Direct vs. indirect measurements - for AgingYoung and others

[Folly]

This is split from the "Danny Klein - Fuel from Water" thread.

A long discussion started when, in response to a comment that the Sun's temperature could not be measured, followed by a comment that it certainly could, AgingYoung said

Upthread there was a mention of measuring the surface of the sun and it was pointed out that we could measure that temp. We can’t. We can derive or calculate a temperature. It was mentioned that we could move instruments further from the sun (maybe at some distance where they wouldn’t melt) and extrapolate the temperature. That’s a technique of calculating a value and isn’t a direct measurement. There are measured quantities like distance. You can actually take a tape and measure distance. Then there are derived quantities like speed (mph). Then there are calculated quantities like the surface temperature of the sun. It’s probably splitting hairs but these are distinctions made in instrumentation.

A number of other comments followed, like

This might help clarify the point. There are some quantities that are based on standards and you can take an instrument that is calibrated to that standard and directly measure an unknown quantity. Temperature is based on a standard. If you were sick and we wanted to know what your temperature was, I could take a thermometer (calibrated to that standard) and directly measure your temperature.

Frequency is a quantity that is considered derived. A method to calculate frequency is to measure the time between two consecutive occurrences of the event (the period) and then compute the frequency f as the reciprocal of this time..

F=1/t

When you measure temperature using derived measurements you aren't directly measuring; you are calculating it. You can't take a thermometer and directly measure the temperature of the sun. As you know it's too hot.

To the point of what is being sensed and temperature readings: if you are using a thermocouple it's sensing temperature change. You're directly reading temperature. If you're sensing light firstly you're sensing a derived unit (freq) then inferring temperature. You are not directly sensing temperature.

There is indeed a difference. That difference is, 'what is being sensed.' This point is fundamental to the field of instrumentation and process control. Basics in any discipline are established so that people within it can be on the same page when discussing the details. Usually someone not interested or versed in a particular discipline looks at things differently. That's a common occurrence.

and It might be hard to follow but I'll give it one last shot. In a thermister the change in resistance is a function of temperature. The instrument varies as a function of the variable you are sensing. Mercury in a thermometer expands and contracts as a direct function of temperature.

When you're measuring a variable that is a function (i.e. freq) of the actual variable you want to measure (i.e. temp) you aren't directly measuring it. That's the case when first measuring frequency then inferring what temperature is. Temperature isn't the first variable that's causing the change in your instrument; it's not a direct measurement.


A number of people noted that in this sense, all temperature measurements are indirect, and any claim that spectrographic measurements of the temperature are less direct than a meat thermometer are, at best, misguided. After a number of claims that perhaps this is just too complicated for everyone, and this is just the way it is in industry, I posted a small quote from http://www.isa.org/InTechTemplate.cfm?Section=Article_Index1&template=/ContentManagement/ContentDisplay.cfm&ContentID=9464

All temperature measurements are indirect. That is to say, the measurement is the measurement of volumetric expansion (liquid-filled thermometer), dimensional change (bimetallic thermometer), electromotive force (thermocouple), resistance (resistance temperature detector, or RTD), radiated energy (radiation thermometer), or some other characteristic of a material that varies predictably and reproducibly with temperature.


At this point, as expected, AgingYoung leaps on the next paragraph on this page

However, in industrial process measurement and control, the concept of direct and indirect temperature measurement has a different meaning. A direct measurement is a measurement of the temperature of the product itself. An indirect measurement is a measurement of some other temperature from which one can infer the product temperature.

saying it confirms what he has been saying all along, and

I might add that example clarifies direct and indirect measuring of temperature in a process but still the variable being measured is temperature. When we are attempting to know the temperature of the sun we aren't measuring temperature; we're measuring frequency (among other things) and inferring temperature from that. There is a slight distinction between 'indirect' and 'inferred' temperature measurements.


AgingYoung, did you even read the two paragraphs that you and I quoted between the two of us? In the first sense of direct measurement, all temperature measurements are indirect. A mercury thermometer is indirect, as it measuring the thermal expansion of a column of mercury, which is itself influenced by the subject temperature. A spectrographic temperature measurement is indirect because it measures the emitted black body radiation.

In the second sense (the "industry sense") described in the paragraph that you quoted, both instruments could be doing direct or indirect measurements. In fact, in the third and fourth paragraphs of the linked site, they even have examples:

An example of direct temperature measurement occurs when, as in roasting meat or making candy, it is possible to insert a thermometer directly into the product; insertion or immersion thermometers are often used.

One uses an indirect measurement in baking bread because one controls the oven air temperature. It is not practical to insert a thermometer into the bread because the action adversely affects the quality of the bread.


