Hi,
It is simple, build it to the simple ratio calculation and measure the speed error.
Then get the same turner to make another pulley with the correction built in.
The error from the mains will swamp the pulley calculation error, but our starter did mention Quartz once so we don't yet know what's in his mind.
And this is "the most daunting" part of the project
It is simple, build it to the simple ratio calculation and measure the speed error.
Then get the same turner to make another pulley with the correction built in.
The error from the mains will swamp the pulley calculation error, but our starter did mention Quartz once so we don't yet know what's in his mind.
And this is "the most daunting" part of the project
AndrewT said:
That is not true.
Mains frequency error merasured as Allen deviation is typically less than 100ppm, reducing to better than 10ppm averaged over the long term (several hours or more).
A standard commercial quartz crystal is about 100ppm but gets worse with ageing.
It is very easy to get the pulley wrong by several percent, as per some of the answers in this thread which were about 5% out (that's 50,000 ppm for the mathematically challenged).
balderdash.Mark Kelly said:
In the UK the frequency can vary by about 1Hz either side of nominal.
Over the long term it is accurate. The power companies use a synchronous clock to attempt to keep the daily variation as close to zero as they can manage economically.
So the minute by minute variation is about +-2% but the daily target variation is about 12ppm (1 second over 24hrs) and even better over 1week/month.
If one cannot measure the time for 100revolutions of the 33.33rpm turntable and compare that to 180 seconds with about 0.5% accuracy then one should not be building a turntable.
If 0.5% accuracy is not close enough then do 500revolutions.
Now do the same experiment in the early hours and compare the results to measurements taken at peak demand (1600hrs to 1800hrs).
is that absolute accuracy or variation?
Brainticket said:
Is this some kind of a 'wind up', the Linn sub platter I've just measured is more like 162mm not 126mm (or did you type it wrong).
Assuming the motor rotates at 300rpm the diameter of the drive pulley will have to be more like 19mm. I don't understand your post - in what way doesn't it make sense with 9? The numbers 7 and 9 relate to the factor by which the drive pulley will have to be smaller than the inner platter and have nothing to do with their specific dimensions. You have to work out the dimensions after you know the relative ratio between the two as you cannot alter either the input speed (300rpm - if this is correct) or the output speed (33.3rpm).
By the way its isn't not "is'nt" and doesn't not "does'nt".
Hi,
Andrew,
You are off by a factor of two when calculating rpm based on the # of poles. It starts with 2 poles, hence the rpm formula for a synchronous motor can be written as:
rpm=120*[frequency]/[# of poles]
ex: a 16 pole synchronous motor should run 375rpm @50Hz and 450rpm @60Hz.
AndrewT said:
Andrew,
You are off by a factor of two when calculating rpm based on the # of poles. It starts with 2 poles, hence the rpm formula for a synchronous motor can be written as:
rpm=120*[frequency]/[# of poles]
ex: a 16 pole synchronous motor should run 375rpm @50Hz and 450rpm @60Hz.
AndrewT said:An Englishman/woman correcting the spelling of another English person is an anachronism.
The English can't spell and they certainly haven't learned to speak good english. Just ask a Scot for an opinion.
You lot can't even spaek with out sounding stupid & that goes for the crap they come out with too that clearly posted right here...I'm just laughing here at the oddd technical mistakes your making.In which other i see are nicely pointing out.You may ask why you! That's because i hate the Scots as much as you do us...
ps:& yes a Linn sub is 162mm nice to see someones awake.
AndrewT said:
As I have never measured the frequency in the UK I can't gainsay that. I must ask, however, how come your power utilities are so inept?
Actual measurements I've made on Australian line frequencies agree with the US measurement made by Leapsecond.com (the source of the figures I quoted). It is my understanding that the requirements of generators as set by IEC 60034-1 are far tighter than the 2% variation you have proposed.
I should refrain from replying when we are so obviously off topic, but a little humour might help while we await Brain's reply.
Anachronism refers to the historical "fact" that some of us have habitually misused "our" language even though we should know better than our foreign language members who often express themselves much more fluently than we can do.
But if you don't agree, I can accept that. We Scots are introverted after all.
Anachronism refers to the historical "fact" that some of us have habitually misused "our" language even though we should know better than our foreign language members who often express themselves much more fluently than we can do.
But if you don't agree, I can accept that. We Scots are introverted after all.
AndrewT said:I should refrain from replying when we are so obviously off topic, but a little humour might help while we await Brain's reply.
Anachronism refers to the historical "fact" that some of us have habitually misused "our" language even though we should know better than our foreign language members who often express themselves much more fluently than we can do.
But if you don't agree, I can accept that. We Scots are introverted after all.
No scence of humour is one of Scot folks traits..
I think nuf said about this topic cos Ameriacan & Australians are involved, wrong frequency will reap technical issues.An Ameriacn magazine reviewing a british turntable, can never sound the same as it does in britain..As the American driven motor will exhibit an higher frequency noise floor than our driven motor of the same.
AndrewT said:
Hmmm .......
The above is simply not true. Huge flywheels are used to store
energy and smooth the power demand but this has nothing to
do with the operating frequency of the generators.
The idea 50hz falls in periods of high demand might make sense
to someone but it is simply not true and there is no "economy".
/sreten.
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