Introduction To Reliability
Introduction to Reliability
In the previous chapters, we discussed the concept of quality management during the manufacture of products or the delivery of services. We used the concepts of subgroup statistics and control charts to measure or monitor quality at a specific moment in time. The question we were unable to answer was, “Will the product continue to perform its intended function as prescribed over the course of its life?”
Reliability is a measure of the extent to which the product will retain its quality over time. Rather than look at a snapshot of time, we consider the concept of quality over the long run. Reliable products are products you can depend on to function the way they are supposed to. Everything an organization does (from raw materials to design, manufacture, packaging, and shipping) can have an important effect on the reliability of the product over time. The concept of reliability has some implications in the service sector as well. Everything a travel agent does (from creating the vacation package, understanding the needs and expectations, negotiating rates, checking the quality of accommodation, food, etc.) can have a profound impact on the quality of the service experienced by all the members of a family during their vacation. When the product does not perform optimally during its life, there is a tremendous cost to the customer, and warranty costs to the manufacturer.
A hospital has hundreds of pieces of diagnostic equipment, devices, and tools that are put to everyday use in the course of providing care. Today, a patient entering a hospital will most likely come in contact with or use one of these: patient monitor, respirator, electroencephalograph (EEG), heart pacemaker, electrocardiograph (ECG), high voltage radio therapy equipment, x-ray equipment, defibrillator, anesthesia machine, heart pump, dialysis machine, suction pump, hyperthermia apparatus, or heart-lung machine. There is a steady growth in the number, variety, and complexity of these devices. Healthcare professionals depend on these devices for accurate diagnosis, monitoring, treatment, and examination. Have you ever contemplated what happens if they fail? What happens if your blood chemistry produces false or inaccurate test results? What happens if an important diagnostic device stops working altogether? Hospitals depend on these high-tech devices to provide accurate diagnosis so that the proper treatment can begin in a timely manner. In most cases, hospitals become concerned about product reliability issues only when the device fails at a particularly critical time, or when they become immersed in a litigation battle.
RELIABILITY
Reliability is the probability that a product will perform its intended function satisfactorily for a prescribed period of time when it is used under the specified environmental conditions. This definition presents four important considerations in the study of reliability.
1. Numerical Value
Reliability is a numerical value ranging between 0 and 1. For example, if the reliability of a mechanical pencil is 0.94, it means that the probability is 94% that the pencil will perform its intended function satisfactorily during its specified life under certain stated conditions. It also means that 94 of 100 pencils will perform, while 6 will not.
2. Intended Function
Most products are designed for particular applications. For example, a kitchen knife is not designed for opening canned products, nor is a screwdriver designed for opening paint cans. Kitchen knives are designed for cutting meat, vegetables, etc., and screwdrivers are designed for turning screws.
3. Intended Life of the Product
The intended life of a product is a function of usage, time, or both. For example, the intended life of automobile tires can be specified as 36 months or 36,000 miles. The intended life of a light bulb is stated as 2,000 hours.
4. Environmental Conditions
Certain products are designed for indoor use, outdoor use, or both. Certain types of ping pong tables are designed for both indoor and outdoor use, while others are designed for only indoor use. Certain medicines need to be stored at room temperature in order to preserve their potency.