AgingYoung: you first tried blaming SI units, and then you insisted it's due to the differing sense of direct measurement used by industry. Do you still insist that we can not directly measure the temperature of the sun, while we can directly measure the temperature of a cup of coffee?

[stormer]

I read the other thread entirely, and this is what I understand AgingYoung to mean.

....Do you still insist that we can not directly measure the temperature of the sun, while we can directly measure the temperature of a cup of coffee?

If you stick this in your coffee to get the temperature, it is a direct measurement.

http://www.evotech.com.my/pictures/mercury.jpg

If you use this to measure the temperature of your coffee, it is not a direct measurement, but a derived one.

http://www.evotech.com.my/pictures/fluke_ir.jpg

Hahaha!

(Now, I got to ask, why are you all trying to convince AgingYoung otherwise? Don't you all get frustrated by it?)

[Dilb]

(Now, I got to ask, why are you all trying to convince AgingYoung otherwise? Don't you all get frustrated by it?)

It's important to try and answer things properly so that people who genuinely want to learn have the right idea presented.

[stormer]

I have to say I really do admire all of our patience with dealing with something / someone like this.

[Paul C. Anagnostopoulos]

If you stick this in your coffee to get the temperature, it is a direct measurement.
It is? Seems to me it involves the heating of the glass, which then indirectly heats the mercury.

~~ Paul

[ponderingturtle]

It is? Seems to me it involves the heating of the glass, which then indirectly heats the mercury.

~~ Paul

Which expands and you measure the expansion. Not as dirrect as it seems

[stormer]

It is? Seems to me it involves the heating of the glass, which then indirectly heats the mercury.

~~ Paul

Oops, I don't think you should take that one sentence in the post to reply to, but rather read the post as a whole? Maybe even read my other post after that to see the context? :D

[Paul C. Anagnostopoulos]

Oops, I don't think you should take that one sentence in the post to reply to, but rather read the post as a whole?
I read the entire post. Perhaps you mean that the temperature gun is more indirect than the thermometer?


Maybe even read my other post after that to see the context?
This one?

I have to say I really do admire all of our patience with dealing with something / someone like this.

~~ Paul

[stormer]

Hey Paul. The direct measurement or indirect measurement is not a distinction I am trying to make, but rather one AgingYoung was in the Denny Klein - Fuel from Water thread.

You should know, in that thread, you asked that discussion about these things be continued here. I did not want to comment on temperature measurement in that thread.

I was just quite (I can't find the right word, so I'll just stick with...) surprised that that discussion resulted in this thread due only to one poster insisting on his view about the direct and derived measurement.

By AgingYoung's opinion, the thermometer would be a direct measurement of temperature, while the InfraRed non-contact would be a derived measurement of the temperature. I don't agree, and I was amused at that poster's opinion.
Hahaha!
I go on to say that (in not so many words) "I admire the patience of the people who were trying to get the message across to the OP even though the OP was being stubborn and contradictory to their own words about direct temperature measurement and derived temperature measurement". I made a typo there in saying "our" when I wanted "your". My mistake.

Hope this helps clear things up

[joobz]

Why is this an issue? Why does it matter that the calculation of the sun's surface temp be a indirect measure?

AgingYoung mentioned that this is an important issue with process control, which is true. there you need to know the response time of the probe (indirect having slower responses typically) and the offsets they may have (surface jacket temperature as a function of internal tank temperature). These things need to be programmed in and modeled, otherwise you get wrong readings.

BUT, I can only assume that those who did calculations on the sun surface temp took into account enough of the issues to provide a reasonably accurate value. If you have an issue with the calculation or assumptions made in the calculation, than those should be addressed. but to claim that the values can't be (or ever be) trusted because we only use indirect measures is just silly.

[ponderingturtle]

Why is this an issue? Why does it matter that the calculation of the sun's surface temp be a indirect measure?

AgingYoung mentioned that this is an important issue with process control, which is true. there you need to know the response time of the probe (indirect having slower responses typically) and the offsets they may have (surface jacket temperature as a function of internal tank temperature). These things need to be programmed in and modeled, otherwise you get wrong readings.

BUT, I can only assume that those who did calculations on the sun surface temp took into account enough of the issues to provide a reasonably accurate value. If you have an issue with the calculation or assumptions made in the calculation, than those should be addressed. but to claim that the values can't be (or ever be) trusted because we only use indirect measures is just silly.


He was asserting initialy that you can't know the temp of the sun because it was an indirrect measurement. Now we never touched on the accuracy of the measurement, but only about how you are measureing it.

