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'[EE] Any suggestions for measuring weight?'
2006\11\09@212710 by Andy Tuthill

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I'm working on a project where I will need to measure the weight of wooden
blocks up to 4 kg's max.  The hard part is they will be in a drying kiln so
the conditions will be up to 100C and 100% relative humidity, or steam.  I
have looked into some load cells but they can be somewhat expensive.  Before
spending the cash to get one I wanted to see if anyone had any suggestions.

Regards,
Andy

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2006\11\09@231318 by cdb

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face
I wonder if my favourite gizmo, peizo film or similar would work here?

Colin

:: The hard part is they will be in a drying kiln so
::
:: the conditions will be up to 100C and 100% relative humidity, or
:: steam.  I
:: have looked into some load cells but they can be somewhat
:: expensive.
.

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2006\11\10@012357 by Denny Esterline

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> I'm working on a project where I will need to measure the weight of wooden
> blocks up to 4 kg's max.  The hard part is they will be in a drying kiln so
> the conditions will be up to 100C and 100% relative humidity, or steam.  I
> have looked into some load cells but they can be somewhat expensive.  Before
> spending the cash to get one I wanted to see if anyone had any suggestions.
>
> Regards,
> Andy

What level of precision will you need?

100 C and 100% humidity isn't realy that bad, you just have to think lateraly.

My first instinct would be some sort of linkage to a more traditional scale outside the hostile enviroment, that might even include some type of hydraulic system (common automotive coolant, properly mixed, is good well beyond 100C)

A mechanical spring ballance should be fine too, though it might need recalibrated at that temperature depending on your needed level of precision and the material used for the spring.

Strain gauges are little more than a metal foil resistor, there's no reason why they couldn't be used in such an enviroment. You'll likely run into issues with bonding them, but that's solveable. And thermal compensation becomes much more important, but there are ways of dealing with that too.

-Denny


2006\11\10@033312 by slippyr4

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I second strain gauges. There are many grades of cyanoacrylate that
could cope with those conditions - although the humidity might prevent
the glue from lasting forever.

I've seen strain gauges used frequently for strain measurement on
steam turbine housings, where ambient temperature can be in the
600-700 celcius range.

On 10/11/06, Denny Esterline <.....firmwareKILLspamspam@spam@tds.net> wrote:
{Quote hidden}

> -

2006\11\10@040359 by Gerhard Fiedler

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Denny Esterline wrote:

> Strain gauges are little more than a metal foil resistor, there's no
> reason why they couldn't be used in such an enviroment. You'll likely
> run into issues with bonding them, but that's solveable. And thermal
> compensation becomes much more important, but there are ways of dealing
> with that too.

You can place two (or four) of them on opposite sides of the strained part
and put them in a bridge. Doubles (quadruples) the strain signal and
eliminates the temperature signal.

Gerhard

2006\11\10@150236 by Walter Banks

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Make your own load cell with strain gages.
They are low cost, linear over a working range easy to calibrate
and quite easy to work with. What precision do you need?.

Andy Tuthill wrote:

{Quote hidden}

> -

2006\11\10@182854 by Shawn Wilton

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Everyone keeps mentioning strain gauges.  Good supplier would be...?

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Shawn Wilton (b9 Systems)
http://b9Systems.com  <- New web page

2006\11\11@091146 by Vasile Surducan

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On 11/10/06, Andy Tuthill <azandy63spamKILLspamhotmail.com> wrote:
> I'm working on a project where I will need to measure the weight of wooden
> blocks up to 4 kg's max.  The hard part is they will be in a drying kiln so
> the conditions will be up to 100C and 100% relative humidity, or steam.

You are trying to measure the wood moisture using a gravimetric
methode (by measuring the weight during the drying process, right?

Vasile

2006\11\11@095434 by Tony Smith

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> On 11/10/06, Andy Tuthill <.....azandy63KILLspamspam.....hotmail.com> wrote:
> > I'm working on a project where I will need to measure the weight of
> > wooden blocks up to 4 kg's max.  The hard part is they will be in a
> > drying kiln so the conditions will be up to 100C and 100%
> relative humidity, or steam.
>
> You are trying to measure the wood moisture using a
> gravimetric methode (by measuring the weight during the
> drying process, right?
>
> Vasile


That's the easiest way.

After you cut up the tree, you seal the ends (to stop rapid drying which
causes cracks) and weigh it.  Ever so often you weigh the piece again,
eventually the weight will stabilise, meaning it's ready to use.  A bit like
charging a battery.

Personally, I'd put the wood on a sprung platform, and measure its height.
Dry wood means constant weight means platform stops rising.

Tony

2006\11\11@102316 by Vasile Surducan

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On 11/11/06, Tony Smith <EraseMEajsmithspam_OUTspamTakeThisOuTrivernet.com.au> wrote:
{Quote hidden}

It's just 4Kg !  If it's pine, could be one board of 4m (or less)
long, 20 cm wide and 2.5cm thik. There are many alternative methodes
for moisture measurements on wood.

