Thread: Metrology

A few more pictures..

The temperature monitoring overview..

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Nice little Tesa.. apparently not rigid enough..
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B&S CMM system with Renishaw probe... note the calibration ball on the table.

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Something to aspire to...
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Regards
Ray

Originally Posted by Anorak Bob

Precision: The Measure of All Things, BBC Four | TV reviews, news & interviews | The Arts Desk

Thanks BT, I've only watched part 2 so far, but it's fascinating stuff, the part about the Australian guy who does the polishing on the silicon is just unbelievable, to think that someone can do that sort of work just by feel is mind boggling...

so far beyond what is possible with machines ... the guy from the German Metrology Institute said he must be able to "feel' the atomic structure to get that level of precision.

A bit more from Roundest objects in the world created - tech - 01 July 2008 - New Scientist

Smooth and round

The ACPO team used techniques similar to the way Isaac Newton ground lenses for his telescopes 300 years ago. Opticians manipulated two spinning rotors to grind the surface by hand. After months of sanding, the team produced two spheres with diameters of 93.75 millimetres.
The mass of each sphere matches that of the Australian copy of the kilogram. The small-scale roughness of the balls varies by only 0.3 nanometres, and their curvature by 60 to 70 nanometres.
"If you were to blow up our spheres to the size of the Earth, you would see a small ripple in the smoothness of about 12 to 15 mm, and a variation of only 3 to 5 metres in the roundness," Leistner told New Scientist.
This kind of roundness was not possible 20 years ago, according to Leistner, because we could not see variations on this scale. Also, advances in computer processing have improved the speed at which data can be decoded from measuring devices such as the talyrond, a spindle-like instrument that rotates around the ball and can detect deviations from perfect roundness down to about 5 nanometres. That allows researchers to quickly correct any imperfections they find.

The Taylor Hobson Talyrond they are referring to is the same type as the instrument that you can see in Harty's pictures that's in the big glass case. Measurements down to 5 nanometers is no mean feat... that's 0.005 microns.. !! Even our Laser interferometer maxes out at 10 nanometers.. although we could always roll out the x36 resolution extender I guess...

And this guy Achim Leistner does 0.3 nanometers by feel...



Image from New Scientist link above..

Regards
Ray

One of the aims of the Si Sphere Project was to remove the need for the Standard kg which is the last artefact based fundamental quantity.
The proposal was to use the spheres to help define Avagadro's number and hence the mole and thus define mass via the mole.
The Chemists like this as it defines the mole in terms of entities and that's what chemists think of (atoms + molecules)

The Physicists have different ideas and have proposed that mass be defined using E= m c^2.
"c" is known to a great number of significant figures and E can also be measured electrically with high precision so m can down be defined better than using an artefact.
Many chemists do not like this as their concept of entities takes a back seat over the cumulative or statistical methods of physicists.
However, the world wide body representing chemists (the International Union of Pure and Applied Chemistry or IUPAC) accepted this proposal last year.
The ramifications of this decision is still being examined by National measurement institutes worldwide but is expected to be ratified in a year or two's time.

Originally Posted by BobL

One of the aims of the Si Sphere Project was to remove the need for the Standard kg which is the last artefact based fundamental quantity.
The proposal was to use the spheres to help define Avagadro's number and hence the mole and thus define mass via the mole.
The Chemists like this as it defines the mole in terms of entities and that's what chemists think of (atoms + molecules)

The Physicists have different ideas and have proposed that mass be defined using E= m c^2.
"c" is known to a great number of significant figures and E can also be measured electrically with high precision so m can down be defined better than using an artefact.
Many chemists do not like this as their concept of entities takes a back seat over the cumulative or statistical methods of physicists.
However, the world wide body representing chemists (the International Union of Pure and Applied Chemistry or IUPAC) accepted this proposal last year.
The ramifications of this decision is still being examined by National measurement institutes worldwide but is expected to be ratified in a year or two's time.

I like this concept but can anyone explain to me how I can calibrate my scales using E=mc²? I clearly remember and understand moles from school chemistry but the theory of relativity was always just a concept which I just had to accept as the theory of a great man even t5ho I had no real understanding of the mechanics so to speak. That great man, so I was told lamented later in life that he had only had one good idea in his life! He also did not care what colour socks he wore. I like it.

Dean

Originally Posted by Oldneweng

I like this concept but can anyone explain to me how I can calibrate my scales using E=mc²? I clearly remember and understand moles from school chemistry but the theory of relativity was always just a concept which I just had to accept as the theory of a great man even t5ho I had no real understanding of the mechanics so to speak. That great man, so I was told lamented later in life that he had only had one good idea in his life! He also did not care what colour socks he wore. I like it.

Dean

No "everyday" body one uses the 1 Kg artefact that is held in Paris as "The kilogram" to calibrate their scales either.
The current standard kg(s) (there are more than one) is used to calibrate secondary standard masses and these are used to calibrate tertiary standard or calibration weights etc, so that finally sets of calibration weights are made up for sale to anyone that wants to check their scales.
All that the new definition will do is change the first step. It will not change the existing calibrations weights that are already in used

Originally Posted by BobL

No "everyday" body one uses the 1 Kg artefact that is held in Paris as "The kilogram" to calibrate their scales either.
The current standard kg(s) (there are more than one) is used to calibrate secondary standard masses and these are used to calibrate tertiary standard or calibration weights etc, so that finally sets of calibration weights are made up for sale to anyone that wants to check their scales.
All that the new definition will do is change the first step. It will not change the existing calibrations weights that are already in used

Thanks for that explanation Bob, buuutt you do keep taking the bait LOL.

