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240 volts

Discussion in 'Electrical Engineering' started by [email protected], Feb 26, 2008.

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  1. Guest

    You have a machine that requires 240 volt three phase power. It requires
    connection to 3 phase lines and ground, but not neutral. You ask your
    utility to supply 240 volt delta and they say no. The machine fails to
    operate on 208 volts. What do you do? How many different solutions could
    you think of to explore?
     
  2. Palindrome

    Palindrome Guest

    Get an appropriate star<> delta transformer, perhaps?

    Move to a country where the distribution companies are actually helpful?

    Connect the supply that you *do* have to the heater on a *large*
    jacuzzi, ideally overlooking a large beautiful mountain range. The
    jacuzzi to have a wine cooler and suitable quantities of a fine wine or
    two. Chill the parts that benefit from chilling. Warm the parts that
    don't. Life really is too short...
     
  3. Palindrome

    Palindrome Guest

    I've just finished making myself a 5kW TIG inverter - standard
    components that cost me <100GBP. I can carry it with one hand..

    My old, less powerful one, has WHEELS.

    Now, if someone could do the same thing for an Argon cylinder.. ;)
     
  4. Guest

    | On 26 Feb 2008 19:20:30 GMT, wrote:
    |
    |>You have a machine that requires 240 volt three phase power. It requires
    |>connection to 3 phase lines and ground, but not neutral. You ask your
    |>utility to supply 240 volt delta and they say no. The machine fails to
    |>operate on 208 volts. What do you do? How many different solutions could
    |>you think of to explore?
    |
    | Is this a residential application?

    It's three phase. I didn't mention country. But in the USA, three phase
    power to residential users is rare. But I'm not really asking about the
    type of service, just how to get a picky 240 volt machine to work.


    | Obvious but not yet mentioned are autotransformers on each 208 volt
    | phase. Also, the utility will probably supply 480 volt delta and you
    | can use a 480-240 volt transformer. Choice of solution would depend on
    | other 3 phase equipment that might require Y, delta at different
    | voltages and the magnitudes of these loads.

    They might supply 480Y/277, too.

    At least one utility I found would provide 240Y/139 in certain locations.
    I don't know how they accomplish that. Maybe they found some transformers
    they can get the 138.564 volts out of, or approximate it some other way.
    But I do know utilities prefer not to have delta secondary services these
    days, presumably due to phase feedback situations and blowing lots of MV
    fuses.


    | I'd put the phase converter at the bottom of the list no matter what
    | its initial cost advantage over a transformer.

    I didn't think of that. But I don't think I would consider it, either.


    | But you know all of this so what's up?

    I'm just checking to see all the creative solutions. Personally, if I
    were faced with this, I'd take the 208Y/120 and add the autotransformer
    in boost configuration to get closer to that 240 volt need.

    Although 208 volts might not work on some 240 volt machines, hopefully
    just a few volts away would achieve that. Boosting each 120 volt leg
    to 136 volts with a 120->16 volt transformer would give you 235.5589
    volts line-to-line. That might be enough. But if one really needs to
    get closer, there are other configurations. The closest one I figured
    out would get 239.7 Y / 138.4 volts. It would use a 240->24 volt
    transformer with primary connected C-A and secondary wired in series
    from A, giving a "bent" leg. The primary would have 208 volts at a 30
    degree phase angle relative to the N-A leg, giving a boost of 20.8 volts
    at the same angle. That would give 138.4 volts with a sum angle of 4.3
    degrees for a L-L voltage of 239.7. There are configurations for more
    than 240 volts, as well.

    Another option is a 208/120 to Scott-T.
     
  5. Guest

    | In article <>,
    | wrote:
    |
    |> You have a machine that requires 240 volt three phase power. It requires
    |> connection to 3 phase lines and ground, but not neutral. You ask your
    |> utility to supply 240 volt delta and they say no. The machine fails to
    |> operate on 208 volts. What do you do? How many different solutions could
    |> you think of to explore?
    |
    | Do your own homework.

    I already did. I'm just checking to see if I missed any creative ideas and
    to see what kind of diversity others as a group would have.
     
  6. Guest

    |
    | |> On Wed, 27 Feb 2008 00:53:02 GMT Salmon Egg <>
    | wrote:
    |> | In article <>,
    |> | wrote:
    |> |
    |> |> You have a machine that requires 240 volt three phase power. It
    | requires
    |> |> connection to 3 phase lines and ground, but not neutral. You ask your
    |> |> utility to supply 240 volt delta and they say no. The machine fails to
    |> |> operate on 208 volts. What do you do? How many different solutions
    | could
    |> |> you think of to explore?
    |> |
    |> | Do your own homework.
    |>
    |> I already did. I'm just checking to see if I missed any creative ideas
    | and
    |> to see what kind of diversity others as a group would have.
    |>
    |> --
    |>
    | |---------------------------------------/----------------------------------|
    |> | Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below
    | |
    |> | first name lower case at ipal.net /
    | |
    |>
    | |------------------------------------/-------------------------------------|
    |
    |
    | I actually have this issue Phil. I used a buck boost transformer. This is a
    | light and intermittent load. A bank of relays at the end of a long cable
    | run.

