Digital scales

[Bill]

As part of my crusade to clear some of my old junk from the house, I have been using Freecycle and ebay. For the latter I have been having to weigh things to post, so I dug out my old Aldi digital parcel scale, and wanted to check it. When last used about a year ago, I was stung for extra cash in the post office because their scales didn't agree with mine.

Fresh batteries and a wipe down with a clean cloth and I was ready to go, but item weights were all over the place. Reading online made me head for the hard flat(tish) surface of the bathroom floor where my

1litre of Tesco Pineapple juice repeatedly weighed 1070 grams. Bring it back to the carpeted "office" floor and I get a variable measurement with the same juice of around 760grams. The carpet is thin and well worn, but not threadbare, and I wouldn't have expected such a difference.

Searches online reveal a number of contradictory explanations and usually lead to discussions from females stressing about their weight.

Oh, and don't mention Freecycle. My 1U 19" rack case took ages to be approved by the moderators and has just popped up on page 4 of their new listings. Who is going to see it there?

[Richard]

Why the floor, don't you have a table?

[Graham.]

You need a hard flat surface! The carpet is acting like a spring and is sharing the force with the strain gauges in the scale, that's why you get a lower reading.

[alan_m]

In my experience modern light weight scales are only accurate if positioned on a hard flat surface. Both of the scales in my house are seated on top of a thick MDF board. As you have discovered a thin carpet or even vinyl type cushion flooring with a hard foam backing give inaccurate/inconsistent results.

[Bill]

Bad back, and some things are quite heavy. Also, because of family situation, I'm having to do everything upstairs. My office tables are somewhere under "stuff". Hence the need to decrappify.

[Max Demian]

I think it's more likely that the moving part of the scale is pressing against the pile of the carpet, depending on the design of the scale. I don't see how putting the scale on top of a springy thing can "share the force".

[Chris Hogg]

+1

If you stood several sets of scales on top of each other, would the sum of their readings add up to the full applied? I don't think so: each set of scales would read the full load.

[Harry Bloomfield]

I use my bathroom digital scales on a thick bedroom carpet surface, they are quite predictable, apart from when I step on them off centre.

[Tim Watts]

On a related note, I found Freegle to be very good when I used it the other day. Much updated with som every nice features to make posting photos and handling enquiries easier. There was a "promise it to X" option which is nice (it greys it out to let others know someone has dibs) and a "Release my address". Small things but compared to the last time I used Freecycle, saved a lot of messaging.

[Tim Watts]

You might be better with a spring balance (or electronic version thereof). Avoids a lot of the problems of loads that are off centre and scales that are fussy about that.

[Tim Watts]

It's not so much sharing forces (unless the carpet is so thick the box is actually being supported by it) - it's a facet of cheap scales.

The scale box, not being properly supported will twist and the internal mechanism probably only has one sensor with a lever arrangement and relies on a solid base and being level to remain accurate.

Even my medical grade Seca scales demand being levelled (and have a bubble on to assist).

You could construct a set of scales with 3 legs, gauges on each and a top plate that would in theory be accurate on any surface as long as the top plate remains clear of any carpet pile.

But no one does that.

[Andew Jones]

There must be a reason why no one does that.

[Bill]

Just to report back, I have now brought in an old, dense square of wooden flooring tile and put it between the carpet and the scales.

The test reading is now correct, and agrees with the bathroom floor test.

I am still not totally convinced about the theory behind this. The carpet has pretty well no pile at all, and the scales have small support feet that are large enough to keep the bodywork above the pile. I can push paper between the scales and the carpet. I'm also not sure about the scales twisting. I can move them between carpet and smooth surface without reclibrating, and see a reading go from 0 to 400ish grams with nothing on the scales.

Anyway, I now know how to make sensible measurements. Thanks to all.

[alan_m]

Very probably someone does but not at a price point to capture much of the existing domestic market where the accuracy of widely available products is adequate, if used properly.

[Andew Jones]

There is no reason why it costs more and very few of the domestic products even give a reproducible reading, let alone an accurate one.

[Tim Watts]

I was wrong on one count:

It seems, having watched some YT teardown vids, that a lot of cheap modern scales do have 4 load sensors, one on each foot.

So the problem, apart from how accurate the load sensor is, comes down to the carpet pile under the very slim base bypassing the sensors and pressing on say the battery compartment.

All those need, in theory, is longer legs direct to the load sensors and not coupled to the case on the leg side.

[Tim Watts]

The worse thing about cheap bathroom digital scales is that some lie outright. If you get on and it samples Xkg. Step off, and on and you can see it read X-5% for a moment then it suddenly snaps to exactly X. You have to put a dummy lighter load on, or let it turn off and on to get it to actually take a new reading.

[Andew Jones]

It can't be that easy or everyone would be doing it.

[Andew Jones]

Clearly that must be a fudge given how hard it is to get a reproducible reading, let alone an accurate one.

[Tim Watts]

Not necessarily. It's easy to use conduit for all cables runs in walls when building a house. Cost: next to sod all extra. No one does it (well, I did when renovating).

Why? Lazy, cheapskate-ness, "The builder doesn't have to live with fixing it", etc.