[Paul C. Anagnostopoulos]

Hope this helps clear things up.

It does, thanks. So where is AgingYoung?

~~ Paul

[joobz]

He was asserting initialy that you can't know the temp of the sun because it was an indirrect measurement. Now we never touched on the accuracy of the measurement, but only about how you are measureing it.
I've never looked into how they measured/calculated the sun temperature, but that seems like a splitting hairs.
It's like saying, "We don't know the exact value of Pi"

What would the value be used for? I'm guessing that the indirectly measured temperature is useful enough for most calculations. (as is using pi=3.14) If you need better accuracy, you can use pi=3.14159, but is that the case here?


Like I said, if he feels that the value is wrong for some fundemental reason, then it is a valid point. If he feels the value is wrong simply because it is a "indirect measure", then he's whole point is moot.

[ponderingturtle]

I've never looked into how they measured/calculated the sun temperature, but that seems like a splitting hairs.
It's like saying, "We don't know the exact value of Pi"

What would the value be used for? I'm guessing that the indirectly measured temperature is useful enough for most calculations. (as is using pi=3.14) If you need better accuracy, you can use pi=3.14159, but is that the case here?


Like I said, if he feels that the value is wrong for some fundemental reason, then it is a valid point. If he feels the value is wrong simply because it is a "indirect measure", then he's whole point is moot.

His whole point has always been moot, he just managed to troll it out longer.

[Myriad]

This raises the question, is there any such thing as a truly "direct" measurement? Don't the very concepts of "measurement" and "directness" contradict one another?

Use a ruler to measure the distance between two marks on a wooden board. The scale on the ruler doesn't show the distance between the marks; it shows the distance between the adjacent points on the ruler. Close, but not direct.

Of course, you could use the scale on the ruler to show how far apart two scale marks on the ruler are. But there's no unknown value in that scenario. You're not measuring anything. Similarly, you can define the distance between your two marks on your board as a new unit of displacement measurement, and then measure other things (indirectly) using that unit. But defining the unit, in itself, is not measuring anything.

"Direct" as applied to measurement only works as a relative concept. It's more direct, say, to measure the temperature of the sun from the frequencies of the light of the sun's visible disc than to measure it from the frequencies of the light reflected by the moon.

Respectfully,
Myriad

[Folly]

I was just quite (I can't find the right word, so I'll just stick with...) surprised that that discussion resulted in this thread due only to one poster insisting on his view about the direct and derived measurement.

Well, I'm surprised too: I have no idea why I care. For some reason, this really irritated me, and I didn't want to just let it go, even if it was just a tiny, silly claim mentioned in a larger, sillier claim.


This raises the question, is there any such thing as a truly "direct" measurement? Don't the very concepts of "measurement" and "directness" contradict one another?

Use a ruler to measure the distance between two marks on a wooden board. The scale on the ruler doesn't show the distance between the marks; it shows the distance between the adjacent points on the ruler. Close, but not direct.

I had understood comparison to be all measurement was, and because you're comparing two lengths without intermediaries, this is a direct measurement. That seems slightly vague to me, and if there's a better definition, I'd love to hear it.

Of course, you could use the scale on the ruler to show how far apart two scale marks on the ruler are. But there's no unknown value in that scenario. You're not measuring anything. Similarly, you can define the distance between your two marks on your board as a new unit of displacement measurement, and then measure other things (indirectly) using that unit. But defining the unit, in itself, is not measuring anything.

"Direct" as applied to measurement only works as a relative concept. It's more direct, say, to measure the temperature of the sun from the frequencies of the light of the sun's visible disc than to measure it from the frequencies of the light reflected by the moon.

I had also understood there to also be an actual distinction to be made based on intermediary variables. A ruler makes a direct measurement because it compares a length to a length. A thermometer makes an indirect measurement because it compares a length which changes with temperature. I don't ever deal with this in my job, so I don't know whether this is just the sort of thing you hear in school that is completely ignored in the real world, or whether this distinction is actually considered to be of interest. My guess is that it's only the relative sense that is considered, and only so far as it affects the accuracy of the measurement and the conditions under which it applies. I could certainly be wrong: while I was looking for information on this, a German site with English text popped up describing some temperature measurement device that was explicitly stated to be indirect.

[davefoc]

I think AgingYoung made two errors and for whatever reason decided to push on after he realized that he had made them.

The first was the direct/indirect thing. He initially thought that a measurement technique that involved direct contact was fundamentally different than a measurement technique that involved measurement of electromagnetic radiation because one method measured temperature directly and the other method involved a calculation and assumptions about the relationship between the characteristic actually being measured and temperature.

