On 27 Jan 2004 22:07:09 -0800, (-L.) wrote:

| Dave Fawthrop > wrote in message >. ..
| > On 27 Jan 2004 08:54:22 -0800, (-L.) wrote:
| >
|
| > | Just FYI. The proper way to weigh solids is to add an excess to the
| > | scale and then *remove* the material until you reach the desired
| > | weight.
| >
| > I must disagree with that, it is absolutely forbidden in Chemistry because
| > there putting anything back in the jar may cause contamination. In
| > cooking it must be a bad thing.

| Actually it is the recommended method by most makers of analytical
| balances. That's how they are calibrated.

Very Interesting!
It means that the analytical balance people are well aware of the friction
problems and take steps the minimise them.

In the kitchen where we have a choice between absolute accuracy and
possible contamination of our stocks. For myself I would prefer to avoid
contamination.

Dave F

graham wrote:
>
> > wrote in message
> ...
> > In uk.food+drink.misc Peter Aitken > wrote:
> > > > wrote in message
> > > ...
> > > > In uk.food+drink.misc Fred > wrote:
> > > > >
> > > > > > >
> > > > > >
> > > > > > So, what is the advantage of digital scales over my springy ones?
> > > > > >
> > > > > > --
> > > > > > Adrian
> > > > >
> > > > > Greater accuracy.
> > > > >
> > > > Accuracy of indication maybe but the mechanics of transferring the
> > > > measurement to the electronics are just the same as for any
> > > > 'mechanical' scales.
> > > >
> > > > --
> > > > Chris Green
> > >
> > > I do not believe that is true. The electronic balances that I am
> familiar
> > > with use some sort of solid state pressure transducer that converts the
> > > weight into a voltage. Spring balances use the weight of the food
> against a
> > > spring to move the indicator dial. Very different processes.
> > >
> > How about balance type mechanical scales, very accurate and very easy
> > to zero set correctly.
>
> I have some balance scales but what with parallax etc., it's difficult to
> see when the pointer is exactly at the mark (at least on mine). I use my
> Salter electronic all the time now and I always press the scale after adding
> the last couple of grams to make certain that the reading is OK. From what
> has been said here, I think that I might have to invest in some weights to
> check their accuracy.
> My only complaint is the cost of the batteries and, to me, their relatively
> short life-span.
> Graham

I have a Soehnle digit scale made in Switzerland I bought at the
Canadian Tire chain store for about CDN $50. I couldn't figure out how
the sale took readings until I just read in this news group how it is
done. Easy switch from pounds to grams. Had it about a month so don't
know the battery usage pattern but easily wired to wall outlet if
battery life is short. I have been looking for years for an affordable
digital scale. This is it. While it has a million uses, I particularly
like the ability to pour the flour for my bread machine recipes onto the
scale without having to tap the flour to settle it for measure.

The scale is a good teaching tool, too. After you have weighted out
something like chicken breasts portions a few times, you can almost
cut "meat" up perfectly to a specific weight accuracy checking randomly.

"occupant" > wrote in message
...
> graham wrote:
> >
> > My only complaint is the cost of the batteries and, to me, their
relatively
> > short life-span.
> > Graham
>
> I have a Soehnle digit scale made in Switzerland I bought at the
> Canadian Tire chain store for about CDN $50.

I'll take a look at these this w/e. By then, the daytime temperature is
forecast to be above -30ºC :-((

Graham

Dave Fawthrop > wrote in message >. ..
> On 27 Jan 2004 22:07:09 -0800, (-L.) wrote:
>
> | Dave Fawthrop > wrote in message >. ..
> | > On 27 Jan 2004 08:54:22 -0800, (-L.) wrote:
> | >
>
> | > | Just FYI. The proper way to weigh solids is to add an excess to the
> | > | scale and then *remove* the material until you reach the desired
> | > | weight.
> | >
> | > I must disagree with that, it is absolutely forbidden in Chemistry because
> | > there putting anything back in the jar may cause contamination. In
> | > cooking it must be a bad thing.
>
> | Actually it is the recommended method by most makers of analytical
> | balances. That's how they are calibrated.
>
> Very Interesting!
> It means that the analytical balance people are well aware of the friction
> problems and take steps the minimise them.
>
> In the kitchen where we have a choice between absolute accuracy and
> possible contamination of our stocks. For myself I would prefer to avoid
> contamination.
>
> Dave F

It probably depends on what it is. I don't think re-introducing
staples like sugar or flour is an issue. Anything with poterntial
quick spoilage may be an issue, though.

