magnetic field

[R. Steve Walz]

Lory wrote:

Hi,

The sine waves in my XR2206 IC function generator started
at 3 volts and varied from there to 5 volts and 1 volt.

In ordinary function generator equipment. Is the
sine wave at 0 volts and rising/falling from it or
does it also start at higher voltage as base?

Lory
-----------

Put it through an inline capacitor and it will be referenced to 0
as long as it is a sine and is buffered by an amp after it. Then
you can add an op-amp adder stage to add any DC offset to it that
you wish.

-Steve
--
-Steve Walz rstevew@armory.com ftp://ftp.armory.com/pub/user/rstevew
Electronics Site!! 1000's of Files and Dirs!! With Schematics Galore!!
http://www.armory.com/~rstevew or http://www.armory.com/~rstevew/Public

 

[R. Steve Walz]

Lory wrote:

A wire carrying DC has static field.. similar to the one
in bar magnets. How come when you put two parallel wires
together in the DC circuit. The magnetic field cancels
while in a bar magnet, it doesn't. If you do proper
positioning of 2 bar magnets, do you think you can cancel
the magnetic field from bar magnets? why and why not?
If not, why can the magnetic field in DC carrying wire
be canceled while in magnets it can't.
Lory
---------------------------

The bar magnet has a field that varies due to the positions of all
its iron atoms acting as tiny magnets. Its field can only be canceled
locally to specific points where it is numerically zero. Since this
field varies according to where along the magnet you are and where
in space, it is not generally cancelable. The field around a wire
is much more symmetrical and you can get them quite close together.
Also an individual wire's field will be much smaller in intensity.

-Steve
--
-Steve Walz rstevew@armory.com ftp://ftp.armory.com/pub/user/rstevew
Electronics Site!! 1000's of Files and Dirs!! With Schematics Galore!!
http://www.armory.com/~rstevew or http://www.armory.com/~rstevew/Public

 

[Yukio YANO]

siliconmike wrote:

I would appreciate if anyone can advise as to how to make magnets. I
have an electronic engineering background, but have never done this
before. I want to make tiny magnets, say size of 4mm x 4mm or 6mm x
6mm, of the power of 4000 to 5000 Gauss (higher the better)..

What material should I use ?
What coating should I do on that material for corrosion protection ?
What would be the thickness of the coating ?
Should I do coating before / after magnetizing ?
What would be the coil / dc power setup ?
How do I measure the strength afterwards ?

Any advise would be great.

Thanks
Mike

My wife buys 4mm R/E magnetic clasps for her Bead work. Don't know
strength but sure beats the older styles for grip. Test by loading the
clasp and note total weight required to uncouple the clasp.

Yukio YANO

 

[Tomi Holger Engdahl]

John Fields <jfields@austininstruments.com> writes:

On 26 May 2005 11:14:22 +0300, Tomi Holger Engdahl
then@solarflare.cs.hut.fi> wrote:

"Lory" <lorrainewinters80@yahoo.com> writes:

Hi,

How do you calculate the output voltage of a particular power
amplifier model? They are most rated in watts such as
750W @ 4 ohm load.

The power to a load can be calculated with voltage
and resitance values with equation

power = (U * U) / R

Where U is the voltage and R is the resistance

---
Since when is voltage "U"?

Dependign on what books or other references you read you can
see letters U, E and V used to mark voltage on the equations.




--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/

 

[Jonathan Kirwan]

On 27 May 2005 00:18:42 -0700, "Nikolas Britton"
<nbritton@nbritton.org> wrote:

snip
Find some dead hard drives and pull the magnets from them. I don't know
what kind they are but they are very powerful, keep them very far way
from credit cards... I found that out the hard way! Hold them up into a
fluorescence light ballast, they will easily pick up the 60Hz hum and
quiver in your hand like theres no tomorrow.

The motors in the drives are rather powerful too...

Reasonable advice. I haven't pulled any from hard drives, but I have
pulled them from old (dead) CD-ROM drive heads. And they are pretty
nice! About .22" x .29" x .12" in size. And very strong.

