Inspection may be carried out at the job place or in a separate inspection department. The location of inspection i.e. place of inspection depends on various factors e.g. types of materials to be inspected, process flows, types of inspection and testing machines and equipments etc. When the testing and inspection machines are to be kept in special rooms with various facilities — air conditioning, maintenance of temperature at certain level etc and they cannot be taken to the job place, materials, products, parts, components etc which are to be inspected, are taken from the normal flow to the inspection department or to such a place where such machines and equipment have been kept or installed. Thus, when materials, parts, products, components etc. are sent to the inspection department for inspection, it is called as central inspection. It is so because inspection is carried out at one central place only. Central inspection saves the time of inspectors, because they have not to move out in various departments for their work, but they receive in the inspection department, what they have to inspect. They have not to wait for the jobs to inspect. Moreover the inspectors can work freely without any pressure from the people, whose work they inspect. It makes possible the use of special inspection and testing machines and equipment.
But central inspection cannot be used to inspect heavy items and also huge quantity such as casting of 25 tonnes, an airplane, tons and tons of materials etc. It cannot be used in case of such products also, which pass continuously and automatically from one process to another or from one operation to another operation and the maintenance of continuous flow is a must. In such circumstances, inspection is done at the job place.
Moreover, in case of central inspection, materials are inspected, only when inspectors are available and therefore many a times, persons from various sections have to wait for a long time, to get the materials etc inspected. This lengthens the production cycle, because without inspection, the materials etc cannot be taken back for further operations. Materials, products etc are required to be taken to and from central inspection department several times, which increase the costs of handling and transportation. It also causes delay in production and it may happen that a large number of defective units may be turned out before the defect is discovered or final decision regarding acceptance or rejection is taken.
Inspection at the job place is used to resolve the problems mentioned in the preceding para. It is known as floor or patrolling or roving or first piece inspection. Here the inspectors move from one place to another place, or from one department to another department, or from one machine to another machine or from one process to another process etc to inspect materials, parts, components, tools, equipment, products during the various stages of production and the finished goods. They get the machines set right before production starts and also they catch defective work before a large quantity has been produced. Products of semi-automatic machines are also checked from time to time and results are recorded. If operators are found out of control, inspectors can advise to stop the machines before heavy losses have occurred. Corrective action is immediately taken to set the machines right.
This type of inspection saves time, money and labor. Materials, parts, semi-finished and finished products etc are not required to be handled and transported very often to and from central inspection place. Persons from various sections have not to wait in inspection department for getting materials, parts, products etc inspected. Thus time of production cycle becomes short to some extent.
But the persons of various sections, who want to get materials, parts, products etc inspected, have to wait till the inspectors come. The workers on the job have to wait for a green signal till the inspectors come and inspect their jobs, or work on production on their machines. They can start their work on machines after inspection is over and a green signal is received. Moreover, inspectors have to move to different places for inspection work with inspection tools. If the measuring or testing is delicate, it is not advisable and also possible to carry them everywhere. In such circumstances only central inspection is advisable.
Government agencies, responsible for quality and safety of regulated services, make use of roving inspectors considerably. Such inspectors have to visit various units at different distant places and therefore central inspection is not practicable in such cases.
For proper and reliable inspection and testing, the equipment and tools used for the same, should also be checked periodically and maintained properly. If this is not done, the results of inspection and testing may misguide the users and may prove useless. Sometimes, production is continued, even though the proportion of defective items in the total production is very high. Continuous production becomes necessary when (1) the item is badly needed for own use or (2) the item is badly needed for timely delivery to customers or (3) the defects can be removed by rework with a small cost.
Now, the suppliers for materials, parts, equipment etc are selected with great care after considering their past history, their reliability, volume of business, goodwill in market etc. If after inspection and testing of number of lots received from them, it is found that the lots are satisfactory, inspection can be reduced for goods received form such suppliers. It will save the cost of inspection and also the transportation and handling cost for returning the defective goods etc. It is not advisable to do away with inspection and testing of materials etc received from such suppliers but occasional inspection should be done. If during the occasional inspection, it is found that number of defective products are increasing with each next lot supplied, then the lot in which proportion of defects is beyond the upper limit, is rejected. Instead of occasional inspection of lots, each lot received from such suppliers is inspected.