PF Sense: slag router
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There's actually a reasonable explanation for this: PF Sense unwisely allows you to change its IP address in the config without applying that change and without disabling http referer tests. (And also without changing DHCP settings, which could lead to further issues if your new subnet wasn't a superset of your old one, as was the case for me.) The test prevents you from applying the new IP settings (you wind up just having to reboot the router/firewall/whatever it is you're using PF Sense for), and causes all sorts of error messages in the UI, including apparently an HTTP/501 from whichever request populates thermal sensor data.
Fortunately for my kitchen table, the router was about two orders of magnitude cooler than this.
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@vaelynphi said in PF Sense: slag router:
HTTP/501 from whichever request populates thermal sensor data.
Does that mean they're sending temperature data as an HTTP status code?
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@ben_lubar My guess would be that they send the temperature as a (text) number in the body, and whatever that is that is displaying the temperature just grabs whatever number it finds. The error message probably says "501 Not Implemented" in the body, so the consumer grabs the number and displays it.
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Since the typical display is something like "Zone 1: 50C", I suspect the typical response comes as $SensorName:$SensorValue$Unit, and the server is responding "Error: $number" so the UI is dutifully displaying it, formatting (notice the bold) and all. Unfortunately I didn't save the exact response data when this was happening, as I was mostly concentrating on getting the box running correctly. (It and all the equipment that go with it are going in on Monday, so prep time was a concern.)
Of course, in all this crazy, TRWTF is arguably that Unifi quietly and mysteriously breaks on Java 9, and outright seems unable to work with MongoDB's "Community" version. (Some will say TRWTF is using Mongo, and they're not wrong...)
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Apparently some people have experienced this same issue destructively: https://www.reddit.com/r/PFSENSE/comments/7yga4q/sg3100_inaccessible_after_a_simple_ip_change/
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@vaelynphi said in PF Sense: slag router:
Fortunately for my kitchen table, the router was about two orders of magnitude cooler than this.
501°C is 774K. Two orders of magnitude less is about 7K. Which is -265°C or -446°F. Your kitchen table is an awesome cryogenics lab!
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@dkf
approved.
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@dkf said in PF Sense: slag router:
@vaelynphi said in PF Sense: slag router:
Fortunately for my kitchen table, the router was about two orders of magnitude cooler than this.
501°C is 774K. Two orders of magnitude less is about 7K. Which is -265°C or -446°F. Your kitchen table is an awesome cryogenics lab!
Hmmh. The Celsius scale should also be absolute - both reference (melting of ice / condensation of water) points have a fixed position.
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@rhywden said in PF Sense: slag router:
Hmmh. The Celsius scale should also be absolute - both reference (melting of ice / condensation of water) points have a fixed position.
But ratios make no sense on it. You get crazy results. Absolute scales are much better precisely because ratios have proper meanings on it. (I could have used Rankine instead of Kelvin and obtained the same result, but I went with the SI unit because… well, because!)
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@dkf said in PF Sense: slag router:
@rhywden said in PF Sense: slag router:
Hmmh. The Celsius scale should also be absolute - both reference (melting of ice / condensation of water) points have a fixed position.
But ratios make no sense on it. You get crazy results. Absolute scales are much better precisely because ratios have proper meanings on it. (I could have used Rankine instead of Kelvin and obtained the same result, but I went with the SI unit because… well, because!)
I'm confused about what you consider an "absolute" scale. In my book Celsius is an absolute scale. It has two strongly defined reference points and a linear scale both for inter- and extrapolation. It's just that the zero point is on a different location than it is on the Kelvin scale.
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@rhywden There are certain physics formulae which have you multiply a temperature (rather than a difference between two temperatures) with other variables. In that case you have to use a temperature unit whose zero is absolute zero, or your results won't make sense.
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@pleegwat For example, thermal radiation involves an exponential term that simply makes no sense at all if the temperature has a negative value on the scale you use. Radiant heat transfer is proportional to T14 - T04 (not (T1 - T0)4). Changing the size of the temperature unit (e.g., Kelvin vs. Rankine) requires changing the value of a constant (Plank or Stephan-Boltzman, respectively) to match the size of the unit — not a big deal; the constants can also be used with values suitable for CGS, Imperial or cubit-shekel-hour units, if you choose (don't!). Changing the zero point of the scale requires algebraic manipulations that, basically, move the zero point to absolute zero.
You'd think a Physics teacher would have a good grasp of this.
