Massmeter teardown time.

[SeanB]

Anybody want to see a teardown of a massmeter? I have an Avery Berkel G220 that has been scrapped mechanically, so it is teardown or skip time for it.

ewlectrically it is perfect, cosmetically in good condition but the loadcell is sprained, and has a definite hump in the response, being non monotonic at around 2/3 full scale.

Range is from 0-15kg, plus a little leeway, and resolution is 0.5g.

[M. András]

i would love to see some pics. never seen such a device

[SeanB]

Here it is, turned into a set of parts for recycling.....

[T4P]

Basically a weighing scale ain't it ?

[SeanB]

Yes, but there is the added functions like counting, and the ability to have external devices like printers, added displays and remote pole displays along with a serial interface to a computer.
It has to be unconditionally stable with each reading, even though it does track zero drift it can spend long periods with a mass on the pan, and that reading cannot drift.

[T4P]

Yes, but there is the added functions like counting, and the ability to have external devices like printers, added displays and remote pole displays along with a serial interface to a computer.
It has to be unconditionally stable with each reading, even though it does track zero drift it can spend long periods with a mass on the pan, and that reading cannot drift.

Alright, looks quite plain in my eyes but i assume as a massmeter it doesn't need more then that ... cost i can understand

[muvideo]

Thank you for the images, the machined aluminium block is interesting,
I dont understand in what position the stain gauge was positioned.
Did you try to undestand if the problem was in the strain gauge?

And now a "semantic" question, my english is not that good,
but shouldn't be more appropriate the term "weight meter" ?

At least in my native language Mass measurement is different from
Weight measurement, I was expecting a teardown of some strange
oscillating device

Fabio.

[eevblogfan]

hey ,

based on my knowledg , weight is the relationship between the Gravity and the mass of the object ,

when considering the Gravity on earth is ( 9.8 ) you actually meassures only the mass of the object ( you've "calibrated" the meter to tell you what is the mass if the Gravity is known,

hence calling it massmeter , is more accurate ( unless I'm mistake ofcorse )

have a nice day !

[muvideo]

when considering the Gravity on earth is ( 9.8 ) you actually meassures only the mass of the object ( you've "calibrated" the meter to tell you what is the mass if the Gravity is known,

Yes, you measure the Force (Newton) that exists between the object and the earth,
If I remember correctly there should be devices that measure the inertial mass directly.

If you want an accurate value you have to take in account local gravity acceleration,
dont know by how much, I imagine that the effect can become noticeable on better than 0.1%
accuracy measurements. I imagine that a basic calibration with a known mass will correct for
local gravity, since usually the precision scales will not travel from equator to poles or from
sea level to everest

Fabio.

[SeanB]

Yes, the problem is the strain gauge, but unfortunately this model was discontinued in 2001, and spares are not available. In any case the gauge is not a spare part, it only comes complete with the ADC and micro, precalibrated and linearised. You need a dongle to do that ( the odd edge connector is where it plugs in) and costs more than the unit is worth. A new massmeter was a lot cheaper, and came with a warranty, and , more importantly, a manual so that I can actually do calibration on it without needing a dongle.

Calibration of precision massmeters is always performed in situ, as then the unit can be compensated for the difference in local values of G, which is detectable with this unit ( or rather it was......) if I took it and used the calibrated masspiece in it's usual location, then took it to  nearby town 500m higher in altitude, where it was about 2 counts different.

The strain gauge block is machined to provide a linear response, and as well to provide overload protection, it only moves 0.5mm from no to full load in any case.