Many posts were generated that explained that this wasn't the case and that in fact there is no method of directly measuring temperature using the definition that he proposed.

He then went on to his second mistake which was that the distinction he was making was recognized by industry.

At least in the links he posted the recognized meaning of direct and indirect with regard to temperature measurement was not what he had in mind. An indirect temperature measurement is one where the temperature of one thing is inferred by measuring the temperature of something else.

So AgingYoung appears to have been wrong. Having been completely wrong myself a few times I can say that it isn't always the easiest thing to just fess up and move on. Since AgingYoung hasn't shown up in this thread, perhaps he is tacitly acknowledging that he was wrong right now.

[joobz]

I think AgingYoung made two errors and for whatever reason decided to push on after he realized that he had made them.

The first was the direct/indirect thing. He initially thought that a measurement technique that involved direct contact was fundamentally different than a measurement technique that involved measurement of electromagnetic radiation because one method measured temperature directly and the other method involved a calculation and assumptions about the relationship between the characteristic actually being measured and temperature.

Many posts were generated that explained that this wasn't the case and that in fact there is no method of directly measuring temperature using the definition that he proposed.

He then went on to his second mistake which was that the distinction he was making was recognized by industry.

At least in the links he posted the recognized meaning of direct and indirect with regard to temperature measurement was not what he had in mind. An indirect temperature measurement is one where the temperature of one thing is inferred by measuring the temperature of something else.

So AgingYoung appears to have been wrong. Having been completely wrong myself a few times I can say that it isn't always the easiest thing to just fess up and move on. Since AgingYoung hasn't shown up in this thread, perhaps he is tacitly acknowledging that he was wrong right now.
that is most likely a fair assessment.

I will state though that people generally gain much more of my respect when they acknowledge fault or being wrong.

I had tried to start a thread where people would post hypotheses they've made in research that turned out to be strikingly wrong, but that failed completely.

It is hard to admit mistakes.

[Iamme]

It is hard to admit mistakes.

Yes. But especially so if you hardly ever make one.

[Schneibster]

I feel comfortable maintaining that ALL measurements of any kind whatsoever are indirect. My rationale is that we cannot experience reality itself directly, but do so only through the signals delivered to our brains by our nervous system. Thus, no matter what we think we are measuring, what we are actually measuring is the frequency of nerve impulses from some input or other. And that's only if you admit that "you" and "I" actually EXIST.

In the presence of all this philosophical uncertainty, I have to decide at some point that I will accept certain facts as manifestations of some "reality" "out there." Making what I consider to be minimal assumptions, I find that the "accuracy" of "indirect" measurements is as good as anything I can come up with as a means of quantifying phenomena in my environment. Thus, I see in this light little difference between very, very closely estimating the temperature of a cup of coffee by sticking a thermometer in it and very, very closely estimating the temperature of the surface of the Sun using blackbody theory and measurement of its spectral peak.

Sounds like someone trying to obfuscate the issues to me.

[Lynx2174]

Yes. But especially so if you hardly ever make one.

Not if you're usually right because you care about being correct. Or if you're honest.

[joobz]

Not if you're usually right because you care about being correct. Or if you're honest.
Honesty and desire to know the truth tend to go hand in hand.

[AgingYoung]

It does, thanks. So where is AgingYoung?

~~ Paul

I'm right here, Paul. Finally got that spellchecker cleaned up.

Although the point shifted from a direct/indirect measurement of average kinetic energy my point was that temperature wasn't the first quantity measured when we attempt to know what the temperature of the sun is. Measuring light intensity (candela) is not a temperature reading. Temperature is inferred from that. I'm not someone that defines standards for the scientific community nor do I write curricula for instrumentation. I'm only aware of what the standards are.

In the case of a thermometer the glass is part of the instrument that either directly or indirectly equalizes in average kinetic energy to the process and a calibrated scale is read to measure the temperature.

I hope this clears things up but call me psychic, I really doubt it will.

Gene

[AgingYoung]

joobz,

Are you suggesting the emboldened part of your quote was a point I made? If that's the case could you directly quote where I said this?

If you have an issue with the calculation or assumptions made in the calculation, than those should be addressed. but to claim that the values can't be (or ever be) trusted because we only use indirect measures is just silly.

Gene

[Dave_46]

<snip>
Measuring light intensity (candela) is not a temperature reading. Temperature is inferred from that. <snip>

Isn't it the frequency of the light that is measured to infer temperature, rather than intensity, or have I got it wrong?

Dave

[joobz]

joobz,

Are you suggesting the emboldened part of your quote was a point I made? If that's the case could you directly quote where I said this?