Jon

 

[Impmon]

On 27 May 2005 00:18:42 -0700, "Nikolas Britton"
<nbritton@nbritton.org> wrote:

Find some dead hard drives and pull the magnets from them. I don't know
what kind they are but they are very powerful, keep them very far way
from credit cards... I found that out the hard way! Hold them up into a
fluorescence light ballast, they will easily pick up the 60Hz hum and
quiver in your hand like theres no tomorrow.

I got a few out of old 5.25" full height drives. First time I let the
2 pieces get close together with my finger in between, I had black and
blue bruise for several days. Bring it within a foot of CRT (TV or
monitor, doesn't matter as long as it is CRT) and you get
multi-colored lava lamp impression.
--
When you hear the toilet flush, and hear the words "uh oh", it's already
too late. - by anonymous Mother in Austin, TX
To reply, replace digi.mon with phreaker.net

 

[CWatters]

"Nikolas Britton" <nbritton@nbritton.org> wrote in message
news:1117178322.106605.66500@g14g2000cwa.googlegroups.com...

The motors in the drives are rather powerful too...

Model flyers rewind them and use them to fly small RC model planes.

 

[CWatters]

"Lory" <lorrainewinters80@yahoo.com> wrote in message
news:1117146922.950761.147240@f14g2000cwb.googlegroups.com...

Hi,

Does ordinary DC power supply produce ripples?

Lots of info here...
http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/audio/part5/page1.html

How come the dc power supply didn't use
this eliminator,

Some circuits can tollerate the ripple.

.. is it expensive?

That depends on the size (in Watts) of the power supply.

The regulator in some plug style mains adaptors is usually quite cheap. Lets
call it less than $1 - but even $1 is expensive if you are selling 1,000,000
a year.

 

[GaryG]

<john.ruckstuhl@gmail.com> wrote in message
news:1117240503.036397.58190@g14g2000cwa.googlegroups.com...

Sneaky scales fudge weights deliberately.

I suspect that many modern, microprocessor -controlled bathroom scales
have programmed in hysteresis to increase user confidence in the
scale's accuracy. The scale remembers fresh measurements, say 166.2#,
and if it next measures same weight +/- a little (within a short time),
say 166.8#, then the scale decides to report the *original* measurement
166.2#. Neat. Sneaky. User believes the scale is highly repeatable.

On such a scale, I weigh myself multiple times and get the same reading
(to the 0.2#) each time. 166.2#, 166.2#, 166.2#, 166.2#, ...
Then I weigh something different (myself holding a load), to reset the
memory.
Then I weigh myself again... Now, get something like 166.8#, 166.8#,
166.8#, 166.8#, ... very solid again, but 0.6# different from 1st
series of measurements.

I tried 6 models (2 or 3 brands) at a retail store display and find
this "feature" common.

What models/brands? I find it hard to believe that the manufacturers would
do that, because it would require additional programming in the scale, and
most modern scales are quite accurate as is.

FWIW, I have a 4 year old Tanita, accurate to 0.2 lb, and I've tested it
like you suggest on a number of occasions. In all such tests, (weigh in,
weigh-in holding a light weight of some sort, then weigh in again) the scale
returns to within 0.2 lb of the original reading, and usually to the exact
original reading.

If I step off, reset, and step back on (without changing anything), I get
the same reading about 65% of the time. The other 35%, it varies by 0.2
lb - I assume this is when my actual weight is somewhere between the two
reported weights.

Perhaps your test was flawed somehow? Or, maybe you were testing some
crappy scales?

--
GG
http://www.WeightWare.com
Computer-Assisted Weight Management

Is it important? Maybe yes in the following scenario -- in some sports
like wrestling, boxing, judo, you have multiple competitors weighing in
at the same time, same scale, with possibly very similar weight. Some
competitors are concerned with as little as 0.25#. In this case it
seems one competitor could inherit the weight measurement of the person
in front of him.

In a perfect world, competition weigh-in equipment should be
certified/calibrated. But since the bathroom scale appears so
repeatable, some competitions now use modern, microprocessor
-controlled bathroom scales.

Somebody's going to say... "you shouldn't do that". Right, I agree.
But (a) it's happening, because (b) this hysteresis (memory)phenomenon
isn't widely known, I suspect.

