Tiêu đề 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 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.