Cheers

Dean

PS I was a science nerd at school and I still remember most of it now!

Originally Posted by Oldneweng

Thanks for that explanation Bob, buuutt you do keep taking the bait LOL.
Cheers
Dean
PS I was a science nerd at school and I still remember most of it now!

Happy to take the hook. Seeing as I'm on an international Scientific Panel that discusses these things it's sort of part of my brief to promote this stuff any way.
In fact in two weeks time I'll be going to Turkey for exactly this.

How do they measure a kg?

I thought a kg was solely dependent on gravity and gravity varies every so slightly at different places in the world...

Originally Posted by .RC.

How do they measure a kg?

I thought a kg was solely dependent on gravity and gravity varies every so slightly at different places in the world...

Hi .RC.

Well there's Kg mass and Kg force, a Kg mass is still a Kg even when weightless in outer space, a Kg force is the force exerted by earth's gravity on a 1 Kg mass...

How do you measure a Kg, well that's the real problem. You use a balance and compare the unknown mass with a known standard.... what is the standard...



Regards
Ray

Originally Posted by .RC.

How do they measure a kg?
I thought a kg was solely dependent on gravity and gravity varies every so slightly at different places in the world...

Mass and it's unit the kg has very little to do with gravity.
Mass it is simply an amount of material.

The Standard kg is a specific amount of mass and defined by a lump of metal in Paris.
The Standard is then cross referenced to a bunch of secondary standards that are all are sent to Paris and their weight is measured (under the same conditions under the same value of gravity) relative to The Standard.
These secondary standards can then go anywhere in the world and have other tertiary standards referenced against any one of them, once under the same conditions. The value of gravity may be different from one location to another but as long as the comparisons are made against a known standard all in the same location that has been correctly referenced all the way back up the chain it will be correct.

A good quality lab balance will also have inside it a certified calibration weight so balances can be moved anywhere and calibrated and still read correctly.

Measuring mass can be a serious business. I posted this a few years ago

As an aside I worked in a, Institute lab in Europe where all critical weighings that had to be certified were done by one guy (a weighing metrologist). To weigh critical amounts you had to book the guy a week in advance and he would turn up the evening before and park his trolley with all his gear in the lab where the measurements were to be done (temperature stabilization). He'd also set up a large transparent air tight glove box on a weighing bench made of marble and place everything inside the box and flood the box with Argon (minimizes buoyancy effect). Then he would set up 3 digital logging thermometers, and a set of weak radioactive sources inside the tent to minimize static. Access to the stuff inside was via the gloves. Outside the box he'd set up a laptop that logged the temp and air pressure and balance readings - he usually used 2 balances (and he had a spare one his trolley just in case)

Next morning he would check the argon pressure and temp stabilization before calibrating the balances - everything he did on the balances was logged on the laptop. Then he would do the weighings. Each sample was then weighed 10 times on each balance and stats determined. Then he would do this 3 times or until he got 3 sets of results that agreed with each other. iInally he would recalibrate the balances. No one was allowed to be in the room with him while he did the calibrations and weighings. For a single sample this took at least 2 hours. Then he would type up a brief report and put the report with all the data on the central server for general access.

The weighings were done this way because some of the results often had legal ramifications and the last thing needed was for these measurements to be disputed in court.

Thanks Bob. A bit of detailed background on how it happens. Fleshes out the knowledge one already has. I would have liked to do a tour of this site. Maybe one day.

Dean

Hi Guys
There will be another tour in about 3 or 4 weeks time. I have been talking with my Son who is happy to do another shortly.
I have a list of 6 that missed the last one for various reasons and I will put them in first. I reckon we can probably fit in another 6 if anyone else is interested.

On my list are
JHovel
Machtool
Havinago
Neksmerj
Steamwhisperer
and J Ashburn

Anyone else?

Roger

Originally Posted by RayG

Hi .RC.

. . . . . . ., a Kg force is the force exerted by earth's gravity on a 1 Kg mass...

The earth's gravity varies depending location so a kg force or weight varies accordingly.
There is something called a "standard kg weight" uses the "standard acceleration due to gravity" which is . . . . . .
Enough I think?

No wait, . . . . . "kg" is all lower case. All the order of magnitude prefixes are lower case except for a million and above.
One of the most commonly misspelt abbreviations for units is the humble millilitre (mL)
My favourite volume is the "yoctolitre" (yL) which is a cubic nanometre (nm)³ , although the "zetalitre" (zL) or cubic megametre is pretty awesome!

Blimey, it's starting to sound like Sheldon (from Big Bang) speak

Originally Posted by rogerbaker

Hi Guys
There will be another tour in about 3 or 4 weeks time. I have been talking with my Son who is happy to do another shortly.
I have a list of 6 that missed the last one for various reasons and I will put them in first. I reckon we can probably fit in another 6 if anyone else is interested.

On my list are
JHovel
Machtool
Havinago
Neksmerj
Steamwhisperer
and J Ashburn

Anyone else?

Roger

Love to be there. If I can get enough notice I may be able to swing a day off work and fly in for the day.

Michael