Sciencemadness Discussion Board

Will leaving stuff on an electronic balance decalibrate it?

fusso - 9-12-2018 at 08:43

I'd heard that leaving heavy objects on an electronic balance for prolonged durations will decalibrate it. Is it true? If yes, how will it be decalibrated? Will further measurements look lighter or heavier than they should be? Will the decalibrated graph become y=x±k or y=kx (assume balance is calibrated to y=x)?

unionised - 9-12-2018 at 09:36

Time will upset anything, including balances. A long time under heavy load will upset them more.

It's likely that the effect will be that the graph becomes
y=mx+c

But you may be able to calibrate the balance.
Most electronic balances have a zero or tare function- that solves the problem of "c".

And, if you are weighing everything on the same balance, it doesn't matter much if m is not exactly 1.
You can always check it with a known mass.

Fulmen - 9-12-2018 at 14:14

It's quite possible. Any material under strain can creep over time. Structurally it's not a big problem, but you have to factor it in. But in a delicate tool like a scale even small changes in internal stresses can affect it's performance.

Ubya - 9-12-2018 at 16:37

Quote: Originally posted by fusso  
I'd heard that leaving heavy objects on an electronic balance for prolonged durations will decalibrate it. Is it true? If yes, how will it be decalibrated? Will further measurements look lighter or heavier than they should be? Will the decalibrated graph become y=x±k or y=kx (assume balance is calibrated to y=x)?


the load cell could bend over time if stressed continuosly.
if you are using a low resolution balance (1g) it shouldn't be a big problem, but if you are using an analytical balance even looking at it the wrong way could mess with the weighing.
any precision instrument shoul be used carefully and stored safely, don't use your scale as storage space, don't use volumetric flask as boiling flasks etc. just common sense

Quibbler - 11-12-2018 at 06:51

I'm in the process of replacing the electronics in an old electronic balance. I was lucky enough to get a written-off balance from my place of work.
It's proving tricky, but it seems like a good idea as the difficult part (the balancing mechanism) is still good it's just the electronic are old (1980s? 1970s?) and no longer work.
It probably does not help that when plugged (even when it is switched off) the electonics are energised the off switch only switches off the display.

This balances uses an electromagnet to keep the balance pan in the same place as load is applied ( and all other balance I have opened up use the same principle even newer ones -these are ones that go to 2.5 kg and measure to 0.1g I am trying to up mine to 0.01g)
The one I am working on has the electromagnet fully energised when there is no load (it is pulling against a spring) and with big load much less current is supplied to the coils.
The basic principle is that there is a shunt resistor in series with the coils and the voltage acrross this (a measure of the current) is digitized to give the weight reading.
So with a heavy weight the balance is actually doing less work.