Feels like a chicken and egg senario. Let’s say I get my torque wrench from work sent off to be calibrated, and that’s calibrated with something itself needs to be calibrated, and so on and so fourth. How’s that figured out?
In: 430
Also see how to handscrape plane surfaces. There are tricks where you can craft something completely flat, starting from imperfect parts. Tricks like those are used to ‘pull up by your own hair’, which is what toolmakers have to do.
That specific trick involves scraping 3 surfaces against each other, in a way that eventually makes all 3 perfectly flat.
Testing torque is pretty easy. You apply a weight that pulls the arm of the wrench at a specific distance from the centre of the axis. And then you read the scale manually to see what it says.
“What’s on the scale if I apply 1 kilogram?”
“What’s on the scale if I apply 2 kilograms?”
“What’s on the scale if I apply 3 kilograms?”
“What’s on the scale if I apply 4 kilograms?”
“What’s on the scale if I apply 5 kilograms?”
After a while, you get a table of numbers that you can use to establish a) how much the value on the scale deviates from the actual load b) if the tool is better or worse at certain parts of the range and c) if there has been an obvious change from the precious periodic calibration.
It’s possible that the tool is fit-for-purpose for the actual user case despite that it’s overall pretty crappy, but that’s besides the scope of this explanation.
For that testing location to be fit for purpose for the testing, you need to have a) a pretty sturdy rack for the test itself because you need to be reasonably certain that the test itself is adding as few as possible of the extra unwanted force directions that will make the test useless b) a verified, digital, level c) a verified set of weights d) knowledge about your local gravity (because that shit changes a hint on the decimals even within the same city) and e) a controlled climate (you want to be able to reproduce the same – within reason – circumstances again and again and again)
The weights are pretty essential in the whole thing, so you send them to an external institute annually or biannually or so. They, in essence, put them up one by one on a scale to find out if their weight is within an acceptable margin; for some users, it may be more than enough that their 1000g weight is ⨦1g. For others, the requirement may be ⨦0.01g
Their scale is *also* in a controlled climate. Only used for the purpose of verifying the weight of…weights. It’s reliability is verified with a *reference weight* every now and then (say, monthly?) and sometimes THAT is sent to another test institute for cooperative verification of both institutes. Occasionally, they lend in a national reference weight or perhaps an international reference weight so that they can compare to what other countries, on an international *treaty* level has agreed to be a certain weight.
So that’s how it works. You test everything with reference loads. And occasionally, you let someone else verify the reference loads, effectively borrowing the credibility of THEIR reference for your own calibrations. They, in turn, borrow the credibility of someone else’s reference load.
Remember how I said that a weight is rated? E.g 1000g ⨦0.1g?
What that says, basically, is that since the weight is not guaranteed to be better than one ten thousandth of it’s full weight, then you can never offer a better rating on a calibration with that weight than 0.01% of the tools full scale reading.
In reality, you also need to factor in the reliability of the digital scale, the reliability of the instrument that was used to establish the local gravity and so on and on and on. But that is kind of out of scope for the explanation.
But, the point I was trying to make is that all of the references have an established reliability, that they have inherited from the initial reference when the reference steps are taken into account.
If you can trace a weight to how it’s weight is established and within what fault tolerance it’s weight is established, you pretty much just have to make up your mind on if your reference has good enough tolerance for it’s purpose.
Oh shit! There’s never questions like this that I’m qualified to answer, however this one I can!
As stated by another redditor, there is what’s considered NIST traceability.
What that means is that there is an unbreakable chain of traceability back to the “standard” of measurement that all other measurements that can be derived from start at. This is agreed upon at an international level.
An oversimplification of this is that you imagine somewhere there’s a vault with a perfect block that measures 100 cm in length. (Example, not how it’s actually done)
It’s protected and is what everything that length is measured in is derived from. Inches, meters, feet, kilometers, acres, etc.
Every few years, very high accuracy secondary measuring “standards” are compared against the master standard.
This establishes the first level of traceability.
Each level of measurement down the line from that increases the “uncertainty” of measurement to account for variations in accuracy, human error, etc.
If you have ever seen a zombie or vampire movie, imagine that patient zero is the “master standard” and every zombie or vampire derived from that is a “little less perfect” than that singular top level unit.
For usage as calibration standards, there’s a guideline called the rule of 4 that stipulates when calibrating something, the standard you compare it against is at least 4 times as accurate as the unit under test.
i.e. if you are measuring a ruler that is accurate to 0.1 cm, the standard you compare against should be at least 0.025 cm accurate.
This helps retain that accuracy down the line for long periods of time.
Any device used for measuring is calibrated to some extent. Calibration is basically just comparing scales.
