Sciencemadness Discussion Board - Help wanted ... calibrating a 2kg F1 calibration weight.

Help wanted ... calibrating a 2kg F1 calibration weight.

Sulaiman - 13-5-2019 at 20:08

I am bidding on a calibration weight, already at my maximum/only bid
https://www.ebay.co.uk/itm/Mettler-Calibration-test-weight-F...
(feel free to outbid me if useful to you)
It is >25 years old = out of calibration, even discounting scratches etc.
so it is no longer F1 class,
but it is of excellent material.
so
IF my bid wins,
is there anyone within quick/cheap postal range of England who would be willing and able to measure the weight for me and post it to me ?
I'd pay postage etc.
I do not need a certificate, just an accurate measurement.
IF I win this would become my primary reference for my hoped for lab after relocating.

If you think that you may be able to help then please feel free to U2U me to avoid mass random requests

My bid just won the 2kg mass/weight.

Sulaiman - 15-5-2019 at 04:00

Anyone able to weight it accurately for me ?

(M1 class accuracy of +/- 100 mg absolute error would be good enough,
less error (e.g. F1 class = +/- 10 mg) would of course be preferable)

fusso - 15-5-2019 at 10:23

Isn't sending it to a calibration company faster than looking for someone here who's able to do it?
I doubt there will be anyone who has such accurate equipment.

unionised - 15-5-2019 at 11:05

Quote: Originally posted by fusso

Isn't sending it to a calibration company faster than looking for someone here who's able to do it?
I doubt there will be anyone who has such accurate equipment.

Maybe.
But if it was a 200g weight, I'd offer to weigh it in the lab at work.
Not strictly "traceable" but probably good to a few 10s of mg.

And a hell of a lot cheaper than getting it done "officially".

Sulaiman
You might want to try contacting the local Trading Standards office.

phlogiston - 15-5-2019 at 12:24

I'd be happy to measure it to 10 mg accuracy on a scale that is traceable to a primary standards, and have send an U2U.

However, I am in the Netherlands. Maybe someone closer to Sulai can do it and keep shipping costs down?

Heptylene - 15-5-2019 at 15:06

Damn 20£! A chunk of stainless that size is probably worth more, let alone a calibration weight, even out of calibration!

As for weighing it, I can't help you, but maybe wait until you get it to see if it looks damaged?
Is there a reason to think the mass has changed in 25 years? (apart from mistreatment by the previous user). I ask because I bought an F1 weight (200 g) for my scale, and I hope it will lask a long time given how expensive it was.

fusso - 15-5-2019 at 15:21

Quote: Originally posted by Heptylene

Damn 20£! A chunk of stainless that size is probably worth more, let alone a calibration weight, even out of calibration!

What SS grades worth £10 per kg?

Sulaiman - 15-5-2019 at 16:52

Quote: Originally posted by fusso

Quote: Originally posted by Heptylene

Damn 20£! A chunk of stainless that size is probably worth more, let alone a calibration weight, even out of calibration!

What SS grades worth £10 per kg?

The steel has been processed to be suitable for the task - vacuum-refined, electro-polished etc.

I expect my sample to show signs of wear, I'll soon find out how much.
(>25 years ago the original mass would have been manufactured to about 2,000.004 +/-0.005 g,
which allowed for a little wear, yet remain within the calibration class limit of 2.000.00 +/-0.01g )
So my weight will be low on mass - by how much ?
I don't really care what the actual mass is, I just want a known mass to some level of confidence that I can use as my reference in future.
I consider this a little extravagent for my hobby but future alternatives will probably be more expensive,
and I'm that odd kind who likes irrelevant details, fundamental units etc.
(for reference, the cheapest new 2kg +/- 10mg mass I could find with a quick search - after I'd bid impulsively... over £200 with certificate)
That's rather a lot for my hobby !

Now that phlogiston has mentioned it - he offered help that I hope to make use of -
subject to each of our circumstances, and post.

P.S. some of the information that I found useful regarding my weight
https://www.mt.com/gb/en/home/products/Laboratory_Weighing_S...

Attachment: OIML Weight.pdf (1.1MB)
This file has been downloaded 326 times

and this manual copied from Mettler Toledo (I hope they want free marketing)
Section 7 gives good general instructions on how to weigh stuff, density etc.

Attachment: ME_Models_OI_en_30045655A.pdf (4.5MB)
This file has been downloaded 820 times
----------------------------------------------------------------------------------------
@heptylene: "Is there a reason to think the mass has changed in 25 years?"

Yes ... Handling !
e.g. the US working 1kg standard (K4) lost about 1ug/year recently, due to very very careful but frequent handling.
All of the precision masses that I've looked at recently give a 25 year (or less) lifetime.
But by then you will probably be able to count the atoms ... or feel the force ...

