Temperature Conversion
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Decibel is a fucking ridiculous scale. It's dimensionless (since it's a ratio between two quantities), but whenever somebody uses dB's, they implicitly associate it with some special snowflake reference point because it'd otherwise be largely useless (OK, sometimes something is appended to the dB part that kinda identifies the reference, but far from always). It's logarithmic -we have scientific notation for something, guys- and I still have PTSD from having to sketch by hand a circuit's gain in dB over the frequency domain in the basic electronics courses and then pretend that my measured squiggly line obviously was a series of linear bits.
Filed under: 100dB = 10^10 times something
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@cvi Probably it proliferates because just measuring the intensity of the source in watts gives numbers which can easily vary 10 orders of magnitude. And non-scientists don't understand scientific notation.
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@PleegWat said in Temperature Conversion:
non-scientists don't understand scientific notation.
The other night I was playing one of those idle-ish type flash games which, presumably through using default representations, gave big numbers as "2.12e11" (maybe a plus after the "e"). Down in the comments I saw someone complaining about all the mental maths they have to do to work out how big the numbers are. I'm thinking, "literally just look at the bit on the end in 90% of cases"
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@PleegWat said in Temperature Conversion:
And non-scientists don't understand scientific notation.
Problem: Identified.
@kazitor said in Temperature Conversion:
"2.12e11"
ITYM 113.26dBbs.
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@cvi said in Temperature Conversion:
Decibel is a fucking ridiculous scale.
Yes. Bel would be better since then you'd be able to take the number and just use it as an exponent (with 10 as the base value and some application-specific value as the mantissa) to get the real physical quantity. Except noooo… we gotta multiply it by 10 just so that morons get a scale with an extra digit before the decimal point.
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@dkf decibel is like PHP - solving imaginary problems of imaginary beginners, which ends up causing major headache for people who actually use it for their work.
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@dkf said in Temperature Conversion:
the “deci” in “decibel” means tenths (of a bel)
As opposed to "deca" which means tens, and is probably the rarest of the small SI prefixes.
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@PleegWat decagram is pretty common in parts of Europe.
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@PleegWat said in Temperature Conversion:
As opposed to "deca" which means tens, and is probably the rarest of the small SI prefixes.
Except for capacitance, of course. Almost every office has some form or another of decaf.
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@PleegWat said in Temperature Conversion:
@dkf said in Temperature Conversion:
the “deci” in “decibel” means tenths (of a bel)
As opposed to "deca" which means tens, and is probably the rarest of the small SI prefixes.
Fairly common way to measure thlons though.
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- Decibel are sometimes (eg. power) 10 Log X/A, sometimes (eg. voltage) 20 Log X/A, which makes them even more confusing.
- dBs are always used in some snowflake manner (dBwtf is 20 Log X/A, where A, the reference, is 1V fed into a 500ohm load on a summer Sunday morning in a mountain chalet)
- When referring to volume, units are or should be generally dB<some letter>SPL, where the letter states the weighting used and SPL reminds you that it's a sound pressure level unit.
- Here in Italy we call kelvins "gradi kelvin". Anyway, when units take the name of some person they have a capitalised symbol but lower-case long name (in fact, decibels are dB, newtons are N, volts are V).
- It's more appropriate to say that °C and K have the same scaling but a different starting point.
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@admiral_p said in Temperature Conversion:
When referring to volume, units are or should be generally dB<some letter>SPL, where the letter states the weighting used and SPL reminds you that it's a sound pressure level unit.
Until the last four words, I was under impression you're talking about physical volume.
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@admiral_p In French, "degrés Kelvin" is an error; the correct form is "kelvins" when the zero is absolute. Of course, kelvins are only used in science, while degrees Celsius are used for everyday applications (weather, cooking, air conditioning, etc.).
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@remi said in Temperature Conversion:
@PleegWat said in Temperature Conversion:
As opposed to "deca" which means tens, and is probably the rarest of the small SI prefixes.
Except for capacitance, of course. Almost every office has some form or another of decaf.
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@Khudzlin said in Temperature Conversion:
@admiral_p In French, "degrés Kelvin" is an error; the correct form is "kelvins" when the zero is absolute. Of course, kelvins are only used in science, while degrees Celsius are used for everyday applications (weather, cooking, air conditioning, etc.).
I suspect it is in Italian too (I checked, it actually is). But usage is widespread also in schools.
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By the way, the world of electronics (especially audio) is full of ridiculously confusing units.
For example, you have
- W RMS
- W AES
- program watts
- peak watts
- "musical" watts (I dunno if these are or were widespread outside Italy)
- W PMPO
- volume units (VU) and their companion, dBVU
- loudness units full scale (LUFS)
- dBFS "digital" full scale
- dBu
- dBm
It's infuriating.
