http://www.physorg.com/news/2011-06-power-grid-disrupt-clocks.html
Since 1930 the grid has been held as close to 60 hertz as possible so electric clocks and such will be accurate.
Now they are going to try an experiment which will disrupt the accuracy, let it freewheel.
I know in my industry, electric motors run at a certain RPM based on that frequency, if that frequency is off, some industrial processes will run awry, anybody have any thought on this? They say keeping accurate frequency is too expensive, they want to save money by cheapening the power.
Originally posted by sonhouseI didn't know any clocks relied on power grid frequency for their timing.- but then again I don't know any clocks that don't run off batteries. (except the computer).
Since 1930 the grid has been held as close to 60 hertz as possible so electric clocks and such will be accurate.
In Zambia, we have power cuts so often that such clocks would be useless anyway (unless they are just used for timing a process and not for keeping time.
Originally posted by twhiteheadI think the time for power line based accuracy has gone by in the US. My main question is if industry will suffer, motors that run at a certain known RPM and process machines designed with that specific RPM in mind, if that changes, will the processes depending on that also change?
I think the real question is whether other countries are as careful about their power, and if not, are products that depend on it only used in the US?
Modern day clocks with quartz movements are more accurate in the short term but in the long term, power line frequency is more accurate.
There is no updating a regular quartz clock. I have a couple, including a Casio wristwatch, that gets timing updates by a radio signal at 60 Kilohertz, a very low frequency but a transmitter in Fort Collins Colorado transmits time updates several times a day and therefore my wristwatch is as accurate as an atomic clock. Again, not in the short term, an hour or minute, but in the long term, it catches up with the atomic clock then freewheels for some hours then updated again, and so forth.
Short term, atomic clocks are much more accurate and also in long term but they can't send directly the atomic timing signal accurately.
When I was with Apollo, we could start the atomic clocks into a rough sync, by using WWV, a short wave radio station that broadcasts atomically accurate time hacks in english once a minute on several shortwave frequencies, 5, 10, 15, 20 megahertz and maybe a few more.
Canada has another time standard on 7.335 Kilohertz, updated in French.
The problem with using those kind of signals and 60 Kilohertz also, is the path length changes from second to second, the path between the transmitter and the receiver. That means a corresponding change in the time position of a time hack. Not much mind you, for setting a wristwatch or house clock, it gives more than enough accuracy for any home use but for syncing of an atomic clock, it is just a rough in.
I could expound on just what that signal is like but it is involved and there probably not be a huge amount of interest in the subject. Just know you can rough sync an atomic clock with radio signals but not a real sync, that has to be done with other means.
Originally posted by sonhouseMy understanding from the article is that the change may result in tens of seconds difference every 24 hours. I don't think that kind of difference will affect the RPM of motors to the point of causing any problems.
I think the time for power line based accuracy has gone by in the US. My main question is if industry will suffer, motors that run at a certain known RPM and process machines designed with that specific RPM in mind, if that changes, will the processes depending on that also change?
I could expound on just what that signal is like but it is involved and there probably not be a huge amount of interest in the subject. Just know you can rough sync an atomic clock with radio signals but not a real sync, that has to be done with other means.
I would think that the best solution for serious timekeeping would be GPS. My understanding is that time is very important to GPS and in therefore very accurate. It might however be too expensive for a wristwatch.
Originally posted by twhiteheadThat is what I hope to come out of this experiment, to show industrial processes to be unaffected by this change.
My understanding from the article is that the change may result in tens of seconds difference every 24 hours. I don't think that kind of difference will affect the RPM of motors to the point of causing any problems.
[b]I could expound on just what that signal is like but it is involved and there probably not be a huge amount of interest in the subject. ...[text shortened]... tant to GPS and in therefore very accurate. It might however be too expensive for a wristwatch.
GPS signals are modulated by having atomic clocks aboard each GPS satellite so they already have precision time keeping onboard.
There is work being done now to make atomic clocks the size of a cube of sugar and a thousand times cheaper than the Hewlett Packard versions and such available now. It is conceivable they could in fact be incorporated into a watch in ten years or so. But for regular home use, the radio updated clocks are as good as people would ever need in any daily circumstance like keeping class schedules or TV shows or alarm clocks or whatever.
I doubt very much that outside of GPS work, atomic level clocks would ever be needed for home use. Of course that may just be my lack of imagination, there could be apps that could come about by clever dudes in the future requiring extremely accurate timing. Don't know what but it could happen.
Tens of seconds in 24 hours, say 20 seconds in one day, would be equivalent to about one part in 4000 inaccuracy in the RPM's of a motor. 24 hours is 86,400 seconds so ten seconds in 24 hours would be one part in 8640, 20 seconds would be one part in 4320, so the RPM would change by that much, if a motor was running at 4320 RPM by basic design, it would be off by one RPM. I guess we could live with that! I think that analysis is correct, maybe you could go through it yourself to find if it is wrong.
Have I gone mad, or am I missing something here?
What a bonkers idea, using the mains frequency as a method of keeping time.
Here in the UK, most devices rectify the mains voltage from AC to DC and then have a whacking big capacitor to smooth out the ripple, what is left is a nice (not pure 100hz ripple free) DC voltage.
Anything in my home that has a clock uses the above method.
As for non-rectified devices that use straight mains AC, slight variations won't mean a thing (kettles, vacuum cleaners and the like).
In situations where RPM has to be very accurate, you would never ever rely on just the raw mains frequency, that would be bonkers.
Also for a computing device, the voltage has been rectified to an extreme level.
I think we have a situation here where the advisor's should perhaps go back to working in burger outlets.
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Originally posted by WoodgieThat's what I was thinking. There are so many things that can influence the exact specs of the mains one way or another (tea kettles in the world cup final break!) that anyone relying on precision from that source is a gambler.