Gene

I had no idea what you said. I was addressing the questions in this thread. I didn't know how indirect/direct measurements came up in the other thread and was only guessing as to why it would be discussed.

The question I would have is -Why did you bring up the issue with direct vs. indirect measurements?

[AgingYoung]

Dave_46,

Frequencey is a factor, yes.

The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 × 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.

Gene

[AgingYoung]

joobz,

ic, it was ponderingturtle that attributed this blarney to me...
He was asserting initialy that you can't know the temp of the sun because it was an indirrect measurement.
That's a crock; I never made that point.

Gene

[joobz]

joobz,

ic, it was ponderingturtle that attributed this blarney to me...

That's a crock; I never made that point.

Gene
If that's the case, then we have no problem with each other.:D :p:D

[Dilb]

Dave_46,

Frequencey is a factor, yes.



Gene

No.

First, that's the definition of the candela. It measures intensity weighted by a factor to account for human eyesight, in order to rate the brightness of lightbulbs (mostly, anyway). This would be more obvious if you quoted the relevant part of the definition of a candela (and it would be nice if you mentioned it when you copied from wikipedia).

The intensity of light is measured in watts per square metre. By measuring the relative intensities at different wavelengths the temperature can be calculated from the formula for blackbody radiation. There are a number of ways to do so, you could look at the peak frequency, you could compare the relative change in two particular frequencies, or you can measure all the frequencies you can and curve fit to find the best temperature.

You can even skip measuring frequencies and just measure the radiated power, and find out the temperature, although for that to work you need to know the emissivity and the distance from an object, and it really simplifies things if the object is either small or spherical. By amazing coincidence, it works quite well for the sun if you can measure the intensity in space.

[AgingYoung]

... This would be more obvious if you quoted the relevant part of the definition of a candela (and it would be nice if you mentioned it when you copied from wikipedia)...

The tags [ wiki ] ... [ /wiki ] are pretty cool and when I quote from there I use them. I ripped that definition from


http://www.electro-optical.com/whitepapers/candela.htm


Perhaps my confusion of thinking frequency was a factor in determining candela was that the definition DIRECTLY MENTIONED FREQUENCY!!!!! Silly me.

For what it's worth those dolts here....

http://physics.nist.gov/cuu/Units/current.html


have the same misconception. Won't they every learn?

Gene

[Dilb]

Perhaps my confusion of thinking frequency was a factor in determining candela was that the definition DIRECTLY MENTIONED FREQUENCY!!!!! Silly me.
Gene

Sigh.

Candelas do depend on frequency. Candelas are not used to calculated the temperature of an object based on blackbody radiation. The frequency dependance of a candela is in no way related to the frequency dependance seen in blackbody radiation.

[AgingYoung]

Candelas are not used to calculated the temperature of an object based on blackbody radiation..

I do agree this is true and I spoke too fast. I was slightly misled by laziness and the fact that this point was incidental to my real point. I recall studying reactance and rf, etc. in school but I'm pretty sure we didn't consider spectroscopy in much detail if at all.

Gene

eta: Although freq isn't a factor in determining candelas, it is by definition radiation at specific freq. and of certain intensity.

[Dilb]

I do agree this is true and I spoke too fast. I was slightly misled by laziness and the fact that this point was incidental to my real point. I recall studying reactance and rf, etc. in school but I'm pretty sure we didn't consider spectroscopy in much detail if at all.

Gene

eta: Although freq isn't a factor in determining candelas, it is by definition radiation at specific freq. and of certain intensity.

Frequency is a factor in determining candelas. It's an entirely different factor than the one that comes up in blackbody radiation, which was my point. It's not at all incidental. If you read (and understood) any of the sources you quote you'd understand why using a candela when talking about blackbody radiation makes no sense.

[AgingYoung]

Frequency is a factor in determining candelas.

I'd have to see the formula but as I read it freq is a consideration yet not a factor. For instance in inductive reactance...

X=2pi(f)l

Frequency is indeed a factor.

If you read (and understood) any of the sources you quote you'd understand why using a candela when talking about blackbody radiation makes no sense.
I've already mentioned that I spoke too fast. Considering you know I cited


Our patented alexandrite effect spectropyrometer measure high to ultrahigh temperature measurement from 1000 K up to 100,000 K. The spectropyrometer measures the relative spectral power distribution of a radiating body in the UV-VIS-IR wavelength range, integrates the relative spectral power distribution in the whole wavelength range, and determines the temperature using the patented method. The spectropyrometer can measure any type of radiating bodies: blackbody, graybody, plasma, electric arc, etc.

that should be obvious.