    I'm curious what the configuration is. I have a list of many different
    configurations near to, and far from, 240 volts, than can be derived from
    208Y/120.
     
  7. Beachcomber

    Beachcomber Guest

    Phil, why do you use terms like 235.5589 volts? No electrical
    engineers do that. It is improper usage and unprofessional to imply
    precision to 4 decimal places for common electrical circuits.

    You have some unique and original ideas, but it almost seems that you
    are off in a different electrical world somewhere, with your own
    standards and conventions.
     
  8. Guest

    |
    |>Although 208 volts might not work on some 240 volt machines, hopefully
    |>just a few volts away would achieve that. Boosting each 120 volt leg
    |>to 136 volts with a 120->16 volt transformer would give you 235.5589
    |>volts line-to-line. That might be enough. But if one really needs to
    |>get closer, there are other configurations.
    |
    | Phil, why do you use terms like 235.5589 volts? No electrical
    | engineers do that. It is improper usage and unprofessional to imply
    | precision to 4 decimal places for common electrical circuits.

    The precision _IS_ there ... because the number is the result of an
    arithmetic calculation using a high level of precision with a formula
    I believe to be accurate. This is very different than if I were to
    physically measure the voltage of a circuit with a voltmeter that has
    4 digits of accuracy and precision. In the latter case you would see
    me write "235.6" or whatever it happens to be.

    It is an accuracy vs. precision issue. Accuracy is needed in order to
    correctly reflect the mathematical formula used. In the event some other
    formula results in a value somewhere near there, that would when rounded
    in the practical manner yield the very same result, the accuracy value
    is what will distinguish the different formulas. Precision is then how
    the value is expressed to carry the accuracy (of the calculation).

    Although in this case I do not know of another formula that could give
    a result close enough to, when rounded, appear to be the same, I cannot
    rule out some formula existing. In the past I have run into cases where
    entirely different formulas ... formulas that are not mathematically the
    same (e.g. one cannot be transformed into the other), give results that
    are closer to each other than the practical precision normally used.

    So ... as a standard practice, when numbers are produced as a result of
    doing mathematical/arithmetic calculations, I use enough precision to
    give a very high level of confidence in matching the correct formula.
    Sometimes I express a precision as extreme as arithmetic being performed
    can do. Sometimes I reduce it some for convenience, but leave enough to
    be sure there is likely no ambiguity as to which formula is used.

    Someone wishing to review my calculations can then match the numbers very
    closely to be sure that not only am I using the correct formula, but am
    also using valid trigonmetry implementations (e.g. code I did not write).

    If I measure a voltage with a voltmeter, I will express it as precisely
    as the device is capable of accurately measuring and precisely displaying.
    If it has an accuracy of 1/10 of a volt in a 200 volt range (rather good)
    I'll use that and might state the voltage as "119.1" or "121.0". But if
    it only has an accuracy of 1 volt, I'll state it as "119" or "121".

    So when you see me use a highly precise expression like "235.5589", it is
    coming from a mathematical calculation done with at least 6 or 7 digits
    of precision (probably more since I default to using the double type which
    has 14 or so digots), using a formula I believe to be accurate.

    If I ever manage to make a real physical measurement with such accuracy,
    I'll be sure to let you know about that miracle device capable of doing
    such a thing.


    | You have some unique and original ideas, but it almost seems that you
    | are off in a different electrical world somewhere, with your own
    | standards and conventions.

    Like doing mathematical formula based programming to automatically explore
    lots of models?

    Here is the output of one of my programs that explores a variety of ways
    to configure different buck-boost transformers, including 480/240/120 volt
    transformers, and running transformers at much lower than design voltage
    just as a means to get a desired ratio (e.g. 208 volts being fed to a
    transformer designed step 480 volts down to 120 just because that is the
    only common transformer to get a 4:1 ratio).

    The first 2 mumeric colums give the resultant system (at calculation level
    precision slightly reduced to fit the output format). The 4th and 5th give
    the voltage being added to 120 volts, and the phase angle of that added
    voltage vector. The 6th gives the buck-boost transformer primary voltage,
    and the 7th and 8th describe the buck-boost transformer being used.