(The only watts for rating equipment power that you need to know are AES watts - determined destructively - coupled certainly with %THD - and even here, what's the point of measuring %THD at 1kHz? The assumption is that power amps are more or less linear and flat through audio, but it is only an assumption - with maybe crest factor to know how much headroom you really have).
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@admiral_p Almost all engineering domains are full of stupid units (borne out of usage).
From the world of petroleum engineering, I present to you the "formation volume factor". Fairly straightforward in definition, it's the ratio between the volume occupied by gas at underground reservoir condition and the volume occupied by the same gas at surface condition (basically, by how much gas will expand as it goes up from the reservoir to the surface). Obviously quite useful when dimensioning production installation etc.
It's a ratio of volumes, so it's unitless, right? RIGHT? Uh-uh...
well-known standard forms
[equation, with baked-in conversion factors and unit at the end] RB/scf
where rcf/scf = reservoir cubic feet per standard cubic feet, RB = reservoir barrels [...]
The three forms in Eq. 2 are for specific units. In the first two equation forms, the pressure is in psia and the temperature is in °R.Reservoir barrels per standard cubic feet, computed from a pressure in psi and a temperature in degrees rankine. Yep, that's a thing.
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@cvi said in Temperature Conversion:
@remi said in Temperature Conversion:
decaf
ffffffffff
It looks like you fell asleep there from a lack of caffeine. Do you want me to undo that for you?
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@remi said in Temperature Conversion:
degrees rankine
Brought to you by the "who needs Mars rovers, anyway" department.
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@topspin I even spent some time checking if I should write "degrees rankine" or "rankine" or "Rankine", in light of the 'ing going on
in this threadhere...
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@remi said in Temperature Conversion:
@topspin I even spent some time checking if I should write "degrees rankine" or "rankine" or "Rankine", in light of the 'ing going on
in this threadhere...This thread just made me go ?? over this parametric selection box for FET current-rating range:
N-FETs can be specified by their current rating, e.g. 3A.
P-FETs work backwards to N-FETs. So, the equivalent P-FET would be specified as -3A.
Both the hypothetical FETs here would be carrying 3A absolute, so really that box is backwards with its 'min' and 'max' when selecting P-FETs...
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@remi said in Temperature Conversion:
Reservoir barrels per standard cubic feet, computed from a pressure in psi and a temperature in degrees rankine. Yep, that's a thing.
Why do I suddenly get the feeling that I’ve just read about something dreamed up by Americans … ?
My pet peeve is kilowatt-hours. Why isn’t this simply expressed in (mega)joules?
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@Gurth said in Temperature Conversion:
My pet peeve is kilowatt-hours. Why isn’t this simply expressed in (mega)joules?
My pet peeve is kilowatt-hours when used as a unit of power, rather than energy. I've never been able to figure out what people mean when they use that.
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@PleegWat said in Temperature Conversion:
@Gurth said in Temperature Conversion:
My pet peeve is kilowatt-hours. Why isn’t this simply expressed in (mega)joules?
My pet peeve is kilowatt-hours when used as a unit of power, rather than energy. I've never been able to figure out what people mean when they use that.
They mean that they don't know what's going on. That they're uneducated.
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@Benjamin-Hall It's like those people who say "If you weigh 60 kilograms on Earth you'd weigh only 10 kilograms on the moon". It makes no sense because kilograms are a unit of mass, not force.
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@Gurth said in Temperature Conversion:
My pet peeve is kilowatt-hours. Why isn’t this simply expressed in (mega)joules?
Because that's actually quite useful. You have a 500 watt device which runs for two hours? Voilà, you just consumed 1 kWh of electrical energy and will have to pay 0.25€ for it.
It's the same reason why we're using liters and not m³ for denotating volumes of liquids. It's simply grounded in everyday units. And with liters you at least don't have this 3.6Ewhatever conversion factor mucking things up needlessly.
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@Rhywden A kilowatthour is 3.6 megajoules. A cubic meter is 1000 liters. My water and gas meters are read in cubic meters with 3 extra digits which I don't need to provide.
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@PleegWat said in Temperature Conversion:
@Rhywden A kilowatthour is 3.6 megajoules. A cubic meter is 1000 liters. My water and gas meters are read in cubic meters with 3 extra digits which I don't need to provide.
Yes, and how often do you use 0.0005 m³ of milk when cooking? Not to mention that it's a mouthful when speaking about it.
"Now, mom, carefully pour 0.0001 cubic meters ... yes, that's 0.1 cubic decameters, ..."
I mean, hell, even scientists use convenience units. Just look at
eV
(electronVolts). And I know for a fact that some Theoretical Physicists regularly setc = 1
because writing2.99792458E8 m/s
gets annoying after a while.
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@Gurth said in Temperature Conversion:
My pet peeve is kilowatt-hours. Why isn’t this simply expressed in (mega)joules?
For the same reason why it's liters per 100km and not square nanometers.