Anyone care to confirm? Contradict? Repeat the experiment on their
own scale? Comment? In my experiment I didn't bother to determine
what weight difference resets the memory -- 1#? 1.5#?

Regards,
John Ruckstuhl

 

[Uncle Al]

john.ruckstuhl@gmail.com wrote:

Sneaky scales fudge weights deliberately.

I suspect that many modern, microprocessor -controlled bathroom scales
have programmed in hysteresis to increase user confidence in the
scale's accuracy. The scale remembers fresh measurements, say 166.2#,
and if it next measures same weight +/- a little (within a short time),
say 166.8#, then the scale decides to report the *original* measurement
166.2#. Neat. Sneaky. User believes the scale is highly repeatable.
[snip]

The reproducibilty of an electronic bathroom scale depends on the
surface underneath. If it is stone or rigidly laid hardwood you'll
get good precision. If it is soft like linoleum or carpet, you
won't. Any need for true precision weighing cannot be satisfied by a
cheap consumer scale.

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf

 

[Luhan Monat]

john.ruckstuhl@gmail.com wrote:

Sneaky scales fudge weights deliberately.

I suspect that many modern, microprocessor -controlled bathroom scales
have programmed in hysteresis to increase user confidence in the
scale's accuracy. The scale remembers fresh measurements, say 166.2#,
and if it next measures same weight +/- a little (within a short time),
say 166.8#, then the scale decides to report the *original* measurement
166.2#. Neat. Sneaky. User believes the scale is highly repeatable.

On such a scale, I weigh myself multiple times and get the same reading
(to the 0.2#) each time. 166.2#, 166.2#, 166.2#, 166.2#, ...
Then I weigh something different (myself holding a load), to reset the
memory.
Then I weigh myself again... Now, get something like 166.8#, 166.8#,
166.8#, 166.8#, ... very solid again, but 0.6# different from 1st
series of measurements.

I tried 6 models (2 or 3 brands) at a retail store display and find
this "feature" common.

Is it important? Maybe yes in the following scenario -- in some sports
like wrestling, boxing, judo, you have multiple competitors weighing in
at the same time, same scale, with possibly very similar weight. Some
competitors are concerned with as little as 0.25#. In this case it
seems one competitor could inherit the weight measurement of the person
in front of him.

In a perfect world, competition weigh-in equipment should be
certified/calibrated. But since the bathroom scale appears so
repeatable, some competitions now use modern, microprocessor
-controlled bathroom scales.

Somebody's going to say... "you shouldn't do that". Right, I agree.
But (a) it's happening, because (b) this hysteresis (memory)phenomenon
isn't widely known, I suspect.

Anyone care to confirm? Contradict? Repeat the experiment on their
own scale? Comment? In my experiment I didn't bother to determine
what weight difference resets the memory -- 1#? 1.5#?

Regards,
John Ruckstuhl

Exactly the same experience I had with a digital scale. It worked out
to a 5 pound window - I dont know the time window. Showed weight to
within 0.5 pound as I got on and off with increasing hand-held weights
until about 5 extra pounds.

I still have it, plan to rework the electronics with a loud voice output
and leave it in the bathroom to catch unsuspecting house guests....

"Ow, oooh, get the heck off me!"

--
Luhan Monat: luhanis(at)yahoo(dot)com
http://members.cox.net/berniekm
"Any sufficiently advanced magick is
indistinguishable from technology."

 

[Robert Baer]

john.ruckstuhl@gmail.com wrote:

Sneaky scales fudge weights deliberately.

I suspect that many modern, microprocessor -controlled bathroom scales
have programmed in hysteresis to increase user confidence in the
scale's accuracy. The scale remembers fresh measurements, say 166.2#,
and if it next measures same weight +/- a little (within a short time),
say 166.8#, then the scale decides to report the *original* measurement
166.2#. Neat. Sneaky. User believes the scale is highly repeatable.

On such a scale, I weigh myself multiple times and get the same reading
(to the 0.2#) each time. 166.2#, 166.2#, 166.2#, 166.2#, ...
Then I weigh something different (myself holding a load), to reset the
memory.
Then I weigh myself again... Now, get something like 166.8#, 166.8#,
166.8#, 166.8#, ... very solid again, but 0.6# different from 1st
series of measurements.