Gene

[Dilb]

I'd have to see the formula but as I read it freq is a consideration yet not a factor. For instance in inductive reactance...

X=2pi(f)l

Frequency is indeed a factor.

Gene

What on earth do you think a "consideration but not a factor" is?

The factor can clearly be seen in the graph here (http://www.electro-optical.com/whitepapers/candela.htm). They don't give the formula because it's a messy empirical approximation to human eyesight.

A candela is a measure of luminous intensity, or the "brightness" that a person will rate a beam of light as. For an actual spectral intensity, in W/m2, say 10 W/m2 a yellow beam light will appear the brightest, and other colours appear less bright. You multiply the actual spectral intenisty by the factor given on that page, the luminosity function, and that gives you the brightness in candelas. Hopefully a blue lightbulb of 1 candela will look as bright as a yellow lightbulb of 1 candela, although the blue one will actually be emitting considerably more power.

All of this is entirely unrelated to blackbody radiation. Here the spectral intensity of a frequency changes with temperature, in a way totally unrelated to candelas. I don't see how copying the description of a spectrometer shows that you understand this at all.

[AgingYoung]

2. Mathematics. one of two or more numbers, algebraic expressions, or the like, that when multiplied together produce a given product; a divisor: 6 and 3 are factors of 18.

or in the example I gave inductive reactance is the product of various factors, one of them being frequency.

All of this is entirely unrelated to blackbody radiation.
I've agreed with this twice yet since you keep bringing it up...

The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation(Radiation taken over a sufficiently small spectral interval that the radiance is invariant with wavelength.) of frequency 540 × 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.

As far as I can tell candela is radiation over a specific spectral interval yet doesn't have as it's factor frequency.

I do further agree that average kinetic energy (temperature) isn't the quantity being measured when we infer the sun's temperature. Inference isn't the direct route to arrive at an answer; it's a round about or indirect method.

Gene

[Dilb]

As far as I can tell candela is radiation over a specific spectral interval yet doesn't have as it's factor frequency.

Gene

Try and read the links you cite from, and please try and figure out what that V-lambda Curve thing is. If you don't understand how a factor could be given as a graph, brush up on your pre-calculus.

[AgingYoung]

As you've repeatedly pointed out and as I've repeatedly acknowledged candela isn't germane to the point. Of course you'd have to integrate wattage over that small spectral interval. The fact of the matter is you're quibbling over minor details. At times your opinions have been less than accurate. It's the human condition. For what it's worth I'd probably never agree with you, even if you called me handsome. It is a fact I'm handsome but if you stated it as fact I'd most likely deny it.

Gene

[Folly]

but to claim that the values can't be (or ever be) trusted because we only use indirect measures is just silly.

joobz,

Are you suggesting the emboldened part of your quote was a point I made? If that's the case could you directly quote where I said this?


No, AgingYoung, you didn't say exactly that. You said something even stranger: you said we can't measure the temperature of the Sun. As quoted in the OP: Upthread there was a mention of measuring the surface of the sun and it was pointed out that we could measure that temp. We can’t. We can derive or calculate a temperature. It was mentioned that we could move instruments further from the sun (maybe at some distance where they wouldn’t melt) and extrapolate the temperature. That’s a technique of calculating a value and isn’t a direct measurement. There are measured quantities like distance. You can actually take a tape and measure distance. Then there are derived quantities like speed (mph). Then there are calculated quantities like the surface temperature of the sun. It’s probably splitting hairs but these are distinctions made in instrumentation.This is also where not being a "direct measurement" was brought up.

You have been mentioning translations from temperature to frequency, and people tried to point out that both a mercury thermometer and a spectrographic thermometer are indirect in this sense, noting for example that a mercury thermometer is read by checking a length. After more and more examples (and a really odd sidetrack into SI units) you fell back more and more on the "well that's how it is in industry" line, so I linked to a page from an industrial organisation dealing with instrumentation, systems and process control, one that explicitly states that all temperature measurements are indirect in this sense.

You then happily point to the second paragraph where it actually talks about a differing definition of a direct measurement, saying it confirms what you have been saying all along. You even quote this second paragraph, but not the examples.
All temperature measurements are indirect. That is to say, the measurement is the measurement of volumetric expansion (liquid-filled thermometer), dimensional change (bimetallic thermometer), electromotive force (thermocouple), resistance (resistance temperature detector, or RTD), radiated energy (radiation thermometer), or some other characteristic of a material that varies predictably and reproducibly with temperature.

However, in industrial process measurement and control, the concept of direct and indirect temperature measurement has a different meaning. A direct measurement is a measurement of the temperature of the product itself. An indirect measurement is a measurement of some other temperature from which one can infer the product temperature.

