Variability Basics - Causes of Variability
8 important questions on Variability Basics - Causes of Variability
True or false?
A: A nonpreemptive outage typically occurs between jobs, rather than during them, because we have some control as to exactly when they will inevitably occur.
B: A preemptive outage cannot occur between jobs.
A: True
B: False (i.e. a power outage could randomly occur during a setup that is in between jobs, but also during jobs)
Consider two (single machine) production stations in series (Penny Fab One). The first station is subject to random failures. It takes 0,5 hour to repair the machine and the number of failures are distributed with an average of 5 per day. Assume a production of 16 hours per day. What is the availability of station 1?
It takes 0,5 hour to repair the machine at station 1. So, MTTR = 0,5 hours
The time per day that the machine is up and running equals = 16 - (5 * 0,5) = 13,5 hours
Consequently, the MTTF equals: 13,5/5 = 2,7 hours
As a result, the avialability of the machine at station 1 equals: A = MTTF/ (MTTF + MTTR) = 0,5/ (0,5 + 2,7) =0.16
Explain the difference between Nonpreemptive Outages and Preemptive Outages.
Nonpreemtive Outages: represent downtimes that will inevitably occur but for which we have some control as to exactly when.
Preemptive Outages: Might be caused by catastrophic failure of a machine or when the machine becomes radically out of adjustment, forces a stoppage whether or not the current job is completed.
- Higher grades + faster learning
- Never study anything twice
- 100% sure, 100% understanding
For my 1st exam I got a C. Then, I started looking for ways to learn better and I came across Study Smart. Since then I have scored a A+, A, A- and another A. I highly recommend it to everyone who wants to hear it. I am so happy with it!!
I was struggling to finish all my first-year subjects for 3 years. Then I discovered Study Smart, which helped me to finish all of them within 3 months.
Because of StudySmart, things are going well in many ways. Before, I always had study stress and no time for anything. Now I feel calm and confident (because of the program). I used to score a B, now I usually score an A or A+.
Hey Chris, I really want to thank you very much for developing the platform, I usually got around C for my exams, now I scored an A+, an A and a A- !!
Since using Study Smart, my average has increased significantly. I even completed a statistics course with a A+ while I'm bad at statistics. I took on extra courses this year, because of Study Smart. Thanks so much!
Ever since I started studying with StudySmart I passed all my exams !!! No more re-sits!! At first, I was happy with a pass and now I only get good grades. Many thanks!
I aced all the courses I studied with Study Smart. For law, I first scored a D, and now an A! I’m 100% sure that I’ll pass all the courses I study with Study Smart.
I always thought I studied well. My grades were fine. I could never have imagined that applying these study skills would have such a huge and direct impact on my grades, my speed and the pleasure I have in learning.
For the first time, I finally feel totally confident about the way I learn. I have the perfect overview and make great progress in terms of speed and the grades I get. Thanks, Chris!
I immediately started to enjoy learning again, and my grades soared. All of a sudden, everything went better. I highly recommend Study Smart to all students..
Being able to create my materials online made the process of studying so much smoother and quicker. I no longer have to spend a huge amount of my time on creating my summaries.
At first, my notes were a mess. Now I use Study Smart to take my notes in a perfectly structured way. It helps me to save a lot of time and do other things I enjoy.
Students that study with Study Smart get better grades. The system applies all the learning methods in such a way that both well-performing students and students who struggle perform much better.
Hi Chris, I would like to thank you very much. Last year I scored C on a course, and this year I got an A+ thanks to your method! Thank you very much!
The largest effect is that my child is more enthusiastic about school! Every parent wants their children to be happy at school, Study Smart made it happen.
In high school, I failed several exams, and that has really changed now. I actually needed this tool very much back then. Since I started studying with StudySmart, I haven't had any D's. My average score is now an A and those are results I would have never had in the past
With my old method, I passed only 3 out of 8 courses. Since I started taking my notes digitally in Study Smart, I have passed all my courses on the first try. For me, StudySmart takes away the stress of wondering if I will pass or not.
Thanks to StudySmart, I passed all my exams, and with better grades than before! On top of that, I have mastered a very good study method now, which I am confident will help me earn my degree.
Does describe a complete relationship between effective mean process time and natural mean process time?
Not fully, since there still relatively small detractors not considered in this relationship (i.e. operator unavailability). This means that could be underestimated when using this formula.
Suppose a machine is just repaired and starts working again at 1 PM. The machine works fine and is turned off at 5 PM. The next day it is turned on again at 8 AM and it breaks down at 1 PM. Is the time to failure 24 hours, or 9 hours?
9 hours, MTTF (or 'TTF' here, since we only have 1 failure) does not include time when a machine is off. (Can a machine fail if it is not doing anything?)
Does it matter for the SCV of effective mean process times if the availability is 80% or 20% (considering all other things being equal)? Does it matter in any other way?
1: No. Consider formula 8.6. 0,2 (1-0,2) = 0,8 (1-0,8)
2: Of course. An availability of 0,2 will have considerably less throughput for the same system as an availability of 0.2.
What is the CV of process times for a system that has exponentially distributed process times and no downtimes?
No downtime means 100% availability ->
Exponentially distributed process times -> CV = 1
Consider formulas 8.7, 8.8 & 8.9 for variability from nonpreemptive outages. Now consider a system that is totally equivalent, but also suffers from variability from rework. Obviously from 8.4.4 you should use the same formulas, but different values. Which value changes in these formulas?
Ns decreases (in comparison to the first situation there will be less parts produced in between setups).
Try our study magic for free
a PDF, study it super fast
- No sign up, email or credit card needed!
- AI makes unlimited flashcards
- Get unlimited quizzes and tests
- Ask AI anything
- No sign up, email or credit card needed!
- Have and keep perfect overview
- Make flashcards, notes and mind maps
- Review, test and score!
The question on the page originate from the summary of the following study material:
- A unique study and practice tool
- Never study anything twice again
- Get the grades you hope for
- 100% sure, 100% understanding
