expressed in specific units of measurements Eg Diameter of a radio tube which can be measured and expressed in cms

4. R chart In this chart, the sample ranges are plotted in order to control the variability of a variable. used to detect changes in variation within subgroups

5. How to set up R chart We plot the sample range against the sample number Control limit for R chart is given as follows UCL = D4*R CL = R LCL = D3*R D3 and D4 are constants depending on sample size n

6. The x and R chart plots the mean value for the quality characteristic across all units in the sample, plus the range of the quality characteristic across all units in the sample as follows: R = x max - x min .