    Notice the two "103.923048" volt results. They are really the same thing
    in a geometric/vector sense, even if the configuration to arrive at them
    are different. The precision of the expression reveals that.

    Notice the rows with "228.630707" and "228.945408". Those are _different_
    kinds of configurations that are _not_ the same as vector math goes. The
    fact that the numbers are different reveals this. If these had been
    rounded, that fact would be hidden. If you measured them with a typical
    voltmeter, you wouldn't know as both might read "229".

    There are other examples of close numbers in this list.

    103.923048 Y / 60.000000 : 120.000 + 60.000 @ 180 (120.000 via 240 -> 120)
    103.923048 Y / 60.000000 : 120.000 + 103.923 @ 150 (207.846 via 240 -> 120)
    137.477271 Y / 79.372539 : 120.000 + 51.962 @ 150 (207.846 via 480 -> 120)
    152.420471 Y / 88.000000 : 120.000 + 32.000 @ 180 (120.000 via 120 -> 32)
    166.276878 Y / 96.000000 : 120.000 + 24.000 @ 180 (120.000 via 120 -> 24)
    168.000000 Y / 96.994845 : 120.000 + 27.713 @ 150 (207.846 via 240 -> 32)
    177.583783 Y / 102.528045 : 120.000 + 20.785 @ 150 (207.846 via 240 -> 24)
    180.000000 Y / 103.923048 : 120.000 + 60.000 @ 120 (120.000 via 240 -> 120)
    180.133284 Y / 104.000000 : 120.000 + 16.000 @ 180 (120.000 via 120 -> 16)
    181.865335 Y / 105.000000 : 120.000 + 15.000 @ 180 (120.000 via 120 -> 15)
    183.597386 Y / 106.000000 : 120.000 + 14.000 @ 180 (120.000 via 120 -> 14)
    185.329436 Y / 107.000000 : 120.000 + 13.000 @ 180 (120.000 via 120 -> 13)
    186.418883 Y / 107.628992 : 120.000 + 32.000 @ 120 (120.000 via 120 -> 32)
    187.061487 Y / 108.000000 : 120.000 + 12.000 @ 180 (120.000 via 120 -> 12)
    187.445992 Y / 108.221994 : 120.000 + 13.856 @ 150 (207.846 via 240 -> 16)
    190.494094 Y / 109.981817 : 120.000 + 24.000 @ 120 (120.000 via 120 -> 24)
    192.468179 Y / 111.121555 : 120.000 + 10.392 @ 150 (207.846 via 240 -> 12)
    193.989690 Y / 112.000000 : 120.000 + 8.000 @ 180 (120.000 via 240 -> 16)
    195.468668 Y / 112.853888 : 120.000 + 16.000 @ 120 (120.000 via 120 -> 16)
    196.150452 Y / 113.247517 : 120.000 + 15.000 @ 120 (120.000 via 120 -> 15)
    196.845117 Y / 113.648581 : 120.000 + 14.000 @ 120 (120.000 via 120 -> 14)
    197.453792 Y / 114.000000 : 120.000 + 6.000 @ 180 (120.000 via 240 -> 12)
    197.552525 Y / 114.057003 : 120.000 + 13.000 @ 120 (120.000 via 120 -> 13)
    198.272540 Y / 114.472704 : 120.000 + 12.000 @ 120 (120.000 via 120 -> 12)
    201.275930 Y / 116.206712 : 120.000 + 8.000 @ 120 (120.000 via 240 -> 16)
    202.849698 Y / 117.115328 : 120.000 + 6.000 @ 120 (120.000 via 240 -> 12)
    208.624064 Y / 120.449159 : 120.000 + 10.392 @ 90 (207.846 via 240 -> 12)
    209.227149 Y / 120.797351 : 120.000 + 13.856 @ 90 (207.846 via 240 -> 16)
    210.940750 Y / 121.786699 : 120.000 + 20.785 @ 90 (207.846 via 240 -> 24)
    213.232268 Y / 123.109707 : 120.000 + 6.000 @ 60 (120.000 via 240 -> 12)
    213.316666 Y / 123.158435 : 120.000 + 27.713 @ 90 (207.846 via 240 -> 32)
    215.109275 Y / 124.193398 : 120.000 + 8.000 @ 60 (120.000 via 240 -> 16)
    218.238402 Y / 126.000000 : 120.000 + 6.000 @ 0 (120.000 via 240 -> 12)
    218.979451 Y / 126.427845 : 120.000 + 12.000 @ 60 (120.000 via 120 -> 12)
    219.970453 Y / 127.000000 : 120.000 + 13.000 @ 60 (120.000 via 120 -> 13)
    220.970586 Y / 127.577427 : 120.000 + 14.000 @ 60 (120.000 via 120 -> 14)
    221.702503 Y / 128.000000 : 120.000 + 8.000 @ 0 (120.000 via 240 -> 16)
    221.979729 Y / 128.160056 : 120.000 + 15.000 @ 60 (120.000 via 120 -> 15)
    222.997758 Y / 128.747816 : 120.000 + 16.000 @ 60 (120.000 via 120 -> 16)
    223.615742 Y / 129.104609 : 120.000 + 10.392 @ 30 (207.846 via 240 -> 12)
    226.495033 Y / 130.766968 : 120.000 + 51.962 @ 90 (207.846 via 480 -> 120)
    228.630707 Y / 132.000000 : 120.000 + 12.000 @ 0 (120.000 via 120 -> 12)
    228.945408 Y / 132.181693 : 120.000 + 13.856 @ 30 (207.846 via 240 -> 16)
    230.362757 Y / 133.000000 : 120.000 + 13.000 @ 0 (120.000 via 120 -> 13)
    231.447618 Y / 133.626345 : 120.000 + 24.000 @ 60 (120.000 via 120 -> 24)
    232.094808 Y / 134.000000 : 120.000 + 14.000 @ 0 (120.000 via 120 -> 14)
    233.826859 Y / 135.000000 : 120.000 + 15.000 @ 0 (120.000 via 120 -> 15)
    235.558910 Y / 136.000000 : 120.000 + 16.000 @ 0 (120.000 via 120 -> 16)
    239.699812 Y / 138.390751 : 120.000 + 20.785 @ 30 (207.846 via 240 -> 24)
    240.399667 Y / 138.794813 : 120.000 + 32.000 @ 60 (120.000 via 120 -> 32)
    249.415316 Y / 144.000000 : 120.000 + 24.000 @ 0 (120.000 via 120 -> 24)
    250.567356 Y / 144.665131 : 120.000 + 27.713 @ 30 (207.846 via 240 -> 32)
    263.271723 Y / 152.000000 : 120.000 + 32.000 @ 0 (120.000 via 120 -> 32)
    274.954542 Y / 158.745079 : 120.000 + 60.000 @ 60 (120.000 via 240 -> 120)
    274.954542 Y / 158.745079 : 120.000 + 103.923 @ 90 (207.846 via 240 -> 120)
    289.309523 Y / 167.032931 : 120.000 + 51.962 @ 30 (207.846 via 480 -> 120)
    311.769145 Y / 180.000000 : 120.000 + 60.000 @ 0 (120.000 via 240 -> 120)
    374.699880 Y / 216.333077 : 120.000 + 103.923 @ 30 (207.846 via 240 -> 120)
     
