Distinction between Quality and Reliability

Quality of a product is the degree of conformance to a set or specified standard for it. Quality can be for efficiency, accuracy of dimension, accuracy of surface finish, aesthetic standards etc. For example a component is specified with a dimension of say 10.0 ± 0.2. The component is manufactured and the dimension is then measured. If the actual dimension lies between 9.8 and 10.2, it is said that the component is of good quality otherwise of poor quality. Suppose you want a surface to be very smooth (1 micron roughness value). If the surface generated is not very smooth (i.e. it does not conform to the specified or desired degree) it is said to have poor quality. On the contrary if your requirements are a rough surface, then a component of rough surface is said to be of good quality.

In simple words reliability is 'Able to be trusted', or 'trustworthiness' particularly, in functioning of the system. Reliability can be defined in different ways in different contexts. A few examples are given below :

• In the Context of Equipment Health

Reliability of an equipment is the ability to function against failure, or

• In the Context of Production

Reliability of a machine is the ability to produce continuously good items, or

• In the Context of Measurement, Inspection and Quality Control

Reliability of measuring device is the ability to measure dimensions with equal accuracy or precision, etc.