Basic Reliability

What is Reliability?

Reliability and Quality

Quality and Reliability go hand-in-hand, you cannot have quality without reliability and likewise, you cannot have reliability without quality.  Please do not confuse one with the other, they are two separate entities. 

We know that the quality of a product is determined in the design stages of the product.  Quality is defined as the totality of features and characteristics of a product or service that bear on its ability to satisfy a specific need or an implied need.   The quality of a product must meet the specifications when required by the user.  

Quality can be defined as fitness for use, customer satisfaction, or conformance to requirements.   Conformance states that a product will meet the specifications. 

Reliability states or implies a probability that a product will meet the specifications under certain conditions for a specific period of time.   Quality can be said to be based on reliability and the confirmation to the users demand.

Reliability, deals primarily with the calculation of product life as well as product failure.  Please take note that no one can calculate the exact failure period that equipment will fail.  All we can do is to calculate the probability that equipment will fail in a given period of time. 

The formal definition of Reliability is, “the probability that a product will perform its intended mission for a certain period of time under given conditions”.

Lets consider the age old question, “is quality and reliability the same thing?”
We can better explain this by looking at an example of quality versus reliability.

Quality Perspective:

A fire alarm system is delivered from the factory to the installation contractor. The contractor finds that the poor quality level, (units that won''t work) is approximately 100 PPM due to perhaps to "manufacturing errors and infant mortality".

Reliability Perspective:

A fire alarm system has a 99.999999% probability of operating over a six-month period, when properly installed and tested inside of an occupied residential dwelling.

Or a more comprehensive definition would be: 

The level of confidence on the conditional probability, specifications and performance criteria for operating and testing, a detailed environment specification for relative humidity, temperature ranges, etc., the age of the system upon installation and operational stress levels.

So, we can conclude; that “Reliability” is a measurement of “Quality” over some period of time.

There are four key factors of Reliability:

Probability
Intended Function
Time
Environment

The performance aspect of product reliability involves planning, manufacturing, testing and maintaining the product to achieve maximum reliability.  The reliability of a part depends absolutely on how well reliability is planned into the product in the early design stages. This is referred to as Design for Reliability. Strict quality control, which includes inspections, checks, and tests, should be utilized in order to achieve a higher level of reliability.

So if you are using an outside supplier, a vendor, or an OEM (Original Equipment Manufacturer) be sure and work closely with the reliability and or quality engineers of the contracted company or business.   That way, you can keep in a closed-loop of the things that cause manufacturing or field failures, which would compromise the reliability of your product.    It would help to review all of the data of the design tests, manufacturing tests and reliability tests done at the supplier.  Then you may investigate what caused the types of failures of the product as well as the corrective actions implemented to prevent it from happening again.

The Benefits of a Reliability Program

Advantages and benefits of reliability programs may be recognized in many ways.  Savings associated with various manufacturing distribution and quality related processes might be identified and maximized through reliability programs.  The impact of product performance in safety critical applications can also be quantified and engineered.  Some examples of reliability program benefits are;

1)         The company can match the capabilities of product design to the needs and  applications of the customer’s environment and performance expectations.&