  9. Guest

    On 27 Feb 2008 19:19:50 GMT wrote:

    | 219.970453 Y / 127.000000 : 120.000 + 13.000 @ 60 (120.000 via 120 -> 13)

    I didn't even notice this one before. But I checked. It is correct that
    a vector of exact whole number length 120 at 0 degrees plus a vector of
    exact whole number length 13 at 60 degrees (1/6 of the arc of a circle)
    yields a sum vector that is an exact whole number length 127 (though at
    an angle I am unable to find a rational relationship to PI for). While
    it is possible to have triangles at any whole number lengths you pick, as
    long as no side is equal to or greater than the sum of the other sides,
    perhaps it is interesting when some can be formed with at least some
    corners having a rational relation to PI (e.g. 1/6 of a full circle).

    And I would not have noticed it had I rounded all the numbers to whole.

    OK, so I like precision in calculations, like the square root of 3 is:
    1.7320508075688772935274463415058723669428052538103806280558069794519330169088

    But some people seem to prefer whole numbers. So for them I have:
    13005325352767864879663023255649031427 / 7508628093319191445537920541850040962
     
  10. Guest

    On Wed, 27 Feb 2008 17:32:09 -0500 wrote:

    | These digital volt meters may have 4 digits of "precision" but nobody
    | says they have that degree of "accuracy". Most will give you an
    | inaccurate answer precise out to 4 decimal places unless you just got
    | them back from the calibration lab and you haven't done anything to
    | change the calibration (dropped it, had a static discharge while you
    | were using it, left in in a hot car or whatever)

    Suppose you know that there is a 95% probability that the meter will be
    off by plus or minus 1 volt. You get a reading of 121.3 volts. What is
    the probability that the real voltage is 120.1 volts? Which of these is
    a more correct sattement:

    1. 95% probability the voltage is between 120.3 and 122.3
    2. 95% probability the voltage is between 120 and 122

    The interplay of accuracy and precision can be an interesting one. For more
    information, see: http://en.wikipedia.org/wiki/Accuracy_and_precision
    That is, if you have more than a 50% trust in the accuracy and precision of
    Wikipedia :)
     