An example of direct temperature measurement occurs when, as in roasting meat or making candy, it is possible to insert a thermometer directly into the product; insertion or immersion thermometers are often used.

One uses an indirect measurement in baking bread because one controls the oven air temperature. It is not practical to insert a thermometer into the bread because the action adversely affects the quality of the bread.

If you re-read the second paragraph and look at the examples, it should be clear that a similar direct/indirect distinction (in the process control sense) in the case of measuring the temperature of the sun would be something like a)measuring the temperature of the sun and b)measuring the temperature of surrounding gas and inferring the temperature of the sun from that. By looking at the intensity and distance, or the emitted spectrum we can do option a. Look at http://www.astronomynotes.com/starsun/s2.htm for an explanation. You can also play around with http://marzipan.atmos.washington.edu/ion_script/ATMS558/main_blackbody.html
which will let you generate blackbody radiation curves plotted against the observed spectrum from the Sun.

Again, note that this measurement is indirect in the non process control sense, as are all temperature measurements, whether based on thermal expansion or blackbody radiation (if you're Schneibster, all measurements are indirect, and I'm not sure I disagree, or at leastI agree that it's a silly, fuzzy distinction.) It's direct in the process control sense, for the limited sense that makes, given it is not an industrial process, because the temperature of the Sun is being measured, not some other related temperature.

If you still disagree, and insist that there is yet another well known (?!) distinction that says we can't measure the surface temperature of the sun, please find some reference explaining this, and then explain why it's more appropriate than either of the other common usages.

[AgingYoung]

It seems what we measure to infer the temperature of the sun is actually power along a spectral interval. That point seems well established. We are indeed not actually measuring the average kinetic energy of the sun (temperature); we infer it.

I’ve glanced at some points that are noticeably absurd and barely deserve a mention but I’ll list them here…

What makes volume so special instead of frequency?
you first tried blaming SI units


Those points along with a few others were worth the chuckle of having a thread named in my honor. lol.

Gene

[Folly]

It seems what we measure to infer the temperature of the sun is actually power along a spectral interval. That point seems well established. We are indeed not actually measuring the average kinetic energy of the sun (temperature); we infer it.

Well, yes. All temperature measurements are indirect. It is, however, incorrect to say you can measure the temperature of your cup of coffee if you also say that you can not measure the temperature of the sun.

I’ve glanced at some points that are noticeably absurd and barely deserve a mention but I’ll list them here…

What makes volume so special instead of frequency?

you first tried blaming SI units


Those points along with a few others were worth the chuckle of having a thread named in my honor. lol.


They are ridiculous indeed, AgingYoung, and it's sad that you have implicitly made these points. It's worse that after everything mentioned, you still don't even have the first point right: it's thermal expansion compared to blackbody radiation, volume compared to intensity.

Using a mercury thermometer involves making a measurement of length, based on a change of volume based on thermal expansion. You say this is direct. One can also measure the temperature by measuring the intensity of multiple frequencies of the emitted blackbody radiation. You say this is indirect. One measures length, the other intensity. One works based on thermal expansion, the other works based on blackbody radiation.

Your original argument talks about some units being derived, with this being an important distinction in measurement. I can't find anything to support this, and you don't seem to be able to either. Even worse, intensity, length, and temperature are all base SI units. If you're happy with temperature to length, you should be equally thrilled with temperature to intensity.


Please answer the question from the previous post, which I have summarised below (so that it's available on the same page.)

Measuring the temperature of the sun by looking at the relative intensities of emitted blackbody radiation is indirect in the non process control sense. So is measuring a length that changes based on thermal expansion. Either would be direct in the process control sense because the temperature of the Sun is being measured, not some other related temperature.

If you still disagree, and insist that there is yet another well known (?!) distinction that says we can't measure the surface temperature of the sun, please find some reference explaining this, and then explain why it's more appropriate than either of the other common usages.

[Cuddles]

We are indeed not actually measuring the average kinetic energy of the sun (temperature); we infer it.

And since this is true for every single measurement of any temperature that will ever be made, why do you try to distinguish between different measurements? As has been pointed out many times, all measurements are indirect, so given that you have now admitted that it is absurd to make a distinction between deriving a temperature from volume and deriving one from frequency :
I’ve glanced at some points that are noticeably absurd and barely deserve a mention but I’ll list them here…
What makes volume so special instead of frequency?
Do you now admit that you were wrong to claim we cannot measure the temperature of the Sun? Or alternatively, admit that we cannot measure the temperature of anything?

