Deck 16: Maintenance and Reliability

Question 1

The objective of maintenance and reliability is to maintain the capability of the system.

Answer 1

True

Question 2

If the mean time between failures has been calculated to be 2,000 hours, then FR(N) = 0.005 failures/unit-hour.

Answer 2

False

Question 3

Reliability is the probability that a machine part or product will function properly for a specified time regardless of conditions.

Answer 3

False

Question 4

The Orlando Utilities Commission uses a computerized maintenance management program and devotes significant dollar and labor resources to power plant maintenance, because the costs of unexpected failure are incredibly high.

Question 5

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

Question 6

Define reliability.

Question 7

Which of the following is a reliability tactic?

A) improving individual components
B) F increasing repair speed
C) providing redundancy
D) A and C
E) A, B, and C

Question 8

Define maintenance.

Question 9

The MTBF (mean time between failures) is calculated as the reciprocal of the number of failures during a period of operating time.

Question 10

Which of the following statements about maintenance at the Orlando Utilities Commission is FALSE?

A) There are at least two types of preventive maintenance, including an annual maintenance and a less frequent overhaul schedule.
B) Its preventive maintenance program has earned the company top rankings and its competitive advantage.
C) Each power-generating unit is taken off-line every three years for a complete overhaul.
D) Each of its power-generating units is taken off-line for maintenance every one to three weeks.
E) Costs associated with breakdowns are several times higher than costs arising from preventive maintenance.

Question 11

________ is the probability that a machine part or product will function properly for a specified time under stated conditions.

Question 12

________ consists of all activities involved in maintaining capability of the system.

Question 13

The objective of maintenance and reliability is to:

A) ensure that breakdowns do not affect the quality of the products.
B) ensure that no breakdowns will ever occur.
C) ensure that preventive maintenance costs are kept as low as possible.
D) maintain the capability of the system.
E) ensure that maintenance employees are fully utilized.

Question 14

Maintenance includes all activities involved in maintaining capability of the system.

Question 15

At the Orlando Utilities Commission, overhauls are scheduled for summer and winter.

Question 16

Identify the two reliability tactics and the two maintenance tactics.

Question 17

The product failure rate FR(%) is the percent of failures among the total number of products tested.

Question 18

The reliability of a system in which each individual component must function in order for the entire system to function, and in which each component has its own unique reliability, independent of other components, is the sum of the probabilities of each of those components.

Question 19

What is the probability that a product will function properly for a specified time under stated conditions?

A) functionality
B) maintenance
C) durability
D) reliability
E) fitness for use

Question 20

The reliability tactics include implementing or improving preventive maintenance as well as increasing repair capabilities or speed.

Question 21

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

Question 22

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. What is the reliability of this job?

A) 91.27%
B) 94.11%
C) 97.00%
D) 98.00%
E) 99.00%

Question 23

Twenty high-technology batteries are tested for 200 hours each. One failed at 20 hours; another failed at 140 hours; all others completed the test. FR(%) is ________ and MTBF is ________.

A) 20%; 880 hours
B) 10%; 3760 hours
C) 20%; 3760 hours
D) 10%; 1880 hours
E) 80%; 920 hours

Question 24

A redundant part or component increases reliability because it is connected in parallel, not in series.

Question 25

Suppose that a process is comprised of five components, each having an 85% success rate. By how much would reliability change if the process switched from having the components in parallel to having the components in series?

A) no change
B) 100% increase
C) 55.6% increase
D) 55.6% decrease
E) 36.3% decrease

Question 26

Ten high-technology batteries are tested for 200 hours each. One failed at 50 hours; all others completed the test. FR(%) is ________ and FR(N) is ________.

A) 10%; 1/1850
B) 10%; 1/2000
C) 25%; 1850 hours
D) 90%; 1/2000
E) 10%; 1/1950

Question 27

As the number of components in a system connected in a series increases, all other things being equal, the reliability of the system usually:

A) increases.
B) stays the same.
C) decreases.
D) increases, then decreases.
E) decreases, then increases.

Question 28

A system has three components in parallel with reliabilities 0.9, 0.7, and 0.6. What is the system reliability?

A) 0.378
B) 0.733
C) 0.988
D) 0.985
E) 2.200

Question 29

A system is composed of three components A, B, and C. All three must function for the system to function. There are currently no backups in place. The system has a reliability of 0.966. If a backup is installed for component A, the new system reliability will be:

A) unchanged.
B) less than 0.966.
C) greater than it would be if a backup were also installed for component B.
D) greater than 0.966
E) none of these

Question 30

A system has three components in series with reliabilities 0.9, 0.7, and 0.8. What is the system reliability?