  11. Guest

    |
    | |> |
    |> |>Although 208 volts might not work on some 240 volt machines, hopefully
    |> |>just a few volts away would achieve that. Boosting each 120 volt leg
    |> |>to 136 volts with a 120->16 volt transformer would give you 235.5589
    |> |>volts line-to-line. That might be enough. But if one really needs to
    |> |>get closer, there are other configurations.
    |> |
    |> | Phil, why do you use terms like 235.5589 volts? No electrical
    |> | engineers do that. It is improper usage and unprofessional to imply
    |> | precision to 4 decimal places for common electrical circuits.
    |>
    |> The precision _IS_ there ... because the number is the result of an
    |> arithmetic calculation using a high level of precision with a formula
    |> I believe to be accurate. This is very different than if I were to
    |> physically measure the voltage of a circuit with a voltmeter that has
    |> 4 digits of accuracy and precision. In the latter case you would see
    |> me write "235.6" or whatever it happens to be.
    |>
    |
    | Just to be pendantic, just because the sqrt(3) can be known to a high degree
    | of precision, you're multiplying a number that has as many significant
    | digits as you could want, with a number that is stated to only have three
    | significant digits (120. with the decimal is three sig. digits, 120 without
    | the decimal is only two significant digits). Mathematical purists will tell
    | you that any multiplication or division can only be carried out to the same
    | number of significant digits as the least significant term. So...
    |
    | 120. * sqrt(3) = 236. (three significant digits in 120.)

    I get something closer to 207.84609690826527522329356098070468403313663 :)

    If I use 1.732 I get 207.84
    If I use 1.73 I get 207.6
    If I use 1.7 I get 204
    If I use 2 I get 240

    I have no idea where the 236 came from. Did you mean to start with 208
    and just copied the number I was using before?


    | 120 * sqrt(3) = 240 (only two significant digits in 120)

    That's as bad as sqrt(3) = 2.


    | And backing up a bit further, when you add you have to be even more careful
    | about precision.
    |
    | 120. + 16. = 136. (because 120. (with the decimal point) is three
    | significant digits.)

    In the three phase wye buck-boost example, I consider the 136 to be
    accurate and precise because the transformer can have an exact 15:2
    winding ratio to derive 16 volts from 120 volts.


    | But ...
    |
    | 120 + 16 = 140 (because the '16' has to be shifted to at least the same
    | decade as the least significant digit of 120 and that means you round it off
    | to...
    | 120 + 20 = 140

    You won't be able top tell the difference between using a 16 volt boost
    transformer and a 24 volt boost transformer, if you express the result
    as 140 volts.


    | Most of us skimp on the rules a bit, but taking a number like 120 * sqrt(3)
    | and claiming the answer to seven significant digits is over the top.

    It depends on the context. If I am doing a calculation that _should_
    come up with the same value as 120 volts times the square root of three,
    but want to just express the result value to let someone else match it,
    I will use more digits. Usually 6 is enough to not just identify the
    system, but identify that the calculation did more than just get into
    the right ball park.


    | daestrom
    | I told you I was going to be pendantic .... :)

    I consider myself to be pedantic. My practice is that if there is a known
    statistical error in the values I'm calculating with, I let those errors
    work their way through in the appropriate way. I do NOT increase those
    error artificially. So if I am working with 120 volts plus or minus 10
    volts (at 95% confidence), then in three phase wye, the line to line value
    is 207.846096908265275 volts plus or minus 17.3205080756887729 volts (at
    95% confidence). THEN I round that result down to 208 volts plus or minus
    17 volts, and let the confidence figure get a little fuzzy.

    I would disagree with your "mathematical purist" (mentioned way above)
    because I feel that is being quit UNpure to allow TWO sources of error
    to operate in a formula when only one value (the measurement) has error
    and the other (the mathematically defined square root of three) has no
    error.

    How much I round depends on the context. If I'm talking about a type of
    electrical system, I'll say something like 208Y/120 or 220Y/127 as the
    case may be. Accuracy is not important there as it is just identification,
    not a measurement or calculation (which can be an identification of the
    formula used).

    Back when I was in junior high school, without the aid of any calculator
    or computer, I pondered the meaning of the frequency 3.58 MHz as it related
    to the TV broadcast standards (which at the time I "knew" to be 15,750 Hz
    horizontal and 60 Hz vertical. But I found a book in the school library
    that gave the value as 3.579545 MHz. Just that much information allowed
    me to "reverse engineer" this number to determine it came from 5 MHz times
    63 divided by 88, and really had "454545" repeated (3579545.45[45..] Hz),
    and that the horizontal frequency was really 15734.265734[265734..] Hz,
    and that the vertical frequency was really 59.940059[940059..] Hz. All
    that semantic understanding came out of just getting 4 more digits of
    precision. Over a decade later I found that the FCC broadcast rules
    actully defined the value the same way, as 5 MHz times 63/88. It is still
    identifiable as 3.58 MHz. But if I want to compare it to something else
    semantically, I need a much more precise value. Would you recognize it
    as the NTSC color subcarrier frequency if I called it 3.6 MHz? or 4 MHz?

