Exam 20: Maintenance and Reliability

A system has three components in parallel with reliabilities 0.9, 0.7, and 0.5. System reliability is

A high school senior is seeking admission into her state's flagship university. The admission requirements are as follows. The student must meet at least ONE of the criteria A, B, C. The student must meet criterion D. These criteria are detailed below. And the student must file a complete application, file a medical form, and pay an application fee by a stated date. A: score a composite 28 on the ACT exam B: have a high school GPA of 3.0 or greater C: place in the top ten percent of the high school class D: complete all courses in the state-mandated "core college preparatory" curriculum (CCPC); OR complete all but one course in CCPC with a 3.5 GPA on all CCPC courses taken. Using the tools of reliability analysis with redundancy, translate these conditions into the appropriate reliability schematic.

Adding an additional part to a component or product ordinarily reduces reliability by introducing an additional source of failure.

Explain carefully how redundancy improves product reliability.

Infant mortality refers to the high failure rate often encountered in the very early stages of the lifetime of a product.

Describe how Orlando Utilities Commission obtains competitive advantage through its maintenance practices.

While breakdowns occur randomly, their frequency is somewhat predictable through such tools as the product failure rate, MTBF, and the breakdown costs model.

Why is it that many cases of infant mortality of products are not due to product failure?

A simple electrical motor has three components: windings, armature, and housing. These three components have reliabilities of .97, .992, and .999. There is no possibility of redundant parts. The motor must have an overall reliability of 0.980, according to the product line manager who will use the motor as an input. What would you do to redesign the motor to meet this specification? Discuss, including a recalculation to meet the standard.

Preventive maintenance is reactive.

Maintenance includes all activities involved in keeping a system's equipment in working order.

A simple electrical motor has three components: windings, armature, and housing. These three components have reliabilities of .9998, .9992, and .9999. There is no possibility of redundant parts. What is the reliability of the motor? Round your answer to four decimal places.

DuLarge Marine manufactures diesel engines for shrimp trawlers and other small commercial boats. One of their CNC machines has caused several problems. Over the past 30 weeks, the machine has broken down as indicated below. Each time the machine breaks down, the firm loses an average of $3,000 in time and repair expenses. If preventive maintenance were implemented, it is estimated that an average of only one breakdown per week would occur. The cost of preventive maintenance is $1,000 per week. Number of breakdowns per week 0 1 2 3 4 Frequency (Number of weeks that breakdowns occurred) 8 3 5 9 5 What is the weekly total maintenance cost of this program?

How do expert systems improve maintenance systems?

A system is composed of four parts, J, K, L, and M. All four must function for the system to function. The four component reliabilities are .99, .98, .992, and .998. The designers are considering putting a .80 reliable backup at K. This backup will change the system reliability from __________ to __________.

Century Digital Phone advertises phone battery life (on standby) of up to three days. The standard deviation is thought to be five hours. Tina Talbot, an employee at CDP, tested 10 of these batteries for 72 hours. One failed at 40 hours; one failed at 62 hours; one failed at 70 hours. All others completed the test. Calculate FR(%), FR(N), and MTBF.

A product design team is preparing to build a new doohickey. A doohickey consists of one A module, one B module, and one C module. There are different versions of these modules available in the company's design library. For example, there are two choices for A: A1 is .99 reliable, while A2 is .975 reliable. The table below details the choices available, along with the cost of each choice. Module variation Reliability Cost, each A1 99 \ 17 A2 975 \ 10 1 995 \ 4 2 992 \ 3 1 98 \ 2 2 90 \ 0.50 3 60 \ 0.25 Help the design team by selecting the least costly version of a doohickey that has system reliability of at least .96. Draw a schematic of your finished design.

A job consists of a series of three tasks. Task 1 is performed correctly 98% of the time, task 2 is performed correctly 99% of the time, and task 3 is performed correctly 97% of the time. The reliability of this job is

Suppose that a manufacturing plant is considering contracting out some preventative maintenance work. For $2000 each year a firm would cover all breakdowns free of charge and provide preventative maintenance. Two other options exist that entail the use of regular employees however. The first is to skip preventative measures and simply fix breakdowns, which occur at a rate of 2/year. Each breakdown costs about $750 to fix. The final option is to divert excess labor capacity to preventative measures, which reduces the chance of a breakdown per year by Y% given X hours of preventative maintenance subject to Y=10X-X^2. If each preventative maintenance hour costs $50, which option should the firm choose?

If the mean time between failures has been calculated to be 2,000 hours, then FR(N) = 0.0005 failures/unit-hour..