I tried 6 models (2 or 3 brands) at a retail store display and find
this "feature" common.

Is it important? Maybe yes in the following scenario -- in some sports
like wrestling, boxing, judo, you have multiple competitors weighing in
at the same time, same scale, with possibly very similar weight. Some
competitors are concerned with as little as 0.25#. In this case it
seems one competitor could inherit the weight measurement of the person
in front of him.

In a perfect world, competition weigh-in equipment should be
certified/calibrated. But since the bathroom scale appears so
repeatable, some competitions now use modern, microprocessor
-controlled bathroom scales.

Somebody's going to say... "you shouldn't do that". Right, I agree.
But (a) it's happening, because (b) this hysteresis (memory)phenomenon
isn't widely known, I suspect.

Anyone care to confirm? Contradict? Repeat the experiment on their
own scale? Comment? In my experiment I didn't bother to determine
what weight difference resets the memory -- 1#? 1.5#?

Regards,
John Ruckstuhl

Bathroom scales have historically been rather (to be polite) inaccurate.

Notice in a grocery that the scales are all spring scales (ie:
inexpensive) and are marked "NOT FOR TRADE" or "NOT LEGAL FOR TRADE".
They all read *approximate* values, and if not calibrated, can be off
by 20 percent of full scale (either way) for starters.
If you want more reliable or accurate readings, use a balance type of
scale: Toledo comes to mind, Cenco comes to mind; there are others.

 

[CWatters]

<master_gg@yahoo.com> wrote in message
news:1117289664.167933.234090@g49g2000cwa.googlegroups.com...

I am splicing a switch into a wire in that sends pulsed speed signals
in my car. I used AWG 24 telephone wire, solid core. Since cars
vibrate, I used 2 wire conductors for each end of the switch.

I don't think using two wires will help avoid a failure.

Would I be better off re-wiring using a single stranded wire rather
than 2 solid wires?

That would be my choice.

Any issues in using 2 wires in each direction?

Not that I can think of at the low frequencies you are talking about.

Should I worry about any signal loss issues?

Probably not for low frequencies you are talking about.

 

[Rich Grise]

On Sat, 28 May 2005 08:38:23 -0600, JS2 wrote:

"Robert Baer" <robertbaer@earthlink.net> wrote in message
news:ndYle.1270$s64.431@newsread1.news.pas.earthlink.net...
john.ruckstuhl@gmail.com wrote:


Bathroom scales have historically been rather (to be polite) inaccurate.
Notice in a grocery that the scales are all spring scales (ie:
inexpensive) and are marked "NOT FOR TRADE" or "NOT LEGAL FOR TRADE".
They all read *approximate* values, and if not calibrated, can be off by
20 percent of full scale (either way) for starters.
If you want more reliable or accurate readings, use a balance type of
scale: Toledo comes to mind, Cenco comes to mind; there are others.

I've noticed with balance scales that the weight shifts by several pounds
depending upon where you stand on it ... I assume you're supposed
to stand more or less in the center, an inch one way or another can
make a difference of a pound or two (important if you're doing a
sport with weight divisions).

Not only have I never heard of such a thing, I've seen the workings

of scales that go to great lengths to avoid just that. If your scale
shows different weights when the object is on different places on
the platform, then you have been robbed.

Cheers!
Rich

 

[Rich Grise]

On Sat, 28 May 2005 11:03:18 -0700, Quantum Mirror wrote:

"I've noticed with balance scales that the weight shifts by several
pounds
depending upon where you stand on it ... I assume you're supposed
to stand more or less in the center, an inch one way or another can
make a difference of a pound or two (important if you're doing a
sport with weight divisions)."

This would be the incentive to repeat the last reading. This would make
the electronic scale seem more dependable, stop customers from worrying
about water weight gains and losses. It would take a very small amount
of digital memory and programing. I am sure there is even memory for
two or three "normal weights". There is probably a mass produced chip
that includes this program and you will need to find one with a
different chip to change the repeat. I bet you even paid extra for the
"added accuracy"!

Now this is just plain silly. Who in their right mind would go to
such great lengths, just to produce a reading that isn't even what
the weight on the platform is?