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@hardwaregeek Yes, thank you for that last idiotic statement. You'll note that I was asking about what constitutes an "absolute scale" in his books and not what the Kelvin scale is good for.
You think a programmer would be able to grasp the difference between the two things.
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At least in english, "Absolute temperature scale" === "has a zero at absolute zero." Yes, that's not exactly what those words mean independently. It's a fixed phrase, a term of art.
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@benjamin-hall Thank you. Finally someone who answered the question and didn't interpret stupid stuff into it.
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@rhywden said in PF Sense: slag router:
@benjamin-hall Thank you. Finally someone who answered the question and didn't interpret stupid stuff into it.
An absolute scale is a system of measurement that begins at a minimum, or zero point, and progresses in only one direction. An absolute scale differs from an arbitrary, or "relative," scale, which begins at some point selected by a person and can progress in both directions. An absolute scale begins at a natural minimum, leaving only one direction in which to progress.
I rather suspect that the term absolute scale is related to absolute value in the sense that you can't have negative values. I don't think that it's reasonable to say that anyone was interpreting "stupid stuff into it."
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@boomzilla said in PF Sense: slag router:
@rhywden said in PF Sense: slag router:
@benjamin-hall Thank you. Finally someone who answered the question and didn't interpret stupid stuff into it.
An absolute scale is a system of measurement that begins at a minimum, or zero point, and progresses in only one direction. An absolute scale differs from an arbitrary, or "relative," scale, which begins at some point selected by a person and can progress in both directions. An absolute scale begins at a natural minimum, leaving only one direction in which to progress.
I rather suspect that the term absolute scale is related to absolute value in the sense that you can't have negative values. I don't think that it's reasonable to say that anyone was interpreting "stupid stuff into it."
I was talking about the last part where he implied that I don't know what the Kelvin scale is good for. This is not the TrolleyGarage and sometimes a question is just a question.
Unless we now allow insults in other topics as well. I don't find this "reasonable" in any way. You know what we call people who answered questions with: "Well, you're stupid for not getting this!"?
Assholes. That's what we call them. According to your standards, that's reasonable.
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@rhywden I dunno...your original statement about "absolute" sounded pretty nonsensical, actually. I don't think anyone seriously expects a bit of snark to be out of bounds all over the site.
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@boomzilla said in PF Sense: slag router:
@rhywden I dunno...your original statement about "absolute" sounded pretty nonsensical, actually. I don't think anyone seriously expects a bit of snark to be out of bounds all over the site.
I don't think it's "snark" to insult people. Do your job for once and tell people to put that shit in the garage.
A pretty good rule to decide whether it's "snark" or not: Would I say this to that person's face?
No? Then it's not snark.
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@rhywden said in PF Sense: slag router:
@boomzilla said in PF Sense: slag router:
@rhywden I dunno...your original statement about "absolute" sounded pretty nonsensical, actually. I don't think anyone seriously expects a bit of snark to be out of bounds all over the site.
I don't think it's "snark" to insult people. Do your job for once and tell people to put that shit in the garage.
A pretty good rule to decide whether it's "snark" or not: Would I say this to that person's face?
No? Then it's not snark.
I think you're the first person I've ever heard/seen say that Celsius is an absolute scale.
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@pleegwat said in PF Sense: slag router:
certain physics formulae
The example I think of for this is the thermodynamic efficiency of a heat-transfer mechanism, which depends on the ratio between the temperature difference between the two reservoirs and absolute temperature of the colder reservoir (assuming you're seeking to extract useful energy). The gas laws similarly require absolute temperatures to work at all, and were in fact where the concept of absolute zero was originally coined.
Many measures in physics are absolute, and others are not. Length, area, volume, pressure; all those are absolutes in normal usage. (A lot of normal usage of pressure need not actually be absolute, but we use an absolute scale anyway.) Other measures are very much not absolute: both time and position are relative measures, in part at least because we don't actually know where the origin is; we've got some approximate ideas for the time dimension, but no idea at all for space. Another relative measure is voltage; we don't actually know what the absolute potential of the Earth is, only what the potential difference between objects is.
There's nothing wrong with non-absolute scales in general (they crop up all over) but it turns out that the scales that fundamentally depend on a count of things are better off expressed as absolutes. (Except temperature in absolute scales sometimes produces irritatingly large values; I'm not used to saying that the temperature is in the low 290's…)
Absolute scale - Wikipedia