    Now along comes the new ATSC standard. Yes, I have very precise values
    for it. What is _really_ scary about the exact DEFINED bits per second
    rate it has is that the fractional part (in either MHz or Hz) in decimal
    repeats only after 312 digits! But it is a lot easier to express it as
    its exactly defined value in the form of 867996/44759 Mbps. Work out
    that division on a calculation with thousands or more digits precision
    adn you will get the repeat every 312 digits. Fortunately I only need
    to express 11 digits to nail the value dead on.

    How many digits of precision is needed from a calculation that _should_
    give a result of exactly 1 do you need to see as a value just shy of 1
    (e.g. 0.999....) to know that it _should_ be exactly one as opposed to
    merely being _nearly_ 1? Does 0.999 do it? Does 0.999999 do it? How
    about 0.999999999999999999999999999999999999999999999999? I would never
    say 0.9 is 1. But as the number of 9's continues, the confidence that
    the valus really should have been exactly 1 increases rapidly.

    Do you do any computer programming? If so, do you just add up a long
    list of floating point values in the order given, or do you sort them
    so you accumulate the sum by adding the lowest values first?

    How many digits do you want for the square root of three expressed as a
    ratio of two integers with a precision in digits equal to or greater than
    the SUM of the digits in the numerating AND denominator?

    Anyone can just say:
    17320508075688772935274463415058723669428052538103806280558069794519330169088
    divided by:
    10000000000000000000000000000000000000000000000000000000000000000000000000000
    but that is only 77 digits of precision for 154 digits expressed.

    But if I give you:
    81637354237035839875406774706916734691676867556988461166524491402570869800626
    divided by
    47133348444681477624409145446409554706879415291771528507046516487702731598175
    then you can be sure you have 154 digits of precision. Try it.

    Remember 355/113 for the value of PI? I have way better fractions. You
    won't _need_ them, of course. But I have them.
     
  12. Guest

    | wrote:
    |> If I measure a voltage with a voltmeter, I will express it as
    |> precisely
    |> as the device is capable of accurately measuring and precisely
    |> displaying. If it has an accuracy of 1/10 of a volt in a 200 volt
    |> range (rather good) I'll use that and might state the voltage as
    |> "119.1" or "121.0". But if
    |
    | Many mid to high end multimeters are more accurate than that.

    I'm happy with a 4 digit voltmeter. But I want 1 Hz tuning steps on
    my SSB ham rig, even to the high end of the UHF band.


    |> it only has an accuracy of 1 volt, I'll state it as "119" or "121".
    |>
    |> So when you see me use a highly precise expression like "235.5589",
    |> it is coming from a mathematical calculation done with at least 6 or
    |> 7 digits
    |> of precision (probably more since I default to using the double type
    |> which has 14 or so digots), using a formula I believe to be accurate.
    |>
    |> If I ever manage to make a real physical measurement with such
    |> accuracy, I'll be sure to let you know about that miracle device
    |> capable of doing such a thing.
    |>
    |
    | You are only talking about 1ppm or 0.1ppm. A lot of equipment exists with
    | that accuracy. I have calibration instruments in my lab that will do it.
    | However, that is several orders of magnitude better than any field
    | measurements that I make. Even if you did make measurements with that
    | accuracy on an electrical power system , it would be meaningless from a
    | practical standpoint. It would be difficult to measure the difference in
    | winding temperatures, for example, with a voltage variation of 0.0001%.

    If you measure the voltage and find it is 278.415 volts, it could be just
    a bit different in a few seconds. At this level of accuracy and precision
    we're into line noise levels :) But, my mathematical model calculations
    don't have line noise to worry about (unless I am doing noise modeling).


    | You are presenting a great mental excercize, but if you need to go that far
    | down to differentiate between the results of two formulas, then as a
    | practical matter in most power work, they are the same.

    I want to be able to recognize them in the mathematical model sense, too.
     
  13. Guest

    | wrote:
    |> On 27 Feb 2008 19:19:50 GMT wrote:
    |
    |> OK, so I like precision in calculations, like the square root of 3 is:
    |> 1.7320508075688772935274463415058723669428052538103806280558069794519330169088
    |>
    |> But some people seem to prefer whole numbers. So for them I have:
    |> 13005325352767864879663023255649031427 /
    |> 7508628093319191445537920541850040962
    |
    | Great theory, but you will get plenty close using 1.732 for almost any power
    | calculation.