The phenomenon that the OP, John Ruckstuhl, mentioned:
"On such a scale, I weigh myself multiple times and get the same reading
(to the 0.2#) each time. 166.2#, 166.2#, 166.2#, 166.2#, ... Then I
weigh something different (myself holding a load), to reset the memory.
Then I weigh myself again... Now, get something like 166.8#, 166.8#, 166.8#,
166.8#, ... very solid again, but 0.6# different from 1st series of
measurements."

Is from hysteresis. He steps on the transducer, it's been sitting all
day stabilizing, so it reads low. He steps on the scale holding weights,
It shows his 166.2 + the weight + some unknown error. He steps off
the scale, and it springs back to something greater than zero; the
scale waits until it's done bouncing, re-zeros itself, and now when
he steps back on it's biased high. The effect would probably be even
worse if he just stayed standing there and set the weight down.

The point being that the sensor takes a "set." And, probably not
so much these days with little strain gauges, but with mechanical
scales, there's sticktion to deal with.

Cheers!
Rich

 

[JS2]

"Rich Grise" <richgrise@example.net> wrote in message
newsan.2005.05.28.18.28.06.428155@example.net...

On Sat, 28 May 2005 08:38:23 -0600, JS2 wrote:


"Robert Baer" <robertbaer@earthlink.net> wrote in message
news:ndYle.1270$s64.431@newsread1.news.pas.earthlink.net...
john.ruckstuhl@gmail.com wrote:


Bathroom scales have historically been rather (to be polite)
inaccurate.
Notice in a grocery that the scales are all spring scales (ie:
inexpensive) and are marked "NOT FOR TRADE" or "NOT LEGAL FOR TRADE".
They all read *approximate* values, and if not calibrated, can be off
by
20 percent of full scale (either way) for starters.
If you want more reliable or accurate readings, use a balance type of
scale: Toledo comes to mind, Cenco comes to mind; there are others.

I've noticed with balance scales that the weight shifts by several pounds
depending upon where you stand on it ... I assume you're supposed
to stand more or less in the center, an inch one way or another can
make a difference of a pound or two (important if you're doing a
sport with weight divisions).

Not only have I never heard of such a thing, I've seen the workings
of scales that go to great lengths to avoid just that. If your scale
shows different weights when the object is on different places on
the platform, then you have been robbed.

I've seen it on doctor's scales, and the typical scale (lever arm with
weights) used in most gyms (don't have any kind of scale at home),
and hence in wrestling and judo competitions. Maybe they're just
old scales so some internal mechanism is worn out, but it seems to
be very common. Not an issue if you're looking to measure your
weight accurately (just stand at the center), but something that can
be used to your advantage (or disadvantage) if you're making
weight division and even a half pound makes or breaks you. My
thought was that if the scale isn't designed properly, it might change
the action point on the lever arm (even .5% change is good for a
pound if you're about 200 lbs).

-JS2

 

[Luhan Monat]

Rich Grise wrote:

On Sat, 28 May 2005 08:38:23 -0600, JS2 wrote:


"Robert Baer" <robertbaer@earthlink.net> wrote in message
news:ndYle.1270$s64.431@newsread1.news.pas.earthlink.net...

john.ruckstuhl@gmail.com wrote:


Bathroom scales have historically been rather (to be polite) inaccurate.
Notice in a grocery that the scales are all spring scales (ie:
inexpensive) and are marked "NOT FOR TRADE" or "NOT LEGAL FOR TRADE".
They all read *approximate* values, and if not calibrated, can be off by
20 percent of full scale (either way) for starters.
If you want more reliable or accurate readings, use a balance type of
scale: Toledo comes to mind, Cenco comes to mind; there are others.

I've noticed with balance scales that the weight shifts by several pounds
depending upon where you stand on it ... I assume you're supposed
to stand more or less in the center, an inch one way or another can
make a difference of a pound or two (important if you're doing a
sport with weight divisions).


Not only have I never heard of such a thing, I've seen the workings
of scales that go to great lengths to avoid just that. If your scale
shows different weights when the object is on different places on
the platform, then you have been robbed.

