ACCEPTANCE SAMPLING PRESENTED BY SREEDEVI K.N M.Sc INDUSTRIAL FISHERIES III SEMESTER
INTRODUCTION Quality control is an activity in which measures are taken to control quality of future output. Sampling refers to observation of a population or lot for the purpose of obtaining some information about it. Acceptance sampling is a quality control technique.
DEFINITION Acceptance sampling is defined as sampling inspection in which decisions are made to accept or reject products or services. It is a decision making tool by which a conclusion is reached regarding the acceptability of lot.
ADVANTAGES Acceptance sampling eliminates or rectifies poor lots & improve overall quality of product. Reduces inspection costs & risk. In inspection of sample greater care will be taken so that results may be more accurate. A rejected lot is frequently a signal to the manufacturer that the process should be improved. It provides a no of alternative plans in which a single sample is taken, two or indefinite no of samples may be taken from a single lot.
ATTRIBUTES SAMPLING PLAN Attributes sampling is most commonly used, more than 1 type of quality characteristics can be considered for each sample. Measurements are simpler to make. It requires a larger sample size than variables sampling plan.
SINGLE SAMPLING A plan in which inspector is forced to make a decision concerning acceptability of a lot or batch on the basis of inspection of units in one sample taken from that lot. It can be described in terms of 3 constants. N,the lot size n,the sample size c,the acceptance number c is the maximum allowable defects in sample If sample contains c or fewer defectives, lot will be accepted & if it contains more than c lot will be rejected.
DOUBLE SAMPLING These are characterized by two sample size along with two sets of acceptance rejection numbers. The two sample sizes may or may not be equal. It can be described in terms of c1,c2,n1,n2 MULTIPLE SAMPLING• In this 3 or more samples might be taken before a decision is reached regarding the acceptability of a lot.• It results in smaller average sample size.
SEQUENTIAL SAMPLING An extreme case of multiple sampling in which sampling might continues until the lot is exhausted. It calls for inspection on an item by item basis. Decision is made after each item is inspected concerning whether lot should be accepted or rejected or sampling continued. Sampling & decision making continues until a clear cut decision is obtained either to accept or reject.
VARIABLE SAMPLING Variables plan need measurement type data & decision must be based only on one such measurement characteristics. It is efficient because variables carry more information than attributes. Based on mean & standard deviation characteristics. They are difficult to use.
OPERATING CHARACTERISTIC CURVE (oc) A curve which serves to describe an acceptance plan in terms of probability of accepting lots of various quality levels with the plan. Pa =probability of accepting a lot P` =actual proportion of defectives pa p`
SAMPLING RISKS Both producer & consumer will agree on two proportions to represent the acceptable proportion of defectives in the lot. AQL(accaptable quality level) : it represents the maxi proportion of defectives acceptable by consumer. LTPD(lot tolerance percent defective): it represents the mini proportion of defectives which consumer finds unacceptable.
AVERAGE OUTGOING QUALITY AOQ is the average quality in terms of fraction or % defectives for inspection operations. These are done under 2 conditions such as rejected lots be screened &all defectives that contain be replaced by good articles, lot sizes of product be constant. The maxi value of AOQ is average outgoing quality limit(AOQL). Each acceptance sampling plan can be described in terms of AOQL it will generate.
ACCEPTANCE SAMPLING SYSTEMS American national standard, sampling procedures and tables for inspection by attributes is a sampling system indexed by lot size ranges, inspection levels AQLs. The use of sampling schemes defined in this system will constrain the producer to provide product of quality at or better than selected AQL. Dodge Romig system, Dodge Romig sampling inspection tables are designed to minimize average total inspection for a given AOQL.
CONCLUSION Acceptance sampling is a statistical procedure used to determine whether to accept or reject a production lot of material. A wide variety of sampling plans are available.plans have an accepted AQL & a rejected LTPD & an AOQL. Acceptance sampling tables are there to supply a set of accepted procedures with known properties &verified results. Sampling provides rational means of verification that a production lot confirms with requirements of technical specifications.