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@PleegWat said in Temperature Conversion:
@Benjamin-Hall It's like those people who say "If you weigh 60 kilograms on Earth you'd weigh only 10 kilograms on the moon". It makes no sense because kilograms are a unit of mass, not force.
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Personally, I prefer all my units to be derived from cubic parsecs, and to hell with everyone else.
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@mott555 parsecs are so arbitrary. Planck units FTW!
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@mott555 The distance at which the maximum parallax as the earth moves around the sun is one arc second, cubed?
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@Rhywden said in Temperature Conversion:
And I know for a fact that some Theoretical Physicists regularly set
c = 1
because writing2.99792458E8 m/s
gets annoying after a while.my favorite units set c, electron charge, h-bar, and the mass of an electron all to 1.
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@mott555 said in Temperature Conversion:
Personally, I prefer all my units to be derived from cubic parsecs, and to hell with everyone else.
But how do you derive anything involving mass, time, current, luminance or temperature?
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@kazitor said in Temperature Conversion:
@mott555 said in Temperature Conversion:
Personally, I prefer all my units to be derived from cubic parsecs, and to hell with everyone else.
But how do you derive anything involving mass, time, current, luminance or temperature?
I'll give it a try, just for kicks.
Mass: Derived by the amount of Einsteinium contained in a cubic parsec.
Time: Simple. The base unit is how long it takes a photon to traverse one edge of a cubic parsec.
Current: Imagine a cubic parsec packed so tightly with electrons that electron degeneracy pressure prevents it from being any denser. But let's also pretend gravity doesn't exist so it doesn't turn into a black hole and inconvenience us. The number of electrons in that region becomes the base unit of charge, and so current is the number of those passing past a point per unit of time.
Luminance: Based on the brightness of a flame that comes from a wax candle the size of one cubic parsec.
Temperature: Set the zero point at the temperature of a flame that comes from a wax candle the size of one cubic parsec. And the interval of each degree is based on a change in luminance of that candle.
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@mott555 said in Temperature Conversion:
Luminance: Based on the brightness of a flame that comes from a wax candle the size of one cubic parsec.
Alternative suggestion:
Luminance: Based on the brightness of your cubic parsec of electrons meeting a friendly cubic parsec of positrons. Assume they pair up nicely.
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@cvi That might not be the ideal luminance reference. As far as I can find on Google, it luminance is defined in reference to the spectral response of the human eye, (i.e., only includes visible light), but the peak radiance of your proposed reference is going to be somewhere in the gamma range.
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@Benjamin-Hall said in Temperature Conversion:
@PleegWat said in Temperature Conversion:
@Gurth said in Temperature Conversion:
My pet peeve is kilowatt-hours. Why isn’t this simply expressed in (mega)joules?
My pet peeve is kilowatt-hours when used as a unit of power, rather than energy. I've never been able to figure out what people mean when they use that.
They mean that they don't know what's going on. That they're uneducated.
It'd be a terrible, terrible mistake to assume either of the above implies the other, or (shudder) the inverse.
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@Gribnit said in Temperature Conversion:
It'd be a terrible, terrible mistake to assume either of the above implies the other, or (shudder) the inverse.
That's more than the needed amount of usual gribnetese in one sentence.
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@topspin said in Temperature Conversion:
@remi said in Temperature Conversion:
degrees rankine
Brought to you by the "who needs Mars rovers, anyway" department.
Come on, the Rankine scale is awesome for the simple reason that you can legitimately say that it's five hundred degrees outside.
Well, right now it's in the 450's, but come summer it'll be back up there.
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@Groaner said in Temperature Conversion:
you can legitimately say that it's five hundred degrees outside.
Eh. 300 is hot enough.
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@Rhywden said in Temperature Conversion:
0.0001 cubic meters ... yes, that's 0.1 cubic decameters
Typo there.
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@mott555 said in Temperature Conversion:
Luminance: Based on the brightness of a flame that comes from a wax candle the size of one cubic parsec.
Temperature: Set the zero point at the temperature of a flame that comes from a wax candle the size of one cubic parsec. And the interval of each degree is based on a change in luminance of that candle.Scented or unscented?
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@Rhywden said in Temperature Conversion:
Because that's actually quite useful. You have a 500 watt device which runs for two hours? Voilà, you just consumed 1 kWh of electrical energy and will have to pay 0.25€ for it.
Do any consumers make this kind of calculation on a regular basis?
It's the same reason why we're using liters and not m³ for denotating volumes of liquids. It's simply grounded in everyday units.
I don’t think that’s a valid comparison. The litre is technically unnecessary, true, but it has a name of its own like, say, the newton or the volt, not a compound name like kilowatt-hour. Convenience names tend to be there to simplify things — imagine if we expressed volumes of milk in m·m·m — yet kWh does pretty much the opposite.
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@Gurth Clearly the real WTF is hours.
You run a 500-watt device for 8 kiloseconds: 4 megajoules.
(1 ks = 16 min 40 sec, if you haven't memorised that for some reason)