A) 0.315
B) 0.500
C) 0.800
D) 0.504
E) 2.400

Question 31

MTBF measures the average:

A) calendar time between failures.
B) operating time between failures.
C) number of failures per unit time.
D) number of operations between failures.
E) downtime per breakdown.

Question 32

A two-component process has a 90.25% success rate in series and a 99.75% success rate in parallel. If each component has the same reliability, what is the reliability of an individual component?

A) 50%
B) 90%
C) 95%
D) 99%
E) 97%

Question 33

Ten high-technology batteries are tested for 200 hours each. Two failed at 20 hours; all others completed the test. FR(%) is ________ and MTBF is ________.

A) 20%; 1/820
B) 80%; 1/820
C) 80%; 820 hours
D) 20%; 820 hours
E) 20%; 2000 hours

Question 34

A redundant part decreases reliability if the reliability of the redundant part is lower than that of the part it is backing up.

Question 35

How is MTBF related to FR(N)?

A) MTBF is measured in hours, while FR(N) is measured in years.
B) MTBF is normally distributed, with FR(%) as its mean and FR(N) as its standard deviation.
C) MTBF is the reciprocal of FR(N).
D) Both MTBF and FR(N) increase when breakdown maintenance is replaced by preventive maintenance.
E) MTBF and FR(N) are unrelated concepts.

Question 36

Components A, B, and C are connected in series. Component D is connected in parallel to component B. Which of the following statements is TRUE?

A) The system works only if A works, B or C works, and D works.
B) Component B must work for the system to work.
C) The system works when A works, C, works, and either B or D works.
D) Components B and C are backups to A.
E) The system works if D works, and any of A, B, or C works.

Question 37

What is the reliability of the three components connected in series shown below?

A) 0.799425
B) 0.85000
C) 0.91333
D) 0.95000
E) 2.79

Question 38

Consider a product with three components in series, with reliabilities of 0.90, 0.80, and 0.89 for components A, B, and C, respectively. Furthermore, component B uses a backup that also has a reliability of 0.80. What is the reliability of the system?

A) 0.50000
B) 0.71280
C) 0.76896
D) 0.85536
E) 3.49000

Question 39

What is the reliability of a four-component product, with components in series, and component reliabilities of .90, .95, .96, and .99?

A) 0.8295
B) 0.90
C) 0.955
D) 0.8126
E) 0.945

Question 40

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 an 80% reliable backup at K. This backup will change the system reliability from ________ to ________.

A) 0.9762; 0.9605
B) 0.9605; 0.9762
C) 0.9605; some smaller value
D) 0.9605; 0.996
E) 0.98; 0.99

Question 41

Ten high-intensity bulbs are tested for 100 hours each. One failed at 10 hours; all others completed the test. Calculate FR(%), FR(N) and MTBF.

Question 42

A system is composed of 100 identical parts. All must function for the system to function. Each component has a reliability of 0.99. What is the system reliability?

A) 0.366
B) 1
C) 0.999
D) 99
E) 0.886

Question 43

Explain carefully how redundancy improves product reliability.

Question 44

A product is composed of a series connection of four components with the following reliabilities. What is the reliability of the system?

Question 45

A system has 12 components in series. Each component has a reliability of 0.95. What is the reliability of the system?

Question 46

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 40 of these batteries for 72 hours. One failed at 39 hours; one failed at 62 hours; one failed at 70 hours. All others completed the test. Calculate FR(%), FR(N), and MTBF.

Question 47

What is the impact on system reliability of adding parts or components in parallel?

Question 48

________ is the expected time between a repair and the next failure of a component, machine, process, or product.

Question 49

The diagram below identifies the elements of service as provided by a soft drink vending machine. Each element has an estimate of its own reliability, independent of the others. What is the reliability of the "system"?

Question 50

A system consists of four components in series. The reliability of each component is 0.96. What is the reliability of the system?

Question 51

The inverse of the mean time between failures is the ________.

Question 52

A system has four components in a series. What is the reliability of the system?

Question 53

Ten high-intensity bulbs are tested for 100 hours each. One failed at 40 hours; another failed at 70 hours; all others completed the test. Calculate FR(%), FR(N), and MTBF.

