33 replies to this topic

[chuck_d]

Adjusted for elevation, my water boils at 210.6. I use 210F when I'm setting the kettle controller to prevent unwanted boiling.All-in-all, though, that fact is a good argument for the ice-water calibration method.

Heh, yeah, I suppose technically I should have said 211.95 I've idly wondered how much that can vary for one location based on normal changes in barometric pressure as high & low pressure systems roll through. I've yet to do the math to figure it out though.

[NomNomHopzinator]

That shouldn't matter. No matter where the thermometer was calibrated it should work everywhere (well, not in a microgravity environment ). The boiling point changes, yes, but that doesn't affect the ability of a thermometer to read the temperature at which it boils. Relativity only comes into play when two observers are traveling at high velocities with respect to each other.

Well it does matter because the temperature that you read is relative to the calibration. It isn't a matter of where the thermometer is and if it works persay, it is a matter of what you told it 100C was. In some cases, thermometers can be calibrated with boiling distilled water. If the atmospheric pressure isn't accounted for correctly then when set to 100C, the readings from then on can be slightly off from the actual temps. You are reading temperatures relative to your calibration settings....if calibrated at all. Also, another crappy factor to consider is the degree of accuracy. If your thermometer has an error of +/- 2 degrees then one can't be too bent out of shape if boiling at 210F. BTW, relativity in the theory refers to is time being relative rather than a constant. The term isn't specific to Einstein's theory although it is usually tied to it. BP is relative to atmospheric pressure. Sound frequencies are relative to velocity.... we live in a world of relativity

[chuck_d]

Well it does matter because the temperature that you read is relative to the calibration. It isn't a matter of where the thermometer is and if it works persay, it is a matter of what you told it 100C was. In some cases, thermometers can be calibrated with boiling distilled water. If the atmospheric pressure isn't accounted for correctly then when set to 100C, the readings from then on can be slightly off from the actual temps. You are reading temperatures relative to your calibration settings....if calibrated at all. Also, another crappy factor to consider is the degree of accuracy. If your thermometer has an error of +/- 2 degrees then one can't be too bent out of shape if boiling at 210F. BTW, relativity in the theory refers to is time being relative rather than a constant. The term isn't specific to Einstein's theory although it is usually tied to it. BP is relative to atmospheric pressure. Sound frequencies are relative to velocity.... we live in a world of relativity

No, it really does not matter. Ambient pressure has no impact on the operation of the thermometer. It does not matter where you calibrate the thermometer, 100 is 100 in Gaithersburg, MD just like it is in Denver, CO. Ambient pressure will impact at what temperature water boils, but not what the temperature is, which is why the ice point is most often used for calibration (high repeatability). A thermometer calibrated at NIST should work just fine in Denver.BTW, Relativity (in physics) refers to more than just time. In addition to the relativity of simultaneity, time dilation and length contraction are just a couple of the consequences of special relativity. The name relativity is not a reference to time not being a constant but to the fact that different frames of reference are being used.

Edited by chuck_d, 26 May 2009 - 04:08 PM.

[NomNomHopzinator]

No, it really does not matter. Ambient pressure has no impact on the operation of the thermometer. It does not matter where you calibrate the thermometer, 100 is 100 in Gaithersburg, MD just like it is in Denver, CO. Ambient pressure will impact at what temperature water boils, but not what the temperature is, which is why the ice point is most often used for calibration (high repeatability). A thermometer calibrated at NIST should work just fine in Denver.BTW, Relativity (in physics) refers to more than just time. In addition to the relativity of simultaneity, time dilation and length contraction are just a couple of the consequences of special relativity. The name relativity is not a reference to time not being a constant but to the fact that different frames of reference are being used.

