Satisfy my curiosity

[Charlie Bress]

I had one of those little kitchen scales that provide a digital readout and
also let you zero the reading to remove the weight of a bowl etc.

Well the thing got dunked in the water and went belly up.
Not a great loss, it was about 8 or 10 years old.
The scale had the usual caveat of "no user parts- do not open".
Now I could open it with no fear of breaking anything.

I am curious about the sensing technology.
I have worked in the strain gauge industry and I have used piezoelectric
transducers for vibration studies, but I cannot tell what the technology
involved here is.
It might just be a piezo element that is not encased.

Can someone identify what is used in these scales? Then I can go read up on
it.

Curiosity killed the cat, but satisfaction brought it back.

Thanks, Charlie

 

[Sam Goldwasser]

I had one of those little kitchen scales that provide a digital readout and
also let you zero the reading to remove the weight of a bowl etc.

Well the thing got dunked in the water and went belly up.
Not a great loss, it was about 8 or 10 years old.
The scale had the usual caveat of "no user parts- do not open".
Now I could open it with no fear of breaking anything.

I am curious about the sensing technology.
I have worked in the strain gauge industry and I have used piezoelectric
transducers for vibration studies, but I cannot tell what the technology
involved here is.
It might just be a piezo element that is not encased.

Can someone identify what is used in these scales? Then I can go read up on
it.

Curiosity killed the cat, but satisfaction brought it back.

Can you locate the sensors? Not just resistive strain gauges?

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[Tom McEwan]

I had one of those little kitchen scales that provide a digital readout and
also let you zero the reading to remove the weight of a bowl etc.

Well the thing got dunked in the water and went belly up.
Not a great loss, it was about 8 or 10 years old.
The scale had the usual caveat of "no user parts- do not open".
Now I could open it with no fear of breaking anything.

I am curious about the sensing technology.
I have worked in the strain gauge industry and I have used piezoelectric
transducers for vibration studies, but I cannot tell what the technology
involved here is.
It might just be a piezo element that is not encased.

Can someone identify what is used in these scales? Then I can go read up on
it.

I've ripped open a busted up set of digital scales in the hope of finding
something useful, but was very disappointed.

All they contained were a set of metal plates with air gaps between them,
alternately connected to the base of the unit and the weighing surface - the
tiny shifts in the position of the weighing platform moved the plates
laterally, making them act like a big variable capacitor.

Got seriously hacked off about that - I was hoping for some useful pressure
transducers or something, not hunks of pressed sheet metal...

Tom

 

[N Cook]

up

I've ripped open a busted up set of digital scales in the hope of finding
something useful, but was very disappointed.

All they contained were a set of metal plates with air gaps between them,
alternately connected to the base of the unit and the weighing surface - the
tiny shifts in the position of the weighing platform moved the plates
laterally, making them act like a big variable capacitor.

Got seriously hacked off about that - I was hoping for some useful pressure
transducers or something, not hunks of pressed sheet metal...

Tom

Yes cheepo kitchen scales measure capacitance.
I took one apart for same curiosity
More precise and linear scales eg postal weighing
scales use proper balanced strain guage and
load cell design.


Repair briefs and Repair Tips etc on
http://homepages.tcp.co.uk/~diverse/

 

[Charlie Bress]

Yes cheepo kitchen scales measure capacitance.
I took one apart for same curiosity
More precise and linear scales eg postal weighing
scales use proper balanced strain guage and
load cell design.

This one was pretty accurate. It measured to 0.1 ounces and always agreed
with the post office scale on those occasions that I used it to see what a
small package weighed.

What is the load cell technology? Is it piezo or something else?
Charlie

 

[t.hoehler]

This one was pretty accurate. It measured to 0.1 ounces and always agreed

with the post office scale on those occasions that I used it to see what a
small package weighed.

What is the load cell technology? Is it piezo or something else?
Charlie

Hi Charlie, I too, had a scale go bad, the lcd display crapped out, so I
opened it up, they are so cheap not worth fooling with. This one was a
letter weighing scale that was part of a Pitney Bowes system, had a data
output jack that fed the postage meter. Anyway, it used resistive strain
gauges in a bridge, very, very accurate. The mechanism inside looked pretty
cheesy, but it worked well for about ten years of everyday use.

regards,
Tom

 

[The Real Andy]

I had one of those little kitchen scales that provide a digital readout and
also let you zero the reading to remove the weight of a bowl etc.

Well the thing got dunked in the water and went belly up.
Not a great loss, it was about 8 or 10 years old.
The scale had the usual caveat of "no user parts- do not open".
Now I could open it with no fear of breaking anything.

I am curious about the sensing technology.
I have worked in the strain gauge industry and I have used piezoelectric
transducers for vibration studies, but I cannot tell what the technology
involved here is.
It might just be a piezo element that is not encased.

Can someone identify what is used in these scales? Then I can go read up on
it.

Curiosity killed the cat, but satisfaction brought it back.

Thanks, Charlie

Chances are its either going to be a half bridge load cell, or
capacitive sensor. If your lucky, it may even be a full bridge load
cell. Piezo elements are rarely used for standard weighing
applications, as you suggest they are mainly reserved for vibration
analysis. Some smaller lab scales will use a voicecoil and fletches
for a load cell, but these are usually quite expensive.

 

[Franc Zabkar]

I had one of those little kitchen scales that provide a digital readout and
also let you zero the reading to remove the weight of a bowl etc.

Well the thing got dunked in the water and went belly up.
Not a great loss, it was about 8 or 10 years old.
The scale had the usual caveat of "no user parts- do not open".
Now I could open it with no fear of breaking anything.

I am curious about the sensing technology.

I have these scales (model MS-7):
http://www.msiusa.com/consumers/bath_scales_detail.asp?ID=69

They are described as "Lithium Electronic Strain Gauge Scales". Does
anybody know how these work?


- Franc Zabkar

 

[Franc Zabkar]

I have these scales (model MS-7):
http://www.msiusa.com/consumers/bath_scales_detail.asp?ID=69

They are described as "Lithium Electronic Strain Gauge Scales". Does
anybody know how these work?

I just discovered that there is no user replaceable battery, so I
guess there is a "lifetime" lithium cell inside.


- Franc Zabkar

 

[Charlie Bress]

I just discovered that there is no user replaceable battery, so I
guess there is a "lifetime" lithium cell inside.

The one I had was an MS11 made by the same company. It did have a commercial
2032 lithium cell inside.
The cell was located in a compartment that was part of the digital display.
Having done the autopsy, I can see how a knowledgeable person could
replace the cell if the original died. In my case, the cell was still good.
I could zero the scale, but it no longer read light weights.

I worked with strain gauges in 1957. At that time, they had dimensions in
the order of inches or large fractions of an inch. It is apparent now that
different materials have enabled great reduction in size.

See the tutorial at
http://zone.ni.com/devzone/conceptd.nsf/webmain/C83E9B93DE714DB08625686600704DB1?OpenDocument

or simply do a Google search on strain gauge.

Charlie