Cheers!
Rich


This would not explain my experience, just picking up a little extra

weight each time and getting back on the scale. It just would not move
until about 5 pounds total had been added. Only explanation I have is
that is it 'faking' the accuracy; and doing it quite intentionally.

That's why is on my list of projects for re-engineering. Maybe Mavin's
voice "You standing on my like that is just so Depressing!"


--
Luhan Monat: luhanis(at)yahoo(dot)com
http://members.cox.net/berniekm
"Any sufficiently advanced magick is
indistinguishable from technology."

 

[ck]

"JS2" <js2@spam.is.evil.com> wrote in message
news:119h0j32ffvmoe4@corp.supernews.com...

"Robert Baer" <robertbaer@earthlink.net> wrote in message
news:ndYle.1270$s64.431@newsread1.news.pas.earthlink.net...
john.ruckstuhl@gmail.com wrote:


Bathroom scales have historically been rather (to be polite)
inaccurate.
Notice in a grocery that the scales are all spring scales (ie:
inexpensive) and are marked "NOT FOR TRADE" or "NOT LEGAL FOR TRADE".
They all read *approximate* values, and if not calibrated, can be off
by 20 percent of full scale (either way) for starters.
If you want more reliable or accurate readings, use a balance type of
scale: Toledo comes to mind, Cenco comes to mind; there are others.

I've noticed with balance scales that the weight shifts by several pounds
depending upon where you stand on it ... I assume you're supposed
to stand more or less in the center, an inch one way or another can
make a difference of a pound or two (important if you're doing a
sport with weight divisions).

-JS2

A properly designed and calibrated scale should not exhibit this behavior.
Calibrations should be performed according to NIST Handbook 44, which
includes a shift test, a return to zero (testing mechanical hysteresis), an
increasing load test and others depending on the type of scale.

Also, ISO 17025 for calibration labs require all as found readings to be
measured and reported before any adjustments to calibration are made. As
left readings are also recorded. Acceptance tolerances and maintainance
tolerances are specified in Handbook 44 and vary by Class specifications.
Most legal-for-trade requirements defer to Handbook 44.

 

[Rich Grise]

On Sat, 28 May 2005 12:33:36 -0700, Luhan Monat wrote:

Rich Grise wrote:
On Sat, 28 May 2005 08:38:23 -0600, JS2 wrote:
"Robert Baer" <robertbaer@earthlink.net> wrote in message
john.ruckstuhl@gmail.com wrote:

Bathroom scales have historically been rather (to be polite) inaccurate.
Notice in a grocery that the scales are all spring scales (ie:
inexpensive) and are marked "NOT FOR TRADE" or "NOT LEGAL FOR TRADE".
They all read *approximate* values, and if not calibrated, can be off by
20 percent of full scale (either way) for starters.
If you want more reliable or accurate readings, use a balance type of
scale: Toledo comes to mind, Cenco comes to mind; there are others.

I've noticed with balance scales that the weight shifts by several pounds
depending upon where you stand on it ... I assume you're supposed
to stand more or less in the center, an inch one way or another can
make a difference of a pound or two (important if you're doing a
sport with weight divisions).

Not only have I never heard of such a thing, I've seen the workings
of scales that go to great lengths to avoid just that. If your scale
shows different weights when the object is on different places on
the platform, then you have been robbed.

This would not explain my experience, just picking up a little extra
weight each time and getting back on the scale. It just would not move
until about 5 pounds total had been added. Only explanation I have is
that is it 'faking' the accuracy; and doing it quite intentionally.

That's why is on my list of projects for re-engineering. Maybe Mavin's
voice "You standing on my like that is just so Depressing!"