The tool used for comparison / calibration itself is manufactured at a higher accuracy level and therefore more exact. Say if you want to measure distance in a 1km accuracy, the tool you use for calibration should be accurate to at least 0.1km. This is why the super accurate devices are used in very controlled environments.
There is an ultimate definition for each unit, in the past that might be a physical object, but more recently we’ve been switching to physical constants. To calibrate your torque wrench you ultimately need reference standards for mass, distance, and time.
For time we defined the resonant frequency of a cesium atom, so a specific count of oscillations equals one second.
For distance we fixed the value of the speed of light. So the distance light travels in one second. This works because we already established the second, and interferometry can be used to get very precise distance measurements.
And for mass we fixed the value of the Planck constant, which relates energy to frequency, and because of mass-energy equivalence also relates mass to frequency. In more practical terms, we create a sphere of ultra pure silicon, which has a known crystal structure and which has been refined isotopically, so we know the atomic mass and can count the number of atoms extremely precisely.
So once we have these standards:
force = mass * acceleration
newtons = kilograms * meters / (seconds * seconds)
torque is force applied tangentially at a distance, so newtons * meters.
If you want that in inch pounds, those are defined in terms of SI units.
Calibration of microphones/speakers is one I’d like to hear about. How do you break out of that self referential loop?
For complex machines, you calibrate using an Asset that is known to be in good working order.
If you know what output your supposed to get from that asset, then you know what your machine should be outputting.
But all in all, there is a reason precision tools, and their technicians, are expensive as Fuck.
A calibration standard is, in general, calibrated to a better quality standard at a higher laboratory with better comparison equipment. However, at some point, there has to be a top laboratory with a reference standard which is the end of the chain.
Historically, this was with special specimens kept in very careful conditions, which were carefully built. For example, for many years, a laboratory in Paris kept a stick with two marks 1 meter apart engraved on it, and this was the reference meter. Another laboratory might get a stick and put two marks on it – but it would then have to be shipped to Paris, and measured against the reference meter stick. The lab would then key a record of the exact length.
These days, measures have been redefined to something fundamental which you can measure with a scientific experiment. The official meter is no longer the length of a stick in Paris, but there is an equation for the length of a meter as compared to the result of a scientific experiment. For example, top calibration labs don’t have use sticks as their top reference any more. Instead, they have a scientific apparatus which can perform a laser spectroscopy experiment which allows the time it takes for light to travel a certain distance to be measured. The lab can put a stick in the apparatus, and it will be able to give the exact length based on the equation and the result of the experiment.
Similarly, the second used to be defined as a fraction of the length of the day. A calibration laboratory would do an experiment to measure the height of the sun, and they could compare a clock to when the sun reached it’s highest point in the day marking noon. These days, the second is now defined as a multiple of the frequency of a specific transition of a cesium atom. This transition frequency can be measured by microwave spectroscopy, and you can compare a clock to the transition, and you can adjust the clock as needed. In fact, you can go out and buy an atomic clock, which is just a good quality clock, packaged with a spectroscopy apparatus and an auto-adjust system which checks the clock against the spectroscopy apparatus hundreds of times per second and adjusts the clock as needed.
Super captivating BBC Documentary about measurments and weight standards. They know how to tell a story. https://www.youtube.com/watch?v=XofuloR6x74
The SI system is what defines meters, seconds, kilograms, Newtons etc. Your wrench may use foot-pounds-force, but feet and pounds-force are nowadays defined as certain numbers of meters and Newtons.
The SI system is defined in such a way that scientists can carry out experiments to get the length of a meter etc precisely.
For example, a particular atom in a particular state will give off radio waves with a specified number of waves per second. By counting waves, you can measure a second. And this is not an approximation, the second is defined as the time it takes for a certain number of waves.
Another example: Light and radio waves travel through vacuum at a fixed speed, which is specified in the SI standard. Using an accurate clock (see previous paragraph), you can measure how far light goes in a certain fraction of a second, and that is a meter.
Of course, all the above is completely impractical for day to day use.
So there are a small number of labs worldwide, typically one per country, which specialise in measurement. They will have a number of standards, such as 1kg lumps of metal or metal sticks with two marks precisely 1m apart. Those standards will have been checked by the experiments above, or against standards that were calibrated against those experiments. (E.g. There are only a handful of labs that have done the kilogram experiment).
In turn, those standards will be used to calibrate other standards or measuring devices, which will be used to calibrate other standards or measuring devices, and this repeats many times until one of those calibrated devices is used to calibrate your wrench.
Each time you calibrate something you end up with less accuracy than you started with. But your wrench probably doesn’t need to be accurate to one part per million, even one part per thousand is probably overkill.