-L.

In article >, Dave Fawthrop
> wrote:

> Very Interesting!
> It means that the analytical balance people are well aware of the friction
> problems and take steps the minimise them.

> Dave F

I work in laboratory and routinely use numerous electronic balances whose
accuracy range from 0.01 gram to 0.00001 gram. We do not see any of the
problems use describe. I do not think this is a design feature of
electronic balances in general. Our balances cost many thousands of
dollars.

I have a cheap electronic balance at home that is more temperamental
(does not tare more than once) but probably cost less than $50-100.

Roland

On 25/01/2004 at 16:27:49, Farry typed:

> Dave Fawthrop > wrote:
>
> > Judder!
> > A well known mechanical engineering problem. Often experianced in
> > car brakes when the car vibrates when braking.
> > Friction varies with position and time, not like they teach you in
> > school. I have seen it in lots of things but never in scales.
> >
> > Take it back and demonstrate the problem, Even a shop assistant
> > should understand that it does not work properly. Get a
> > different model, it may be a batch problem.
>
> I can't take it back to the shop, because I bought the original a year
> ago, and now I've just got a replacement under guarantee by post from
> Salter. So I'll wait for the response from Salter to my query, first.
>
> I appreciate that it's hard to believe that this behaviour could be
> designed in. OK, next experiment.
>
> I repeat the process of adding muesli to the bowl three times, without
> zeroing the scale, and weigh the bowl each time. It starts at 274g,
> then it's 254g, then 236g, then 216g. i.e. 18-20g down each time
> leaving it 58g low. And since I completely remove the bowl from the
> scale to tip out the muesli each time, that should have sorted out
> any judder.

How about an experiment in which something is added *really* slowly but
over a long period of time such that the final amount of the item is
significant enough that you can rule out judder? I'm originally
thought of water dripping at a set rate but of course evaporation will
skew the results. Maybe a slowly dispensed powder?

--
Abso [at] ukrm [dot] net - Ignore header email address

The uk.people.consumers.ebay FAQ is at www.upce.org.uk

In order to maintain secrecy, this posting will self-destruct
in five seconds. Memorize it, then eat your computer.

"Abso" > wrote:

>How about an experiment in which something is added *really* slowly but
>over a long period of time such that the final amount of the item is
>significant enough that you can rule out judder? I'm originally
>thought of water dripping at a set rate but of course evaporation will
>skew the results. Maybe a slowly dispensed powder?

The trouble with that is that the display times out after 2 minutes. I
think that I've shown that the shift is too consistent for judder. (See
the post about shifting the zero point.)

--
Farry

Adrian Tupper > wrote:

>Dave Fawthrop > wrote in
:
>
>> On 27 Jan 2004 08:54:22 -0800, (-L.) wrote:
>>
>>| Just FYI. The proper way to weigh solids is to add an excess to the
>>| scale and then *remove* the material until you reach the desired
>>| weight.
>>
>> I must disagree with that, it is absolutely forbidden in Chemistry
>> because there putting anything back in the jar may cause
>> contamination. In cooking it must be a bad thing.
>
>Nearly everything weighed in this manner is dry and I wouldn't hesitate
>putting sugar, raisins or even butter back in the packet.

I've found that I'm 10 times more likely to spill something trying to
put it back in the packet, compared with transferring it to a bowl. If
it's an ingredient that comes in a cardboard box with a plastic liner,
then the powder can get dropped between the two where it will spoil, and
if I later tip the packet into the bowl then out comes the spoiled
powder.

--
Farry

On Thu, 29 Jan 2004 11:56:57 GMT, Farry
> wrote:

| "Abso" > wrote:
|
| >How about an experiment in which something is added *really* slowly but
| >over a long period of time such that the final amount of the item is
| >significant enough that you can rule out judder? I'm originally
| >thought of water dripping at a set rate but of course evaporation will
| >skew the results. Maybe a slowly dispensed powder?
|
| The trouble with that is that the display times out after 2 minutes. I
| think that I've shown that the shift is too consistent for judder. (See
| the post about shifting the zero point.)

Did you fail to use the 10 year Guarantee which the Salter web site
advertises for your particular scale? Are there hidden problems in this
guarantee? At worst you should be able to get your money back or get it
replaced with a different product.