[AgingYoung]

And since this is true for every single measurement of any temperature that will ever be made, why do you try to distinguish between different measurements?
The point I made was there is a distinction made in the curricula of instrumentation.

Do you now admit that you were wrong to claim we cannot measure the temperature of the Sun? Or alternatively, admit that we cannot measure the temperature of anything?

I love choices. This is too funny. The fact is an instrument that changes based on its thermal characteristics dynamically responds to the average kinetic energy (temperature) either directly to the process it's in or indirectly. The quantity causing the change in the instrument is temperature.

Instrumentation used to infer the surface temperature of the sun directly responds to other quantities; not temperature. Scientists (some of which are Nobel recipients) set these standards for measurements and define the terms. I would like to say that although I'm aware of how they look at things, I'm not responsible for their decisions.

Gene

[Cuddles]

Leaving aside your impressively random bolding and equally random appeal to authority, you initially said, as quoted in the OP, that measuring the temperature of something by measuring frequency is different from measuring the temperature of something by measuring length. Having had it explained to you many times, in many different ways, are you really refusing to admit that there is no meaningful distinction that can be made?

[davefoc]

One of the things this thread has made me think about is how the temperature scales were established originally.

Given that there is not a method of measuring temperature directly, all temperature measurements are based on formula that relates the relationship between temperature and some other property that can be measured.

But when somebody is trying to do this for the first time there is no formula. OK one might use PV=nRT and measure volume of a gas to establish a temperature scale, but this formula is not perfect and unless you have a way of measuring the temperature you can't determine how far from perfect it is.

[AgingYoung]

Dave,

Good points. At some point standards have to be agreed on so people can exchange ideas. It's essential that terms have meaning for communication to happen. At times people use terms that have various meanings in common language yet the same term has an exact meaning in a given discipline. Law is probably the most varied in that regard. A lot of times when law is passed there is an explanation of terms used in the law. What 'deadly force' means in one law might be different in another law. They take the time to define terms so there isn't any confusion. Lawyers try to induce confusion in spite of any effort by legislatures to nip it at the bud. That's life.

The base quantity thermodynamic temperature assumes two points of average kinetic energy:

absolute zero
and the triple point of specially prepared (VSMOW) water.


This structure of measurements and quantities developed by world renowned scientists (some of whom are Nobel laureates) over time up to the present moment seems to have served everyone pretty well. To be sure there are some of the opinion that those aforementioned geeks, nerds and dilberts shouldn't be imposing their views of measurements on everyone else. Not too democratic I suppose is the objection.

Mean Gene

[AgingYoung]

I feel comfortable maintaining that ALL measurements of any kind whatsoever are indirect. My rationale is that we cannot experience reality itself directly, but do so only through the signals delivered to our brains by our nervous system. Thus, no matter what we think we are measuring, what we are actually measuring is the frequency of nerve impulses from some input or other. And that's only if you admit that "you" and "I" actually EXIST.

This does strike at the very idea of what a person is. Depending on how you look at it you might say the real 'you' incorporates a telemetry system (sensors, nerves, brain, etc.) to sense reality.

Even when you consider a person and reality at that level, there is a difference between using your eyes to sense differences in average kinetic energy (or temperature) vs. using the sense of your finger or wrist. Also your wrist or finger would have a most difficult time discerning different frequencies of visible light but your eyes (unless you’re color blind) would do nicely for that function.

Cooking is a good example of this difference in the sort of quantity sensed. At times you can look at the product and know it's at the right temperature without either directly or indirectly measuring the average kinetic energy of the 'brew'. By seeing the color or consistency you 'know' or infer it's at the proper temperature.

mean Gene

[Folly]

This structure of measurements and quantities developed by world renowned scientists (some of whom are Nobel laureates) over time up to the present moment seems to have served everyone pretty well. To be sure there are some of the opinion that those aforementioned geeks, nerds and dilberts shouldn't be imposing their views of measurements on everyone else. Not too democratic I suppose is the objection.

There probably are such people. There are, after all, people willing to believe all sorts of tripe, like free energy or space based particle weapons being used in the WTC attack. All I've seen so far, however, are people who say you are wrong, AgingYoung. Not the same thing.

You still havn't answered my question.

Measuring the temperature of the sun by looking at the relative intensities of emitted blackbody radiation is indirect in the non process control sense. So is measuring a length that changes based on thermal expansion. Either would be direct in the process control sense because the temperature of the Sun is being measured, not some other related temperature.

If you still disagree, and insist that there is yet another well known (?!) distinction that says we can't measure the surface temperature of the sun, please find some reference explaining this, and then explain why it's more appropriate than either of the other common usages.