I am not talking about NIST certified thermometers...they are fine pieces of equipment. This one is accurate within +/- 1C from -20 to 100C which is quite nice.https://www.infrared...t100-4039.shtmlWhat I am getting at is that if I calibrate my thermometer at 100C or 212F from boiling water, it will be off the mark from then on out at any temperature that I measure...even ice. To worsen the situation, if I sell it on ebay to someone in CO and they don't re-calibrate it...then it is gets even worse at measuring temps if it is based off my water boiling temp. Your CO vs MD argument is quite obvious but I am not talking about random temperature monitoring, just boiling point variation and in a certain case of calibrating to a boiling point...which probably happens a lot since it is easy to do. Thanks for the wiki explanation but lets get back to my comment that didn't need correcting. My use of the word relativity is in reference to something being dependent on on other factors. That is sound wouldn't you say?

[chuck_d]

What I am getting at is that if I calibrate my thermometer at 100C or 212F from boiling water, it will be off the mark from then on out at any temperature that I measure...even ice.

Which is why thermometers are not calibrated that way. If you happen to calibrate your own thermometer incorrectly, then of course it won't work. Use the ice point, not the boiling point and calibrate your thermometer correctly.

Your CO vs MD argument is quite obvious but I am not talking about random temperature monitoring, just boiling point variation and in a certain case of calibrating to a boiling point...which probably happens a lot since it is easy to do. Thanks for the wiki explanation but lets get back to my comment that didn't need correcting. My use of the word relativity is in reference to something being dependent on on other factors. That is sound wouldn't you say?

Nobody selling a calibrated thermometer would have used boiling water at an unknown temperature to do it. Click the NIST link I posted above and you'll see how its done. So, back to your comment that a calibrated thermometer sold would not work if it used at a different altitude than where it was calibrated... that's wrong. The temperature at which water boils changes, but not the thermometer's ability to measure that temperature.PS - Nah, actually it's not wikipedia, I just spouted random stuff I remembered from my Special Relativity class a decade ago. I could post a scan of my final if you wanted it Your use of the word is fine, just incorrect; thermometers aren't relative to ambient pressure.

Edited by chuck_d, 27 May 2009 - 12:46 AM.

[Stout_fan]

... 100 is 100 in Gaithersburg, MD ...

Chuck,There are places where logic, common sense and reality are strained a bit.Trust me, Gaithersburg is at the top of the list.DC runs a close second.

[3rd party JKor]

A thermometer is a closed system. The atmospheric pressure where it's used has no bearing on what temperature it reads.

[RommelMagic]

I can relate to that!

[toonces]

A thermometer is a closed system. The atmospheric pressure where it's used has no bearing on what temperature it reads.

um. sort of. yes, the thermometer is a closed system. the water it is trying to read the temp of isn't usually.atmospheric pressure has an enormous effect on what temperture boils waters at. like george said. where i live, at ~7200 foot altitude, i've seen water boil at 183*F. if you put water in a pressure cooler (increase the atmospheric pressure) water will boil at a much higher temp. pull a vacuum on it, it boils at a much lower temp (distillers do this).

[stellarbrew]

I think this all gets us back to chuck_d's point that an ice point is preferred for thermometer calibration in lieu of a boiling point.

[3rd party JKor]

um. sort of. yes, the thermometer is a closed system. the water it is trying to read the temp of isn't usually.atmospheric pressure has an enormous effect on what temperture boils waters at. like george said. where i live, at ~7200 foot altitude, i've seen water boil at 183*F. if you put water in a pressure cooler (increase the atmospheric pressure) water will boil at a much higher temp. pull a vacuum on it, it boils at a much lower temp (distillers do this).

atmospheric pressure doesn't affect what the thermometer reads, only what temperature water boils.

[stellarbrew]

atmospheric pressure doesn't affect what the thermometer reads, only what temperature water boils.

I may be wrong, but I think that was understood.I just get the feeling that people are missing one another's points.

Edited by stellarbrew, 27 May 2009 - 06:25 PM.

[3rd party JKor]

I may be wrong, but I think that was understood.

understood what? wait...where am I?

[stellarbrew]

understood what? wait...where am I?

That the reading of a temperature on a thermometer does not depend on the atmospheric pressure.... anyone who hasn't understood that point by now is beyond your help.