Feels like a chicken and egg senario. Let’s say I get my torque wrench from work sent off to be calibrated, and that’s calibrated with something itself needs to be calibrated, and so on and so fourth. How’s that figured out?
In: 430
Also see how to handscrape plane surfaces. There are tricks where you can craft something completely flat, starting from imperfect parts. Tricks like those are used to ‘pull up by your own hair’, which is what toolmakers have to do.
That specific trick involves scraping 3 surfaces against each other, in a way that eventually makes all 3 perfectly flat.
Testing torque is pretty easy. You apply a weight that pulls the arm of the wrench at a specific distance from the centre of the axis. And then you read the scale manually to see what it says.
“What’s on the scale if I apply 1 kilogram?”
“What’s on the scale if I apply 2 kilograms?”
“What’s on the scale if I apply 3 kilograms?”
“What’s on the scale if I apply 4 kilograms?”
“What’s on the scale if I apply 5 kilograms?”
After a while, you get a table of numbers that you can use to establish a) how much the value on the scale deviates from the actual load b) if the tool is better or worse at certain parts of the range and c) if there has been an obvious change from the precious periodic calibration.
It’s possible that the tool is fit-for-purpose for the actual user case despite that it’s overall pretty crappy, but that’s besides the scope of this explanation.
For that testing location to be fit for purpose for the testing, you need to have a) a pretty sturdy rack for the test itself because you need to be reasonably certain that the test itself is adding as few as possible of the extra unwanted force directions that will make the test useless b) a verified, digital, level c) a verified set of weights d) knowledge about your local gravity (because that shit changes a hint on the decimals even within the same city) and e) a controlled climate (you want to be able to reproduce the same – within reason – circumstances again and again and again)
The weights are pretty essential in the whole thing, so you send them to an external institute annually or biannually or so. They, in essence, put them up one by one on a scale to find out if their weight is within an acceptable margin; for some users, it may be more than enough that their 1000g weight is ⨦1g. For others, the requirement may be ⨦0.01g
Their scale is *also* in a controlled climate. Only used for the purpose of verifying the weight of…weights. It’s reliability is verified with a *reference weight* every now and then (say, monthly?) and sometimes THAT is sent to another test institute for cooperative verification of both institutes. Occasionally, they lend in a national reference weight or perhaps an international reference weight so that they can compare to what other countries, on an international *treaty* level has agreed to be a certain weight.
So that’s how it works. You test everything with reference loads. And occasionally, you let someone else verify the reference loads, effectively borrowing the credibility of THEIR reference for your own calibrations. They, in turn, borrow the credibility of someone else’s reference load.
Remember how I said that a weight is rated? E.g 1000g ⨦0.1g?
What that says, basically, is that since the weight is not guaranteed to be better than one ten thousandth of it’s full weight, then you can never offer a better rating on a calibration with that weight than 0.01% of the tools full scale reading.
In reality, you also need to factor in the reliability of the digital scale, the reliability of the instrument that was used to establish the local gravity and so on and on and on. But that is kind of out of scope for the explanation.
But, the point I was trying to make is that all of the references have an established reliability, that they have inherited from the initial reference when the reference steps are taken into account.
If you can trace a weight to how it’s weight is established and within what fault tolerance it’s weight is established, you pretty much just have to make up your mind on if your reference has good enough tolerance for it’s purpose.
Oh shit! There’s never questions like this that I’m qualified to answer, however this one I can!
As stated by another redditor, there is what’s considered NIST traceability.
What that means is that there is an unbreakable chain of traceability back to the “standard” of measurement that all other measurements that can be derived from start at. This is agreed upon at an international level.
An oversimplification of this is that you imagine somewhere there’s a vault with a perfect block that measures 100 cm in length. (Example, not how it’s actually done)
It’s protected and is what everything that length is measured in is derived from. Inches, meters, feet, kilometers, acres, etc.
Every few years, very high accuracy secondary measuring “standards” are compared against the master standard.
This establishes the first level of traceability.
Each level of measurement down the line from that increases the “uncertainty” of measurement to account for variations in accuracy, human error, etc.
If you have ever seen a zombie or vampire movie, imagine that patient zero is the “master standard” and every zombie or vampire derived from that is a “little less perfect” than that singular top level unit.
For usage as calibration standards, there’s a guideline called the rule of 4 that stipulates when calibrating something, the standard you compare it against is at least 4 times as accurate as the unit under test.
i.e. if you are measuring a ruler that is accurate to 0.1 cm, the standard you compare against should be at least 0.025 cm accurate.
This helps retain that accuracy down the line for long periods of time.
Any device used for measuring is calibrated to some extent. Calibration is basically just comparing scales.