Dave F

I was down the pub last night, boring my friends with the Salter kitchen
scale problem, and one of them mentioned that he had a Salter bathroom
scale. He said that if he weighed himself twice with a gap of about 1
hour between weighings, then the scale would show almost 1kG difference
(that's 2.2lbs for American readers). We asked if he might have done
anything in between that might have altered his weight, but he insisted
not. That seems worse than the consistency of mechanical bathroom
scales.

--
Farry

Dave Fawthrop > wrote:

>Did you fail to use the 10 year Guarantee which the Salter web site
>advertises for your particular scale? Are there hidden problems in this
>guarantee? At worst you should be able to get your money back or get it
>replaced with a different product.

I did use the 10 year guarantee to get the current scale. I sent a
feedback form message to Salter enquiring if they had any scales without
this problem, but they've not replied yet. It's a bit pointless asking
for a replacement, and risking losing the scale in the post, if it's
going to be the same. I hesitate to phone them because the chances of
one of their customer support people knowing about the problem is zero.
If they don't reply in within a few days, I'll consider phoning them
anyway.

--
Farry

"Farry" > wrote in message
...
> I was down the pub last night, boring my friends with the Salter kitchen
> scale problem, and one of them mentioned that he had a Salter bathroom
> scale. He said that if he weighed himself twice with a gap of about 1
> hour between weighings, then the scale would show almost 1kG difference
> (that's 2.2lbs for American readers). We asked if he might have done
> anything in between that might have altered his weight, but he insisted
> not. That seems worse than the consistency of mechanical bathroom
> scales.
>
> --
> Farry

I think 'just under 1kg change' in an hour is neither here nor there ..... a
pint of beer is just over 1/2 kg, having a good slash will loose 1/2 kg, a
good doohdah could be 1 kg, removing shoes, taking money out of pocket ....
even a cup of tea will account for 1/3 kg .... PLUS you can get that sort of
change if your C of G changes, ie try leaning forwards or backwards while
standing on the scale and see the effect!

Dave

I've had a look at the Salter electronic bathroom scale that I mentioned
yesterday, and it's behaviour is even more surprising than the Salter
electronic kitchen scale.

This scale belongs to a friend of mine who showed me how it works. You
tap it with your foot to wake it up and wait for it to zero, then you
stand on it, and after a few moments it works out your weight and
displays that on an LCD. You can't then change that be shifting your
weight because the display remains fixed until you step right off it.
The display has a 0.1kG resolution.

My friend demonstrated that the scale was very consistent from one
moment to the next by stepping on it several times, and each time the
displayed weight was exactly the same. He then said that if we waited
for a period before stepping on it then the display would show a
different weight; he wasn't sure how long, exactly. This demonstration
took a surprising turn when his wife weighed herself on the scale, and
then he weighed himself again, and then the display showed 0.7kG
difference from his previous weight.

After a lot of experimenting, we worked out what was going on. In actual
fact, the scale was less consistent than most mechanical bathroom
scales. The displayed weight varied over a range of about 1kG despite
having a display resolution of 0.1kG. However this inconsistency is
hidden by a filter in the electronics.

The scale tries to work out if the person that had stepped on the scale
previously was stepping on the scale again, and will then display
exactly the same weight. It does this by remembering the previous
person's weight, and if the weight of the next person to stand on the
scale seems to differ by less than about 1kG, then it's probably the
same person, so it displays exactly the same weight as previously. You
can defeat this simply by having somebody else stand on the scale for a
moment so that the scale forgets the previous person's weight.

We probed this behaviour by stepping on the scale, noting the display,
and then stepping on the scale again while holding a weight in the hand,
and found that if the weight that we held was less than ~1kG, then the
displayed weight would be the same as before, but if it was greater than
~1kG, the displayed weight would change. The exact threshold weight was
a bit difficult to determine because of the inconsistency. We knew that
the scale would eventually forget the stored weight, if we waited long
enough, but we haven't worked out how long.

Presumably, the whole idea of this is to prevent the consumer from
discovering how inconsistent the Salter electronic bathroom scales are.
If people immediately discovered that the expensive scale that they'd
bought was less consistent than a mechanical scale, they might take it
straight back to the shop. Also, anybody doing a review of the scale for
a publication would probably think to check how consistent the scale
was, but they'd probably not discover the stored weight trick in the
time they had available.

I'm tempted to have a word with Trading Standards to see what they think
about this.