    I know I will. But the purpose for using more precision is different than
    merely getting close.
     
  14. Guest

    | wrote:
    |
    |> Back when I was in junior high school, without the aid of any calculator
    |> or computer, I pondered the meaning of the frequency 3.58 MHz as it related
    |> to the TV broadcast standards (which at the time I "knew" to be 15,750 Hz
    |> horizontal and 60 Hz vertical. But I found a book in the school library
    |> that gave the value as 3.579545 MHz. Just that much information allowed
    |> me to "reverse engineer" this number to determine it came from 5 MHz times
    |> 63 divided by 88, and really had "454545" repeated (3579545.45[45..] Hz),
    |> and that the horizontal frequency was really 15734.265734[265734..] Hz,
    |> and that the vertical frequency was really 59.940059[940059..] Hz. All
    |> that semantic understanding came out of just getting 4 more digits of
    |> precision. Over a decade later I found that the FCC broadcast rules
    |> actully defined the value the same way, as 5 MHz times 63/88. It is still
    |> identifiable as 3.58 MHz. But if I want to compare it to something else
    |> semantically, I need a much more precise value. Would you recognize it
    |> as the NTSC color subcarrier frequency if I called it 3.6 MHz? or 4 MHz?
    |
    | If you do a bit more reading, you'll find it's never exactly 5,000,000 *
    | 63/88, but is whatever the phase lock loop in the receiver set it to.

    What the carrier frequency _actually_ is and what the _definition_ is are
    two different things. The FCC allows (or at least used to) a tolerance
    of plus/minus 10 Hz. Broadcasters generally get a LOT closer than that
    with atomic clock oscillators. They are as pedantic as I am, it seems :)
    But there are good reasons, too.


    | This is determined by the color burst sent by the transmitter, which is
    | nominally derived from a 3.58 MHz xtal. It's still NTSC, (never the
    | same color), in spite of the inaccuracy of the frequency.

    The receiver locks to the received signal subcarrier frequency. Using a
    crystal to do that keeps it nice and stable during the lock. But even if
    the crystal is tuned off a little, it will still lock and still be stable.
    So the accuracy of the receiver subcarrier oscillator is the same as the
    transmitter. And in the case of network affiliate broadcasters, that is
    likely locked on to the network much of the day, and certainly during
    network air time.

    This will be moot for full power broadcasters in less than a year.
     
  15. Guest

    | daestrom wrote:
    |
    |> Most of us skimp on the rules a bit, but taking a number like 120 *
    |> sqrt(3) and claiming the answer to seven significant digits is over the
    |> top.
    |>
    |> daestrom
    |> I told you I was going to be pendantic .... :)
    |
    | I took the P.E. exam before there were hand calculators, so we all used
    | slide rules. One advantage was they were perfectly suited for
    | engineering work without ever needing to be pedantic. ;-)
    |
    | I've seen more measurements screwed up by lack of knowledge than by
    | insufficient number of decimal places.

    Using the wrong formula can do that.
     
  16. It's also easy to get two sine waves with exactly 90 degrees of phase
    shift between them (as required for the two colour subcarriers for I/Q
    or U/V colour modulation) if you start with a clock at 4X the final
    frequency, have two divide by 4 circuits, and have the two dividers one
    state out of sync.

    Dave
     
  17. Guest

    | I once saw a proposal to determine the listeners to each TV channel by
    | using a mobile van with a narrow band receiver tuned to the horizontal
    | frequency radiated by each active TV receiver. By comparing the
    | frequency/phase and the arrival azimuth of the intercepted signal, one
    | could determine to which station each set was tuned. It got a poor
    | reception, (sic), from the broadcasters who wanted to know more
    | demographics than just the time/location of the receivers.

    I thought it would be easier to do the color subcarrier. But maybe this
    proposal was before color?


    |> This will be moot for full power broadcasters in less than a year.
    |
    | P.S.: Have you got your FCC Registration Number? It's needed for
    | license renewals and general access to the FCC site.