Vasile

2006\11\11@112930 by Tony Smith

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> > That's the easiest way.
> >
> > After you cut up the tree, you seal the ends (to stop rapid drying
> > which causes cracks) and weigh it.  Ever so often you weigh
> the piece
> > again, eventually the weight will stabilise, meaning it's ready to
> > use.  A bit like charging a battery.
> >
> > Personally, I'd put the wood on a sprung platform, and
> measure its height.
> > Dry wood means constant weight means platform stops rising.
>
> It's just 4Kg !  If it's pine, could be one board of 4m (or
> less) long, 20 cm wide and 2.5cm thik. There are many
> alternative methodes for moisture measurements on wood.
>
> Vasile


It gets more exciting if it's a plank, you need to weigh it down to stop it
warping.

You can get wood moisture meters, essentially they just measure the
resistance between two probes.  In this case, you need to open the kiln,
poke the meter in etc etc.  You can pump air thru the kiln and measure the
moisture content.  Weight is easier, especially for a one-off.

Hobbyist types do weight.  Seal, weigh, toss in corner, repeat.  Some people
dry wood in microwave ovens.

Commercial drying varies.  Some just pile it up and wait.  I've no idea how
the kilns work on an industrial scale, at a guess I'd say measuring the
moisture content of the air.  Not something you can knock up in your lunch
hour.

Why over-complicate things?  Sure, it would be nice to hook up a PIC to the
kiln and have it email you when the moisture contents hits 5%, but hanging
it off a fishing scale, looking thru the glass door and writing down the
weight every few hours is easier.  In fact the OP would be finished by
now...  Presumably there's a good reason why he hasn't done so, but until
then...

Tony

2006\11\12@144804 by Andy Tuthill

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Thanks everyone for the good suggestions.  Sorry I forgot to include the
resolution.  We would like to get 10 grams minimum but 1 gram would be
ideal.  The 30 test blocks are 600mm long sections of 2x4 inch pine.

The test chamber these will be in is roughly 1 meter across and high by 3
meters long.  One side wall opens to allow access.  Currently there is a
rack which supports the test blocks which has 4 posts through the floor to
some load cells.  This was designed to allow weighing all of the blocks
together but now the science team wants to weigh each one separately.  They
haven't decided if I will get to drill lots of holes in the chamber floor
but that would make life much easier for me.

One suggestion made was to make one scale which could move from block to
block during the drying process, similar to a printer head.  Continuous
measurements are not needed so this is one possibility.  It would also be
preferred over drilling lots of holes.

Thanks again.  I appreciate a good professional opinon.

Regards,
Andy

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2006\11\12@150203 by Andy Tuthill

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Hi Tony and Vassile,

The purpose of the project is not so much to test the moisture content of
the wood, it is to improve the performance of the kiln.  I need 'a better
mousetrap' than the one used to get more detailed data as the process is
modified.  Opening the kiln during the process destroys the conditions and
stops the test as it can't be restarted.

I'm working off the requirements that the science team has given me and also
within the limits of what they are allowing me to do to modify their test
kiln.  If you would like to see more just check out the company web site at
http://www.ensisjv.com.  This project isn't one featured but it will give you some
idea of what I'm working with as the staff electronics engineer.

I do like the idea of the fish scale though. <G>

Regards,
Andy

>From: "Tony Smith" <@spam@ajsmithKILLspamspamrivernet.com.au>
....
>Why over-complicate things?  Sure, it would be nice to hook up a PIC to the
>kiln and have it email you when the moisture contents hits 5%, but hanging
>it off a fishing scale, looking thru the glass door and writing down the
>weight every few hours is easier.  In fact the OP would be finished by
>now...  Presumably there's a good reason why he hasn't done so, but until
>then...
>
>Tony
>
>

2006\11\12@164010 by Richard Prosser

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Is there a window in the access wall? - I'm thinking of hanging the
blocks from a spring & monitoring via a video camera or laser with a
reflector moujnted on each block.

RP

On 13/11/06, Andy Tuthill <KILLspamazandy63KILLspamspamhotmail.com> wrote:
{Quote hidden}

> -

2006\11\12@225629 by Rich

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Typical method is load cell.  How much weight and how accurate do you need
to be?

----- Original Message -----
From: "Andy Tuthill" <RemoveMEazandy63TakeThisOuTspamhotmail.com>
To: <spamBeGonepiclistspamBeGonespammit.edu>
Sent: Sunday, November 12, 2006 2:47 PM
Subject: Re: [EE] Any suggestions for measuring weight?


{Quote hidden}

> --

2006\11\13@001750 by Vasile Surducan

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On 11/12/06, Andy Tuthill <TakeThisOuTazandy63EraseMEspamspam_OUThotmail.com> wrote:
> Thanks everyone for the good suggestions.  Sorry I forgot to include the
> resolution.  We would like to get 10 grams minimum but 1 gram would be
> ideal.

 Well, at 100C and 100%RH,  I think you're a little bit optimistic
about 1g resolution.
If would be 1g resolution and 40g reproducibility (precision), maybe
would be possible.
This means 1% which is hard to get on industrial processes at this
temperature ans humidity.
Even you will tell me you already got this precision I will be tempted
to not belive you, and have very good reasons why.
:)

best regards,
Vasile

2006\11\13@044639 by Alan B. Pearce

face picon face
>They haven't decided if I will get to drill lots of holes in the
>chamber floor but that would make life much easier for me.

Just what is the temperature range? To me that is the biggest hurdle to
putting suitable loadcells inside the chamber, as sealing against moisture
is relatively easy (many suitable loadcells will be sealed anyway for
outside use)

Then you may be able to use the existing holes to put connectors to the
loadcells inside the chamber.

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