In situations where RPM has to be very accurate, you would never ever rely on just the raw mains frequency, that would be bonkers.
Richard
Originally posted by Shallow BlueFor the most part it is very accurate if the power company ensures the accuracy of the sine wave sent to the house or business. That's what they have been doing for decades in the US.
That's what I was thinking. There are so many things that can influence the exact specs of the mains one way or another (tea kettles in the world cup final break!) that anyone relying on precision from that source is a gambler.
Richard
I know for a fact you get a lot of pulses and such in industrial apps where, for instance, a megawatt motor (about 1200 horsepower) turns on, it can make power spikes in the line that can effect other users a mile away or more. But that does not effect the overall accuracy of the sine wave power, instead putting out some kind of voltage spike that lasts for a brief time, say 1/10th of a second (just sticking out a number).
Since you get in the US 60 cycles per second and in the UK 50, then in 1/10th of a second 6 cycles can go by or 5 in the UK. So for that time period the sine wave regularity is interrupted and you maybe lose 5 or 6 cycles of continuity. But since the waves are very well synced when the sine wave is reinstated the phase of the wave has not been lost.
That kind of thing does not happen on such a large scale in home use, someone turns on a microwave and some smaller pulses can get into the house wiring but not at a level that would effect an old fashioned electric clock.
BTW, computer power supplies don't have to have extreme precision in converting from ac to dc. If so those UPS systems (uninterruptable power supplies) would make a computer go bonkers because it puts out a wave closer to a square wave than the nice regular sine wave coming in from the mains.
That does not present that much of a problem to computer power supplies which are designed to filter out nasty square wave components of a sine wave but I know also for a fact (having seen the outcome) of some of the cheapo power strip surge protectors when presented with power from these UPS supplies, they tend to blow up.
That is because in a capacitor, for instance, if it is designed to suppress ripple at 100 or 120 hertz, all is well when it is given voltage from a nice sine wave mains supply but with a UPS, the output is anything but sine like, lots of high frequency components are now presented in the current coming out of the UPS.
The problem there is the capacitor allows higher frequency components of the wave to pass right through since capacitors tend to block DC but pass higher frequencies. So cheapo surge protectors typically have a combination of toroid coils, capacitors and MOV (Metal Oxide Varistors, which which shunts high voltage spikes to ground). The capacitors however, just pass higher frequency components of the power spike right on through.
If an audio mixer for instance, is designed to have a nice low noise DC supply at 50 Hz, when used at 60 Hz, will have somewhat more hum than it had when plugged into a 50 Hz mains supply. The slightly (about 10 Percent) higher frequency means that much more ripple protection will be needed at 60 hertz.
I know older reel to reel tape decks designed to run at 50 Hz, taken to the US and run there on 60 Hz, runs about 10 percent faster, a 15 IPS deck would run about 17 IPS in the US. They used motors designed to be directly driven by AC and intimately responded to the mains frequency.
Newer recorders went to DC motors which get timing accuracy from quartz synced supplies.
I would seem (IMHO) that it would mainly be an issue that relates to Synchronous motors, its been a long time since basic eletro-tech for me, so I did a quick bit of research.
Quote from wikipedia
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Uses of Synchronous motors
find applications in all industrial applications where constant speed is necessary.
Improving the power factor as synchronous condensers.
Low power applications include positioning machines, where high precision is required, and robot actuators.
Mains synchronous motors are used for electric clocks.
Record player turntables
AdvantagesSynchronous motors have the following advantages over non-synchronous motors:
Speed is independent of the load, provided an adequate field current is applied.
Accurate control in speed and position using open loop controls, eg. stepper motors.
They will hold their position when a DC current is applied to both the stator and the rotor windings.
Their power factor can be adjusted to unity by using a proper field current relative to the load. Also, a "capacitive" power factor, (current phase leads voltage phase), can be obtained by increasing this current slightly, which can help achieve a better power factor correction for the whole installation.
Their construction allows for increased electrical efficiency when a low speed is required (as in ball mills and similar apparatus).
They run either at the synchronous speed or they do not run at all.
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So I was quite amazed to see that a really heavy industrial application like a ball mill could be using a synchronus motor, not sure how much variation in frequency will affect something like that? Maybe it will drop the efficiency very slightly thru some kind of dV/dt loss?
Anyway very intresting thread
Originally posted by watchingall64It could but we looked at just how much change we are talking about, frequency wise, and it looks like less than one part in several thousand so we would be talking about going from say 60 Hz to 59.99 Hz or 60.01 Hz, something like that so a process that requires a 2000 RPM motor would go all the way down to 1998 rpm, and when a ball mill or some torque heavy process starts up and you introduce process material, synchronous or no, the rpm's will go down a lot more than the numbers I just made up, at least for a brief period of time.
I would seem (IMHO) that it would mainly be an issue that relates to Synchronous motors, its been a long time since basic eletro-tech for me, so I did a quick bit of research.
Quote from wikipedia
*****************
Uses of Synchronous motors
find applications in all industrial applications where constant speed is necessary.
Improving the pow ...[text shortened]... op the efficiency very slightly thru some kind of dV/dt loss?
Anyway very intresting thread
I know the rpm drops a bit on the Banbury rubber mixer I used to work on, where the 2000 hp motor running at 216 rpm and geared down to 16 rpm at the actual grinding faces, when 500 pounds of rubber hits the metal, there is a huge increase in the megawatt power reading and a small reduction in the rpms till the rubber heats up and gets more taffy like. It comes out so hot it has to be rolled out and a long line of water spray to cool off the rubber before it gets to the tire presses.
So in that case the change in rpm's is not critical.