I've answered this in a different branch - the sensor has a certain
amount of hysteresis, but also excellent "repeatability" as long as
you haven't moved the sensor's threshold in between, which is what
John says is happening. The sensor takes a "set", or something very
much like that. But I guess I'd have trouble blaming sticktion when
they're using strain gauges - but anything, to measure how hard it
is being stressed or strained, has to have some kind of change take
place, or there wouldn't be any signal. Generally, that's movement
of some kind. So, if it's something that flexes, it simply doesn't unflex
back to _precisely_ the same position, for any number of reasons. At least
not right away. Probably after awhile, yes. So when he first gets on, the
sensor has been relaxing all night, so has no "set." He steps on the scale
first time, and puts whatever "set" that 166.2 puts on it. Then, when
he steps off and on, The force on it is the same, so it doesn't add any
"set", and since the thing has good repeatabilty, it reads the same. Then,
he steps on it with weights on, and it reads, say, 191.2. (It would be
very interesting to see this number, if the weights are calibrated). This
increases the "set" to S(191.2). Now, he puts 166.2 on it, but it doesn't
have enough force to even _reach_ the higher "set," so effectively zero
has backed away by 0.6, and it reads 166.8.

Nothin' to it! ;-)

Cheers!
Rich

 

[Luhan Monat]

Rich Grise wrote:

On Sat, 28 May 2005 12:33:36 -0700, Luhan Monat wrote:

Rich Grise wrote:

On Sat, 28 May 2005 08:38:23 -0600, JS2 wrote:

"Robert Baer" <robertbaer@earthlink.net> wrote in message

john.ruckstuhl@gmail.com wrote:

Bathroom scales have historically been rather (to be polite) inaccurate.
Notice in a grocery that the scales are all spring scales (ie:
inexpensive) and are marked "NOT FOR TRADE" or "NOT LEGAL FOR TRADE".
They all read *approximate* values, and if not calibrated, can be off by
20 percent of full scale (either way) for starters.
If you want more reliable or accurate readings, use a balance type of
scale: Toledo comes to mind, Cenco comes to mind; there are others.

I've noticed with balance scales that the weight shifts by several pounds
depending upon where you stand on it ... I assume you're supposed
to stand more or less in the center, an inch one way or another can
make a difference of a pound or two (important if you're doing a
sport with weight divisions).

Not only have I never heard of such a thing, I've seen the workings
of scales that go to great lengths to avoid just that. If your scale
shows different weights when the object is on different places on
the platform, then you have been robbed.


This would not explain my experience, just picking up a little extra
weight each time and getting back on the scale. It just would not move
until about 5 pounds total had been added. Only explanation I have is
that is it 'faking' the accuracy; and doing it quite intentionally.

That's why is on my list of projects for re-engineering. Maybe Mavin's
voice "You standing on my like that is just so Depressing!"


I've answered this in a different branch - the sensor has a certain
amount of hysteresis, but also excellent "repeatability" as long as
you haven't moved the sensor's threshold in between, which is what
John says is happening. The sensor takes a "set", or something very
much like that. But I guess I'd have trouble blaming sticktion when
they're using strain gauges - but anything, to measure how hard it
is being stressed or strained, has to have some kind of change take
place, or there wouldn't be any signal. Generally, that's movement
of some kind. So, if it's something that flexes, it simply doesn't unflex
back to _precisely_ the same position, for any number of reasons. At least
not right away. Probably after awhile, yes. So when he first gets on, the
sensor has been relaxing all night, so has no "set." He steps on the scale
first time, and puts whatever "set" that 166.2 puts on it. Then, when
he steps off and on, The force on it is the same, so it doesn't add any
"set", and since the thing has good repeatabilty, it reads the same. Then,
he steps on it with weights on, and it reads, say, 191.2. (It would be
very interesting to see this number, if the weights are calibrated). This
increases the "set" to S(191.2). Now, he puts 166.2 on it, but it doesn't
have enough force to even _reach_ the higher "set," so effectively zero
has backed away by 0.6, and it reads 166.8.

Nothin' to it! ;-)

Cheers!
Rich

Sorry, something is getting missed here. I kept picking up an extra
pound of stuff each time and then getting back on the scale. So it had
some chance to re-zero. But all it did was report exactly the same
weight each time. When the accumulated extra weight was about 5 pounds,
then, and only then, did it jump to a new weight. Then again, it
claimed that to be the real weight as a dropped off a pound at a time
getting on and off the scale.

The software in the scale was obviously fudging the numbers to produce a
false sense of accuracy.

--
Luhan Monat: luhanis(at)yahoo(dot)com
http://members.cox.net/berniekm
"Any sufficiently advanced magick is
indistinguishable from technology."