Title 2. CONCEPT OF STATISTICAL QUALITY CONTROL.pdf ✅

PHARMD GURU Page 1 CONCEPT OF STATISTICAL QUALITY CONTROL DEFINITION: Statistical quality control should be viewed as a kit of tools which may influence decisions to the functions of specification, production or inspection. CHARACTERISTICS OF S.Q.C :  Designed to control quality standard of goods produced for marketing.  Exercise by the producers during production to assess the quality of goods.  Carried out with the help of certain statistical tools like Mean Chart, Range Chart, P- Chart, C-Chart etc.  Designed to determine the variations in quality of the goods & limits of tolerance. CAUSES OF VARIATIONS IN QUALITY:  ASSIGNABLE CAUSES: It refers to those changes in the quality of the products which can be assigned or attributed to any particular causes like defective materials, defective labour, etc.  CHANCE CAUSES: These causes take place as per chance or in a random fashion as a result of the cumulative effect of a multiplicity of several minor causes which cannot be identified. These causes are inherent in every type of production. METHODS OF S.Q.C: PROCESS CONTROL:  Under this the quality of the products is controlled while the products are in the process of production.  The process control is secured with the technique of control charts.  Control charts are also used in the field of advertising, packing etc. QUALITY ASSURANCE
PHARMD GURU Page 2  They ensure that whether the products confirm to the specified quality standard or not. CONTROL CHART:  A control chart is a time plot of a statistic, such as a sample mean, range, standard deviation, or proportion, with a center line and tipper and lower control limits.  The limits give the desired range of values for the statistic. When the statistic is outside the bounds, or when its time plot reveals certain patterns, the process may be out of control.  A process is considered in statistical control if it has no assignable causes, only natural variation. PURPOSE & USES OF CONTROL CHARTS: 1. Helps in determining the quality standard of the products. 2. Helps in detecting the chance & assignable variations in the quality standards by setting two control limits. 3. Reveals variations in the quality standards of the products from the desired level. 4. Indicates whether the production process is in control or not. 5. Ensures less inspection cost & time in the process control.
PHARMD GURU Page 3 CONTROL CHATS FOR VARIABLES: 1. V - Chart/ Mean chart: This chart is constructed for controlling the variations in the average quality standard of the products in a production process. 2. R - Chart: This chart is constructed for controlling the variations in the dispersion or variability of the quality standards of the products in a production process. Example: SAMPLE N.O WEIGHTS 1 2 3 4 5 1 15 10 11 14 2 18 10 8 22 3 19 17 10 13 4 12 19 14 20 20 19 26 12 23 Conversion factors for n = 5, A2= 0.577, D3= 0, D4 = 2.115 Types of control charts Control charts for variables V-Chart R-Chart σ-Chart Control cahrts for attributes P-Chart np-Chart C-Chart
PHARMD GURU Page 4 3. σ - Chart: This chart is constructed to get a better picture of the variations in the quality standard in a process than that is obtained from the range chart provided the standard deviation(σ) of the various samples are readily available. Example: Quality control is maintained in a factory with the help of standard deviation chart. Ten items are chosen in every sample. 18 samples in all were chosen whose ΣS was 8.28. Determine the three sigma limits of σ- chart. You may use the following: n = 10, B3 = 0.28, B4 = 1.72, K =18. Solution: = S/K= 8.28/18= 0.46 UCL =B4.L =1.72x0.46 = 0.7912 LCL =B3.L =0.28x0.46 = 0.1288 CONTROL CHARTS FOR ATTRIBUTES: 1. P-chart: This chart is constructed for controlling the quality standard in the average fraction defective of the products in a process when the observed sample items are classified into defectives & non-defectives.