The tool used for comparison / calibration itself is manufactured at a higher accuracy level and therefore more exact. Say if you want to measure distance in a 1km accuracy, the tool you use for calibration should be accurate to at least 0.1km. This is why the super accurate devices are used in very controlled environments.
There is an ultimate definition for each unit, in the past that might be a physical object, but more recently we’ve been switching to physical constants. To calibrate your torque wrench you ultimately need reference standards for mass, distance, and time.
For time we defined the resonant frequency of a cesium atom, so a specific count of oscillations equals one second.
For distance we fixed the value of the speed of light. So the distance light travels in one second. This works because we already established the second, and interferometry can be used to get very precise distance measurements.
And for mass we fixed the value of the Planck constant, which relates energy to frequency, and because of mass-energy equivalence also relates mass to frequency. In more practical terms, we create a sphere of ultra pure silicon, which has a known crystal structure and which has been refined isotopically, so we know the atomic mass and can count the number of atoms extremely precisely.
So once we have these standards:
force = mass * acceleration
newtons = kilograms * meters / (seconds * seconds)
torque is force applied tangentially at a distance, so newtons * meters.
If you want that in inch pounds, those are defined in terms of SI units.
Calibration of microphones/speakers is one I’d like to hear about. How do you break out of that self referential loop?
For complex machines, you calibrate using an Asset that is known to be in good working order.
If you know what output your supposed to get from that asset, then you know what your machine should be outputting.
But all in all, there is a reason precision tools, and their technicians, are expensive as Fuck.
A calibration standard is, in general, calibrated to a better quality standard at a higher laboratory with better comparison equipment. However, at some point, there has to be a top laboratory with a reference standard which is the end of the chain.
Historically, this was with special specimens kept in very careful conditions, which were carefully built. For example, for many years, a laboratory in Paris kept a stick with two marks 1 meter apart engraved on it, and this was the reference meter. Another laboratory might get a stick and put two marks on it – but it would then have to be shipped to Paris, and measured against the reference meter stick. The lab would then key a record of the exact length.
These days, measures have been redefined to something fundamental which you can measure with a scientific experiment. The official meter is no longer the length of a stick in Paris, but there is an equation for the length of a meter as compared to the result of a scientific experiment. For example, top calibration labs don’t have use sticks as their top reference any more. Instead, they have a scientific apparatus which can perform a laser spectroscopy experiment which allows the time it takes for light to travel a certain distance to be measured. The lab can put a stick in the apparatus, and it will be able to give the exact length based on the equation and the result of the experiment.
Similarly, the second used to be defined as a fraction of the length of the day. A calibration laboratory would do an experiment to measure the height of the sun, and they could compare a clock to when the sun reached it’s highest point in the day marking noon. These days, the second is now defined as a multiple of the frequency of a specific transition of a cesium atom. This transition frequency can be measured by microwave spectroscopy, and you can compare a clock to the transition, and you can adjust the clock as needed. In fact, you can go out and buy an atomic clock, which is just a good quality clock, packaged with a spectroscopy apparatus and an auto-adjust system which checks the clock against the spectroscopy apparatus hundreds of times per second and adjusts the clock as needed.
Super captivating BBC Documentary about measurments and weight standards. They know how to tell a story. https://www.youtube.com/watch?v=XofuloR6x74
The SI system is what defines meters, seconds, kilograms, Newtons etc. Your wrench may use foot-pounds-force, but feet and pounds-force are nowadays defined as certain numbers of meters and Newtons.
The SI system is defined in such a way that scientists can carry out experiments to get the length of a meter etc precisely.
For example, a particular atom in a particular state will give off radio waves with a specified number of waves per second. By counting waves, you can measure a second. And this is not an approximation, the second is defined as the time it takes for a certain number of waves.
Another example: Light and radio waves travel through vacuum at a fixed speed, which is specified in the SI standard. Using an accurate clock (see previous paragraph), you can measure how far light goes in a certain fraction of a second, and that is a meter.
Of course, all the above is completely impractical for day to day use.
So there are a small number of labs worldwide, typically one per country, which specialise in measurement. They will have a number of standards, such as 1kg lumps of metal or metal sticks with two marks precisely 1m apart. Those standards will have been checked by the experiments above, or against standards that were calibrated against those experiments. (E.g. There are only a handful of labs that have done the kilogram experiment).
In turn, those standards will be used to calibrate other standards or measuring devices, which will be used to calibrate other standards or measuring devices, and this repeats many times until one of those calibrated devices is used to calibrate your wrench.
Each time you calibrate something you end up with less accuracy than you started with. But your wrench probably doesn’t need to be accurate to one part per million, even one part per thousand is probably overkill.
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