By comparison, my eBay Chinese M-class chrome-plated weights are showing significant signs of corrosion after four years in my lab.
(but the weight change (even for my 100g weights) is not measurable on my 10mg resolution scales)

[Edited on 16-5-2019 by Sulaiman]

Calibration weight

sodium_stearate - 16-5-2019 at 10:47

This reminds me of the time I wanted to calibrate
my newly concocted home-made beam balance.

I was using some #8 lockwashers as the weights.
Tested those to find they are all within a reasonable
tolerance of being the same weight for my purposes.

So, I've been working ever since in my world of "washers"
for the weights of materials in this simple process I've set
up. Works great. Results very accurately repeatable.

But then I also wanted to know what the actual average weight
of these washers is. So, I borrowed the 1.000 oz. calibration
weight from the post office a few blocks away. Had it just a
long enough time to weigh it and determined that 106 of those
washers balances the 1.000 oz cal. weight.

So, while I had it, I grabbed some other bolts, washers,
and a a bit of wire, and I made up a weight which
accurately balances with the post office cal. weight.

I essentially made a copy of the USPS weight which I've been
using ever since.

Then I took the USPS's weight back to the post office.

Good luck with your big cal. weight.
It should be plenty accurate enough.

CharlieA - 16-5-2019 at 11:40

How about calibrating all of your M-class weights to one of them designated as "MSM" (My standard mass). At a later date, as necessary, the MSM can be measured against a known standard weight. I assume that any one of the weights that you choose for MSM is really not that far off in accuracy, for most if not all practical purposes. I think that my personal concern concerns achieving precision more than accuracy.

unionised - 16-5-2019 at 13:18

Just a thought.
Imagine some kind soul offers to weigh your weight for you.
That means posting it to them, and them posting it back.
Imagine, instead, that you weigh a rock that's near 2Kg against your nice shiny weight and find that it's apparently 1.9123 kg.
Then you post the rock to your friend and they weigh it (accurately) and find that it's actually 1.94567Kg
they tell you the accurate mass of the rock and you can calculate the accurate mass of your 2kg mass.
They then chuck the rock in the garden and save the price of return postage.

Don't forget to account for buoyancy of the air.

It also means that, if anything gets damaged in the post, it's just a rock.

Ubya - 16-5-2019 at 14:07

Quote: Originally posted by unionised

Just a thought.
Imagine some kind soul offers to weigh your weight for you.
That means posting it to them, and them posting it back.
Imagine, instead, that you weigh a rock that's near 2Kg against your nice shiny weight and find that it's apparently 1.9123 kg.
Then you post the rock to your friend and they weigh it (accurately) and find that it's actually 1.94567Kg
they tell you the accurate mass of the rock and you can calculate the accurate mass of your 2kg mass.
They then chuck the rock in the garden and save the price of return postage.

Don't forget to account for buoyancy of the air.

It also means that, if anything gets damaged in the post, it's just a rock.

the rock should be dustless, absolutely clean, hard (to not lose bits during shipping). it would be easier a chunk of metal painted and bubble wrapped

[Edited on 16-5-2019 by Ubya]

Sulaiman - 16-5-2019 at 18:00

There are options but,
I have no scales that can measure 2 kg with 10 mg resolution,
and, I'm pushed for time,
and the mass is fairly robust - reasonable packaging should suffice.
2kg/(7.95 +/-0.14 g/cm³) = a solid lump of steel, the size of a 250 ml beaker
-----------------------------------------------------------------------------------
Update : A beautiful piece of stainless steel arrived today, it has very minor scratches etc.
I've not found a fast but cheap courrier so I've U2U'd phlogiston
... I shall not be sending this mass for weighing/checking/calibration.

Unfortunate but I hope that as the mass is cosmetically good,
the weight will be close enough to 2,000 g for most of my purposes.

Relying on 'it looks ok so it should be ok after 25 years of use'
rather than an accurate weighing, is not ideal,
but it will have to suffice for now

[Edited on 17-5-2019 by Sulaiman]

phlogiston - 17-5-2019 at 00:50

For very accurate weights, washers, nuts and bolts are not very suitable because they can easily become magnetised, even if their mass is probably pretty stable if handled carefully.
Calibration services also check magnetic susceptibility and magnetisation of reference weights for that reason.

Probaly doesn't matter for most of us, but still interesting to know.

[Edited on 17-5-2019 by phlogiston]

Heptylene - 17-5-2019 at 07:41

Quote: Originally posted by unionised

You'd want to have a rock that doesn't absorb moisture either.

Sulaiman - 17-5-2019 at 19:57

A rock would be a poor choice due to absorbtion, adsorbtion, porosity, roughness, surface contamination, ......
and unknown volume or density (bouyancy)

e.g. for my F1 class 2kg mass, the mass error should be +/- 10mg
but the same volume of air as the mass weighs c300mg (compensations are required).

on the positive side, I calculated that if the mass was once exactly 2kg,
then to go out of tolerance would require 1.25 cubic millimeter of material to be removed

over 25 years of use