--
Farry

David Wilkinson > wrote in message >...
> Mark Willstatter wrote:
> >The other possibilities that have
> > been mentioned - software, strain gauge/gage, a/d conversion, and so
> > on, are unlikely to vary with time. In other words, I'm with Dave.
>
> But the removal and replacement of the bowl (a large sudden change,
> which should overcome any inherent "stickiness") clearly demonstrates
> that the bowl has "lost weight". i.e. the scales have changed their
> concept of the "zero point".
>
> It would be interested to see if the experiment could be repeated a
> number of times until the weight of the bowl registered "zero".
>
> Based on the evidence to date, I could well believe that the scales are
> adjusting their "zero point" over time.
>
> Dave W.

Mea culpa - it was a case of me reading what I wanted to read, not
what was written. I was just *sure* there was a re-zero in there
somewhere ;^) So let me propose and alternate explanation, one that
has been suggested before although not in quite the same way:
software. The only way I can expain this is if the designers of this
instrument felt they needed to compensate for possible drift - in the
strain gauge bridge circuit, amplifier, A/D converter, wherever. IOW,
they knew users would be disconcerted about watching the displayed
weight change by itself as the electronics drifted and so included
provisions in the software to distinguish between slow changes that
would presumably be drift and fast changes that would presumably be
caused by weight being added or removed by a human. When the weight
was added very slowly, it was interpreted as drift and so the zero
was, in fact, changed. How's that sound? My advice: don't do that!
Congratulate yourself on having successfully simulating electronic
drift in this experiment. If I'm right (a big "if", I'll grant you)
then the scale will be fine in normal use.

- Mark W.

(Mark Willstatter) wrote:

>Mea culpa - it was a case of me reading what I wanted to read, not
>what was written. I was just *sure* there was a re-zero in there
>somewhere ;^) So let me propose and alternate explanation, one that
>has been suggested before although not in quite the same way:
>software. The only way I can expain this is if the designers of this
>instrument felt they needed to compensate for possible drift - in the
>strain gauge bridge circuit, amplifier, A/D converter, wherever. IOW,
>they knew users would be disconcerted about watching the displayed
>weight change by itself as the electronics drifted and so included
>provisions in the software to distinguish between slow changes that
>would presumably be drift and fast changes that would presumably be
>caused by weight being added or removed by a human. When the weight
>was added very slowly, it was interpreted as drift and so the zero
>was, in fact, changed. How's that sound? My advice: don't do that!
>Congratulate yourself on having successfully simulating electronic
>drift in this experiment. If I'm right (a big "if", I'll grant you)
>then the scale will be fine in normal use.

I guess you missed the first post in this thread:

http://groups.google.com/groups?thre...d1% 404ax.com

--
Farry

Farry > wrote in message >. ..
> (Mark Willstatter) wrote:
>
> >Mea culpa - it was a case of me reading what I wanted to read, not
> >what was written. I was just *sure* there was a re-zero in there
> >somewhere ;^) So let me propose and alternate explanation, one that
> >has been suggested before although not in quite the same way:
> >software. The only way I can expain this is if the designers of this
> >instrument felt they needed to compensate for possible drift - in the
> >strain gauge bridge circuit, amplifier, A/D converter, wherever. IOW,
> >they knew users would be disconcerted about watching the displayed
> >weight change by itself as the electronics drifted and so included
> >provisions in the software to distinguish between slow changes that
> >would presumably be drift and fast changes that would presumably be
> >caused by weight being added or removed by a human. When the weight
> >was added very slowly, it was interpreted as drift and so the zero
> >was, in fact, changed. How's that sound? My advice: don't do that!
> >Congratulate yourself on having successfully simulating electronic
> >drift in this experiment. If I'm right (a big "if", I'll grant you)
> >then the scale will be fine in normal use.
>
> I guess you missed the first post in this thread:
>
> http://groups.google.com/groups?thre...d1% 404ax.com

Actually, I didn't - but it's been so long, I forgot! So I guess we
wasted a lot of time here. What's the problem?

Farry > writes:

>If people immediately discovered that the expensive scale that they'd
>bought was less consistent than a mechanical scale, they might take it
>straight back to the shop.

I don't know what's "expensive" for a scale, so I took a quick
look at an industrial catalog. It shows small mechanical scales
for $80, electronic scales for $200, and "counting scales" (which
require high repeatability for counting parts) for $900.

It would be interesting to know what the difference is between
the $200 scale and the $900 scale. Do these scales have any
moving parts, or is it all in the electronics?