    Yes, I have an FRN. It has 10 digits of precision :)
     
  18. Guest

    | Michael A. Terrell wrote:
    |> VWWall wrote:
    |>> wrote:
    |>>
    |>>> Back when I was in junior high school, without the aid of any calculator
    |>>> or computer, I pondered the meaning of the frequency 3.58 MHz as it related
    |>>> to the TV broadcast standards (which at the time I "knew" to be 15,750 Hz
    |>>> horizontal and 60 Hz vertical. But I found a book in the school library
    |>>> that gave the value as 3.579545 MHz. Just that much information allowed
    |>>> me to "reverse engineer" this number to determine it came from 5 MHz times
    |>>> 63 divided by 88, and really had "454545" repeated (3579545.45[45..] Hz),
    |>>> and that the horizontal frequency was really 15734.265734[265734..] Hz,
    |>>> and that the vertical frequency was really 59.940059[940059..] Hz. All
    |>>> that semantic understanding came out of just getting 4 more digits of
    |>>> precision. Over a decade later I found that the FCC broadcast rules
    |>>> actully defined the value the same way, as 5 MHz times 63/88. It is still
    |>>> identifiable as 3.58 MHz. But if I want to compare it to something else
    |>>> semantically, I need a much more precise value. Would you recognize it
    |>>> as the NTSC color subcarrier frequency if I called it 3.6 MHz? or 4 MHz?
    |>> If you do a bit more reading, you'll find it's never exactly 5,000,000 *
    |>> 63/88, but is whatever the phase lock loop in the receiver set it to.
    |>> This is determined by the color burst sent by the transmitter, which is
    |>> nominally derived from a 3.58 MHz xtal. It's still NTSC, (never the
    |>> same color), in spite of the inaccuracy of the frequency.
    |>
    |>
    |> Every TV broadcast sync generator I've used had a 4X burst crystal.
    |> (14.31818 MHz for the US NTSC system.)
    |
    | According to Phil, that should be 14.31818182 MHz. :)

    14.31818181818181818181818181818181818181818181818181818181818181818181818...

    or 5000000*63/22


    | You're correct. For practical circuits, the higher frequency xtal has a
    | better form factor and can be more easily "pulled" to exact frequency.
    | I believe it's easier to get an AT, (flat temperature), cut at that
    | frequency.

    That and easier to derive quadrature phases.
     
  19. Guest

    | wrote:
    |>
    |> | I once saw a proposal to determine the listeners to each TV channel by
    |> | using a mobile van with a narrow band receiver tuned to the horizontal
    |> | frequency radiated by each active TV receiver. By comparing the
    |> | frequency/phase and the arrival azimuth of the intercepted signal, one
    |> | could determine to which station each set was tuned. It got a poor
    |> | reception, (sic), from the broadcasters who wanted to know more
    |> | demographics than just the time/location of the receivers.
    |>
    |> I thought it would be easier to do the color subcarrier. But maybe this
    |> proposal was before color?
    |
    | The point is the horizontal deflection is applied at a high level to
    | relatively unshielded coils on the CRT. Although this falls off rather
    | rapidly, it's still large enough for a narrow band receiver to detect at
    | a distance.
    |
    |> | P.S.: Have you got your FCC Registration Number? It's needed for
    |> | license renewals and general access to the FCC site.
    |>
    |> Yes, I have an FRN. It has 10 digits of precision :)
    |
    | I got cheated! Mine has two leading zeros; it has only 8 digits of
    | precision. :-(

    I counted the leading 0 digits because of the nature of a finite format
    index number that it is. Just because the assignments are sequential
    does not mean any are more or less precise than any other. But if you
    really feel that the leading 0 digits do not count toward precision,
    then I guess you can feel good about having gotten 8 digits of precision
    as under that concept, I got only 7.
     
  20. Guest

    | Stuart wrote:
    |> In article <>,
    |>
    |>> I once saw a proposal to determine the listeners to each TV channel by
    |>> using a mobile van with a narrow band receiver tuned to the horizontal
    |>> frequency radiated by each active TV receiver. By comparing the
    |>> frequency/phase and the arrival azimuth of the intercepted signal, one
    |>> could determine to which station each set was tuned. It got a poor
    |>> reception, (sic), from the broadcasters who wanted to know more
    |>> demographics than just the time/location of the receivers.
    |>
    |> Funny, I thought the usual system was to pick up stray radiation from the
    |> IF oscillator. You know exactly what channel the set's tuned to that way
    |
    | I assume you mean the local oscillator. This can vary considerably from
    | set to set, depending on where the actual IF is, requiring a relatively
    | wide-band receiver. It's radiation is also required to be below
    | specified limits to comply with FCC regulations.

    Virtually all TVs were made with the same IF frequency. The FCC channel
    allocations were made with this in mind to avoid channels bleeding in as
    images on the other side of the LO.


    | The horizontal frequency is within a few cycles. Off-the-air "samples"
    | of all the local TV transmitters can be used to compare. Also, a loop
    | antenna will give a precise azimuth as well as considerable gain.

    Early in TV broadcasting, that might have worked, with each station being
    a little different in frequency. Now days, they are all locked tight to
    very good references.
     
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