100g +/- 0.1 mg metrology weight standard?

[Ian PParticipant @ianp]

This came from a metrology department that closed down and I have wondered what the tolerance number mean in real terms. the plus minus value of 0.1mg seems to infer that this 100 gram weight is +/- one millionth of its value.

Is that correct?

Ian P

Ian P

[Clive SteerParticipant @clivesteer55943]

Hi Ian

The item is 100 grams reference mass with a tolerance of 0.1milligrams. How much it weighs will depend on the value of gravity at the place of measurement. If you have two of these and place them on a mass balance, which look like an Apothicary’s scale, they will balance. A force balance, which is the more normal instrument for weighing, only measures the force acting on the mass due to gravity so the instrument will need a known reference mass to calibrate it and this is what these are commonly used for.

Mass standards can be toleranced to +/- micrograms and are usually made of materials that don’t oxidise and never handled.

CS

 

[Ian PParticipant @ianp]

I understand the effect of gravity and the need to use care in handling standard weights that comply to international standards.

I Googled quite a bit but could not see what class of accuracy this weight fits into.

 

Ian P

Edit, But I dont have the test certificate anyway

[Michael GilliganParticipant @michaelgilligan61133]

Rather strangely … this NPL page refers to 2019 as a time in the future … but, putting that aside, it’s a good ‘rabbit hole’

https://www.npl.co.uk/mass-mechanical-measurement/mass-standards

MichaelG.

 

.

Ref. https://www.npl.co.uk/kibble-balance

[Alan CharlestonParticipant @alancharleston78882]

Hi Ian,

Weights of this size and precision are actually quite common. Balances that were used for analytical chemistry were typically accurate to 0.1mg and I have an old Stanton balance with a capacity of 200g. Your weight would be used to make sure the balance was in calibration. Because they were balances – i.e. the weight of the sample was measured against standard weights – they were not affected by variations in gravity. This is not the case for the more modern electronic scales which measure the deflection of a beam and each balance would need to be calibrated when installed in its particular location.

Regards,

Alan C.

[Michael GilliganParticipant @michaelgilligan61133]

I don’t doubt your word for a moment, Alan … but it’s interesting to contemplate how such a mass as Ian’s might be “maintained “

In [for want of a better term] real-life 0.1mg is a very small amount of “stuff”

NPL clearly goes to astonishing lengths … but they are rather special.

If you know … do please enlighten us.

MichaelG.

[Michael Gilligan]

On Michael Gilligan Said:

In [for want of a better term] real-life 0.1mg is a very small amount of “stuff”

[ UPDATE ]

See picture, here:

https://www.murakami-koki.co.jp/en/products/weight/sub_mg/

… noting that the text is more interesting.

MichaelG.

 

[old martParticipant @oldmart]

The NPL in the UK checks master weights for test houses which have to be recertified regularly. That 100g weight should have had a certificate with it when new from its country of origin and should have never been handled without special tools, never fingers. Weights should stay the same wherever they are, but spring balances would be affected by local gravity.

I have one of those cheap electronic 100g scales and got some even cheaper weights which are about +- 50mg which is good enough for my purposes, I think the balance may be better than the weights. If I weigh the weights individually and record the scale readings, and then more than one at once, the scale shows the combined weight within 5mg.

The plus or minus one millionth part was indeed correct at the time the weight was certified. A metrology department would expect to work to that tolerance.

[Michael Gilligan]

On Michael Gilligan Said:

I don’t doubt your word for a moment, Alan … but it’s interesting to contemplate how such a mass as Ian’s might be “maintained “

In [for want of a better term] real-life 0.1mg is a very small amount of “stuff”

NPL clearly goes to astonishing lengths … but they are rather special.

If you know … do please enlighten us.

MichaelG.

Hi MichaelG, I looked for something that weighed 0.1mg, the best thing I could find was a single granule of Silver Spoon sugar, which weighed 0.13mg, most of them were a little over 0.2mg, this was according to my Sartorius R 200 D electronic semi-microbalance. It’s the large white dot, more or less in the centre of this 30mm dia. plastic pan.

Regards Nick.

[not done it yetParticipant @notdoneityet]

That would not be a standard weight.  It would be a standard 100g mass.

Mass and weight are not scientific equivalents.  That 100g mass would only weigh about 30g on the Moon.  Weight depends on the gravitational field in which the mass is located, apart from the example of acceleration towards the Earth for orbiting bodies.

People on the ISS are weightless, but they are nowhere near out of the influence of the Earth.

Space craft under no power travelling towards the Moon continually slow down until the gravitational force provided by the Moon is greater than that of the Earth.  After that point they would then accelerate towards the Moon.

Simple Physics.

[duncan webster 1Participant @duncanwebster1]

People on the ISS are not without weight, the earth still experts a gravitational pull. This pull provides the centripetal force which keeps the astronauts and the ISS in orbit. They appear to be weightless only relative to their immediate surroundings.

[Michael GilliganParticipant @michaelgilligan61133]

A useful domestic ‘quick-reference’ there, Nick

[ although I don’t actually use sugar ]

Thanks

MichaelG.

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