240 volts

On Wed, 27 Feb 2008 19:06:14 -0600 Ben Miller wrote: | snipped-for-privacy@ipal.net 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.

Reply to
phil-news-nospam
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Option 1: Fire the purchasing manager who changed my spec and bought something that I specified to work on a voltage I know I have in the plant.

Option 2: if it's just a motor, get it rewound for 208 3 Phase, replace control transformers, replace fuses, replace (adjust) overload heaters, quick check that the panel wiring is heavy enough. I assume we're talking a few hundred kVA here, not something passing thousands of amps.

Option 3: Autotransformer, or if it really needs the isolation, transformer.

Option 4: Build a methane cracker connected to the natural gas supply, use the hydrogen made to run a fuel cell stack producing 400 V DC, then devise a 12-pulse near-sine-wave variable frequency inverter (and birdbath) to power said machine.

These are the solutions that I've used. OK, not the last one, but I once ran a TV set on a variable-frequency drive.

Bill

Reply to
Bill Shymanski

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snipped-for-privacy@ipal.net

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It would have to be sized and configured for each real world aplication. In my case 208 is actully 201 most days at most of the locations I have to deal with.

Reply to
Tim Perry

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.

Reply to
VWWall

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.
Reply to
VWWall

Every TV broadcast sync generator I've used had a 4X burst crystal. (14.31818 MHz for the US NTSC system.)

Reply to
Michael A. Terrell

On Wed, 27 Feb 2008 19:10:43 -0600 Ben Miller wrote: | snipped-for-privacy@ipal.net wrote: |> On 27 Feb 2008 19:19:50 GMT snipped-for-privacy@ipal.net 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.

Reply to
phil-news-nospam

| snipped-for-privacy@ipal.net 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.

Reply to
phil-news-nospam

According to Phil, that should be 14.31818182 MHz. :-)

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.

Reply to
VWWall

On Wed, 27 Feb 2008 18:21:54 -0800 VWWall wrote: | 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.

Reply to
phil-news-nospam

Many frequency standards are now derived from GPS signals. Of course these are synchronized to atomic standards. It's easier than having your own atomic clock.

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.

P.S.: Have you got your FCC Registration Number? It's needed for license renewals and general access to the FCC site.

Reply to
VWWall

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

Reply to
Dave Martindale

| 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 :-)

Reply to
phil-news-nospam

On Wed, 27 Feb 2008 21:06:18 -0800 VWWall wrote: | Michael A. Terrell wrote: |> VWWall wrote: |>> snipped-for-privacy@ipal.net 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.

Reply to
phil-news-nospam

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

Reply to
Stuart

Oops, yes, you're right I was thinking

136. * sqrt(3) = 236.

Yep, my bad.

120 * sqrt(3) = 210 120. * sqrt(3) = 209.

Point is, no matter how well you know the precision of one factor (sqrt(3)), if the other factor is only known to two or three significant digits, any product of the two can really only be known to two or three significant digits.

And if you only measure the initial 120 volts to the nearest ten volts, I agree. And that's pretty much my point. If you measure it to the nearest volt, (120. with the decimal point), then you can tell the difference.

But with all your 'refinements', you're still starting from '5 MHz'. And just how accurate is the 5 MHz crystal considering the ambient temperature of the crystal is pretty much uncontrolled? At the broadcast studio, I'm sure their's are more precise. But the one in the TV set? If I'm not mistaken, that's why they use a PLL circuit.

You've assumed the '5 MHz' is exact, and therefore the 3.58 MHz is wrong.

Why couldn't it have been.....

5,000,634.92063 Hz * 63/88 = 3,580,000 Hz

(see, you're not the only one with an arbitrary precision calculator :-)

You're not trying to blow smoke and claim that the color burst frequency in an old TV is derived from multiplying 5,000,000.000 Hz times exactly 63/88 ??? Like to see the analog circuit that produces such exact multiplication. Sure wasn't in my old RCA set that I tore into a couple of times :-)

Yes I do quite a bit of programming thank you very much. Since most floating point numbers are already an inexact representation of 'real' numbers, they can be inherently flawed (hint, use 'doubles', there are more significant digits). Yes, you point out correctly (as anyone who has studied "Numerical Methods" can tell you) that when adding floating point values of widely different decades, the exact order of operations can have an effect on the exact outcome. In general, the more floating operations you go through, the fewer and fewer significant digits you can rely on.

That's why there are BCD and 'arbitrary precision' techniques.

By the way, if you use something other than base 10 for your fractional representation (or base 2 as used in IEEE-754 floating point format), you can represent some numbers more precisely.

But again, you can take as much precision of a mathematically defined value as you want. When you multiply / divide it into something that is measured to only two significant digits and try to claim the result is 207.8461 and is 'more accurate' than 208, you've wasted a lot of everyone's time.

To claim....

120 * sqrt(3) = 207.8461

Is pure nonsense. You cannot possibly improve upon the accuracy of the original measurement. Yet that is what this sort of statement is claiming. "I measured the voltage to the nearest ten volts (120), and thus I know the accuracy of the line-line wye voltage to the nearest ten-thousandth of a volt (207.8461)."

Now, if you had said....

120 * sqrt(3) = 207.8461 plus or minus 17.3205

I would agree with that. And everyone would see that the 'answer' is not that well known (could range from about 190 to 220). But look at what all your 'accuracy' has accomplished.

I see this a lot when doing unit conversions as well. If you go to a definitive source for the conversion from one set of units to another, you'll find that some conversion factors are given as *exact*, while others are approximations to some number of significant digits. For example, an inch is defined by NIST as *exactly* 25.4 mm. So a foot is *exactly* 304.8 mm or 0.3048 m. But 1 meter is only *approximately 3.28083989501 feet.

daestrom

Reply to
daestrom

In many engineering fields (outside of electronics), it's also easy to use the wrong engineering units. Or use the inverse of the conversion from one to another. ;-)

Some 'units-phobics' proclaim how metric is so much easier than our (the US) units of measurements. But in actuality, it's just that you can still get the right answer a lot of times because the conversion factors are often just 1. For example, Push with a force of 12 Newtons for a distance of 30 meters over a period of 10 seconds. How many Watts? Play around for a minute or so and you can come up with 12*30/10 = 36. But in actuality, one is converting Newton-meters to Joules (1) and Joules/sec to Watts (1).

12 Newtons * 30 meters / 10 seconds * [(1 Joule) / (1 Newton-meter)] * [(1 Watt-second) / (1 Joule)] = 36 Watt

This is all to often forgotten in the simplicity of just ignoring the conversion factors (because they're always '1').

In US units, if the problem is 'Push with a force of 12 lbf for a distance of 30 feet over a period of 10 seconds, how many horsepower?', you have to actually understand the system of units, and how to apply them.

12 lbf * 30 feet / 10 seconds * [(1 hp) / (550 ft-lbf/s)] = 0.065 horsepower

In a way, our system of units, because it is so bizarre, helps teach us to follow through with the units and understand the relationship between force, distance, time and power.

(note: I did *not* say 0.065455 horsepower :-)

daestrom

Reply to
daestrom

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.

I got cheated! Mine has two leading zeros; it has only 8 digits of precision. :-(

Reply to
VWWall

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.

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.

It might be useful to do some calculations using both methods, but stray TV set radiation numbers is probably hard to come by!

Reply to
VWWall

On Thu, 28 Feb 2008 17:01:01 -0800 VWWall wrote: | snipped-for-privacy@ipal.net wrote: |> On Wed, 27 Feb 2008 21:26:35 -0800 VWWall 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.

Reply to
phil-news-nospam

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