Question 54

________ is the use of a component in parallel to raise reliabilities.

Question 55

"High reliability can be achieved in a product without having high reliability in the component parts. In fact, any reliability target, no matter how high, can be achieved with only mediocre parts, so long as enough of them are present." Discuss; an example may help.

Question 56

The Everstart is a battery with an intended design life of 72 months. Stephanie Bradley recently put five of these batteries through accelerated testing (the company couldn't wait six years) to simulate failure patterns. The test results had one failure at 26 months, one failure at 32 months, one failure at 50 months, and one failure at 62 months. Calculate FR(%), FR(N), and MTBF.

Question 57

Increasing the number of parts or components in a product tends to reduce its reliability. Why is this true only when adding components in series?

Question 58

What is FR(N)? How is it calculated? How are FR(N) and MTBF related?

Question 59

Twenty high-intensity bulbs are tested for 100 hours each. One failed at 80 hours; one failed at 90 hours; all others completed the test. Calculate FR(%) and FR(N).

Question 60

The academic service commonly referred to as "registration" consists of several smaller components: advising, registration for courses, fee assessment, financial aid calculations, and fee payment. Each of these modules operates independently and has some probability of failure for each student. If the five probabilities that accompany these services are 95%, 90%, 99%, 93%, and 99%, respectively, what is the "reliability" of the entire product from the student's perspective, i.e., the probability that all five will work according to plan?

Question 61

When identifying the optimal maintenance policy, the cost of inventory maintained to compensate for the downtime is a cost often ignored.

Question 62

The MTBF distributions of products, machines, or processes that have "settled in," or gone beyond the infant mortality phase, often follow the exponential distribution.

Question 63

Suppose that a three-stage process in a nuclear reactor had reliability ratings of .98 at each station and that only one stage needed to be successful for the process to work. If the plant wants to establish 6-sigma standards (≤ 3.4 defects per million), what % reliable redundant controls need to be added to each station?

Question 64

Electronic sensors have proven so effective that preventive maintenance is no longer necessary.

Question 65

Suppose that a three-stage process had reliability ratings of .7, .8, and .9 at each station and that a failure at any station represented a failure for the entire process. If each station is given a redundant check with the same reliability as the original component, what is the increase in system reliability?

Question 66

A component must have reliability of .999. Two technologies are available for this component: one produces a component with .999 reliability at a cost of $3000. Another produces a component with .75 reliability at a cost of $500. Which is cheaper: one high quality component or a parallel set of inferior components?

Question 67

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

Question 68

A product has four components A, B, C, and D. The finished product must have a reliability of at least .95. The first three components come from a supplier, and they have reliabilities of .99, .98, and .995, respectively. The fourth component is being designed now. What must the reliability of component D be in order to meet the product reliability condition?

Question 69

A product has three components X, Y, and Z. Product X has reliability of 0.991, and Y has reliability of 0.993. If Z has reliability of 0.991, what is the reliability of the entire product? Can Z be redesigned to be reliable enough for the entire product to have reliability of 0.99? Explain.

Question 70

The "full cost view of maintenance" results in more firms choosing a policy of breakdown maintenance, when compared to the "traditional view of maintenance."

Question 71

Preventive maintenance implies that machine sensors to detect variations from normal are inadequate.

Question 72

A simple electrical motor has three components: windings, armature, and housing. These three components have reliabilities of .993, .95, and .999. There is no possibility of redundant parts. The motor must have an overall reliability of at least 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.

Question 73

Small standard deviations in the MTBF distribution of a machine tend to support a policy of preventive maintenance for that machine.

Question 74

Preventive maintenance implies that we can determine when a system needs service or will need repair.

Question 75

An optimal maintenance policy strikes a balance between the costs of breakdown and preventive maintenance so that the total cost of maintenance is at a minimum.

Question 76

Preventive maintenance is reactive.

Question 77

Recording the maintenance history of processes, machines, or equipment is important for preventive maintenance, but largely irrelevant for breakdown maintenance.

Question 78

General Grant must send orders to General Butler. Carrier pigeons are the medium of choice. A single pigeon has a .7 probability of arriving at the proper destination in a timely fashion. How many pigeons, each carrying an identical set of orders, must Grant send in order for him to have 98% confidence that the orders reached General Butler?

Question 79

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.

Question 80

Preventive maintenance is nothing more than keeping the equipment and machinery running.