HOME  |  NEWS  |  BLOGS  |  MESSAGES  |  FEATURES  |  VIDEOS  |  WEBINARS  |  INDUSTRIES  |  FOCUS ON FUNDAMENTALS
  |  REGISTER  |  LOGIN  |  HELP
Comments
View Comments: Newest First|Oldest First|Threaded View
Page 1/5  >  >>
lchien52
User Rank
Bronze
Re: Which is more accurate?
lchien52   5/3/2013 10:50:57 AM
NO RATINGS
the quartz analog clocks rely on an inexpensive quartz crystal which is probably+/-100 ppm, typically probably 20 ppm.

The AC synchronous motor clocks rely on the power company. I think most of the major AC power grids litteraly count the number of cycles in an hour and speed up or slow down slightly every hour to make the long term stability way better even than the short term stability. So that there are exactly 5,184,000 cycles in a day (60 Hz US standard).

 

 

Rob Spiegel
User Rank
Blogger
Re: The things we get used to
Rob Spiegel   1/31/2012 3:02:21 PM
NO RATINGS
Yes, Bpark, in the story it was a two-stroke. A dirt bike if I remember right. That would make sense. So the engine doesn't care what direction it turns. That must be quite surprising when it happens.

bpark1000
User Rank
Iron
Re: The things we get used to
bpark1000   1/30/2012 9:32:36 PM
NO RATINGS
2 stroke engines with reed valve intakes can run in either direction.  One of my friends would start up model airplane engines, and they would sometimes get going the wrong way.  He would throw a rag into the propeller to stop the engine so it could be restarted.  So the bike engine running backwards is no mystery, if it's 2 stroke.

jwillsey
User Rank
Iron
Re: The things we get used to
jwillsey   1/30/2012 6:30:15 PM
NO RATINGS
I assumed the DC adapter was for another appliance plugged into the same outlet as the clock.

I cannot imagine the adapter causing the grinding sound. My first thought is of a poor service connection. Plugging in the adapter caused an intermittant connect-disconnect (sparking) of the 110v service to the outlet. If you caught this motor just right, it could reverse it. You may also hear it as chatter or grinding in the clock. Not a safe condition.

bpark1000
User Rank
Iron
Re: The things we get used to
bpark1000   1/30/2012 12:34:59 AM
NO RATINGS
DC adaptor?  I thought the synchronous motor was run directly from the AC line.

Jack Rupert, PE
User Rank
Platinum
Re: The things we get used to
Jack Rupert, PE   1/28/2012 2:22:38 PM
NO RATINGS
That sounds like an extremely plausible explanation bpark1000.  What do you think caused to correct itself when the DC adapter was plugged in?

Rob Spiegel
User Rank
Blogger
Re: The things we get used to
Rob Spiegel   1/12/2012 12:24:22 PM
NO RATINGS
That makes sense, Bpark. We had an entry in the Made by Monkeys section by the owner of a small motorcycle. He told the story of his bike starting backwards. Same concept, I guess.

William K.
User Rank
Platinum
Time ticks in reverse: clock runs backwards
William K.   1/11/2012 11:12:34 PM
NO RATINGS
I had an analog alarm clock that developed a similar tendancy to run the wrong way. What I found is that it had a synchronous motor that was equally comfortable starting and running in either direction, and it used a rachet mechanism to force it to only run in the desired direction. When the grease on the rachet mechanism thickened a bit it kept the rachet dog from engaging the wheel, and so the motor could now rotate in either direction. 

bpark1000
User Rank
Iron
Re: The things we get used to
bpark1000   1/11/2012 5:46:09 PM
NO RATINGS
There is no mystery at all why the clock ran backwards.  There is a type of motor where the rotor is a permanent magnet inside an AC pole structure  (like a "standard" synchronous motor).  If the rotor is light enough, its vibration amplitude at 60 Hz will exceed a pole pitch.  Such a synchronous motor will spontaneously start in a random direction.  A ratchet mechanism forces it to reverse if it starts in the wrong direction.  The drop damaged this mechanism, allowing the motor to start backwards.

Ratsky
User Rank
Platinum
Re: Which is more accurate?
Ratsky   1/11/2012 3:32:04 PM
NO RATINGS
You mean you don't just keep everything on GMT <vbg>? I only have about 6 or 7  "conventional" clocks (microwave, oven, coffe maker, cordless phones, ancient clock radio and an old VCR, etc.)  and I just take my cellphone (the Verizon one, the AT&T Blackberry is way off) around with me.

Page 1/5  >  >>


Partner Zone
Latest Analysis
Melissa Cavanagh of 3DP Unlimited talked to Design News about the company’s large format 3D printer, during Medical Design and Manufacturing Midwest.
The DDV-IP is a two-wheeled self-balancing robot that can deliver cold beverages to thirsty folks on hot summer days. A wireless RF remote enables manual control of the device beyond the act of self-balancing. All of the features of the DDV-IP result in an effective delivery vehicle while providing entertainment to the user.
Eric Doster of iFixit talks about the most surprising aspect of the Microsoft Surface Pro 3 teardown. In a presentation at Medical Design & Manufacturing Midwest, iFixit gave the Surface Pro 3 a score of one (out of a possible 10) for repairability.
Barnacles and mussels stay attached to ship hulls and rocks because of a very sticky protein glue they secrete, holding on for a long time even underwater. Researchers at MIT took mussel glue as inspiration -- and as an ingredient -- for engineering their own sticky waterproof adhesive.
Automation technology advances matched with expanded fracking and the growing urbanization of Asia, South America, and the Middle East, are fueling a boom in the automation industry.
More:Blogs|News
Design News Webinar Series
10/7/2014 8:00 a.m. California / 11:00 a.m. New York
9/25/2014 11:00 a.m. California / 2:00 p.m. New York
9/10/2014 11:00 a.m. California / 2:00 p.m. New York
7/23/2014 11:00 a.m. California / 2:00 p.m. New York
Quick Poll
The Continuing Education Center offers engineers an entirely new way to get the education they need to formulate next-generation solutions.
Oct 20 - 24, How to Design & Build an Embedded Web Server: An Embedded TCP/IP Tutorial
SEMESTERS: 1  |  2  |  3  |  4  |  5  |  6


Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.
Next Class: 10/28-10/30 11:00 AM
Sponsored by Stratasys
Next Class: 10/28-10/30 2:00 PM
Sponsored by Gates Corporation
Learn More   |   Login   |   Archived Classes
Twitter Feed
Design News Twitter Feed
Like Us on Facebook

Sponsored Content

Technology Marketplace

Copyright © 2014 UBM Canon, A UBM company, All rights reserved. Privacy Policy | Terms of Service