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'[EE]: Challenge: measuring temperature and pressur'
2002\06\06@030941 by Vasile Surducan

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"Hi world !" -- sounds familiar for LCD beginer users isn't it ?

I'm glad on these lists are people which are very familiar with
temperature measurements and thermostats. I am proposing to you a
challenge: measuring temperature and pressure in a microwave digestion
reaction chamber.

First a very few words about microwave and digestion: microwave radiation
distribution inside a chamber is defined by the Pointing vector, absorbion
of microvawe radiation depends by the permitivity dielectric tensor of the
probe, with other words imersing a termocouple, RTD or a DS1820 inside a
microwave chamber will blow you the sensor almost in any circumstances (
there are a few condition in which not...) Digestion, means the probe is
imersed first in some ( strong ) acids, then the sample cells ( one, four,
six etc ) are placed inside the microvawe cavity. Then a microcontroler is
supervising the treatment process ( microwave power radiation and
microwave pulses parameters )
The temperature may be up to 300...500C C and the pressure up to 30
atmosferes. Imagine also how strong are the acid vapours inside and what's
happened when the sample cells are opened after such a treatment.
Now is your turn, my friends: what do you suggest ? non contact
temperature ? but the pressure ?


thank you,
Vasile
http://www.geocities.com/vsurducan

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2002\06\06@060847 by Jinx

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> but the pressure ?

Gold piston ? Too hot ? Titanium piston ? Could you
arrange a motor to push against something (eg perhaps
a piston or bellows ????) from outside the vessel and
measure the force required ?

========================

I'll hop inside with a barometer for $2-a-day wages
(+ health benefits)

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2002\06\06@074506 by Russell McMahon

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> > but the pressure ?
>
> Gold piston ? Too hot ? Titanium piston ? Could you
> arrange a motor to push against something (eg perhaps
> a piston or bellows ????) from outside the vessel and
> measure the force required ?
>
> ========================
>
> I'll hop inside with a barometer for $2-a-day wages
> (+ health benefits)


If you'll take $1 a day it's sure to be a done deal (but you'll need to
carry your own health insurance).


           RM

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2002\06\06@075855 by Russell McMahon

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>I am proposing to you a challenge: measuring temperature and pressure in a
microwave digestion
> reaction chamber.

> First a very few words about microwave and digestion: microwave radiation
> distribution inside a chamber is defined by the Pointing vector, absorbion
> of microvawe radiation depends by the permitivity dielectric tensor of the
> probe, with other words imersing a termocouple, RTD or a DS1820 inside a
> microwave chamber will blow you the sensor almost in any circumstances (
> there are a few condition in which not...)

A continuous metal shield will protect any circuitry inside from microwave
radiation (or any other em radiation). Think of it as a Faraday cage. I have
a domestic microwave oven that has a metal meat probe connected by a
flexible
wire cable to a 1/4 inch socket in the top of the microwave. The turntable
rotates +/1 180 degrees to stop the cable tangling. I have no idea what
technology is used for the sensor inside the probe but suspect thermistor.
This probe has worked with occasional use for 15 odd years. I imagine that
the cable is coaxial so that the microwave radiation does not "see" a slot
to produce circulating currents around the perimeter of. This arrangement
should be directly applicable to your application with almost any sensor of
your choice sealed inside the metal sleeve with a coax cable feed.

Here's a range of temperature sensors for microwave oven use -

       http://www.shibaura-e.co.jp/english/product/sensor/cook2.htm

And there are many many more. None SEEM to obviously use coaxial
connections.

       http://www.jamestech.co.kr/english/product/product6.htm

If you twist the wires with a pitch substantially finer than the wavelength
involved (12 cm) you theoretically have not net induced voltage. YMMV :-)

Here's some fibre optic temperature sensors. Don't know how the pressure
would affect them.

       http://www.fiso.com/temp.htm




       Russell McMahon
>

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2002\06\06@083226 by Jinx

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> > > but the pressure ?

What do space probes use ? You don't get much tougher
than Venus. I know the tx didn't last long, but perhaps the
sensors help out for a while

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2002\06\06@084027 by Vasile Surducan

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On Thu, 6 Jun 2002, Russell McMahon wrote:

{Quote hidden}

 Good observation Russell. But unfortunately there are big differences
in microwave energy density between a standard microwave oven and a
reaction chamber. Imagine the same energy field ( generated by a 1200W
magnetron ) in a coaxial cavity of 5cm tall and 3 cm diameter.
( fortunately the power can be fine adjusted... )
Such sensors as you mentioned here can't be used only mounted in
the minimum
microwave electric field points. Unfortunately measuring temperature there
have nonsense for my application. The smallest reaction cells have only
5...10ml of
probe, I can measure the temperature outside the cells in the microvawe
cavity but that will provide me unrelevant measurements ( and there is a
whole theory why...) .
Many producers of digestion systems are doing in such way. For these, the
romanian proverb: "outside the fence is well painted, inside the leopard is
waiting" is very appropiate.
BTW, any fine twisted wire inside such a microwave field, are blowed on
the
wals at as low power as 100W of microwave radiation... this is not
happening into domestic owen because the field distribution is very poor,
thats why almost all of these owens have a homogenity device
( moving dish or propeller )
Thanks for the links, I will take a look.

Vasile

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2002\06\06@085158 by Chris Loiacono

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I am proposing to you a
> challenge: measuring temperature and pressure in a microwave digestion
> reaction chamber.
>

So, exactly what range is the pressure in?

Why not non-contact temp measurement? - Try Exergen.com

Chris

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2002\06\06@105118 by Doug Butler

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What is the wall of the chamber made out of?  There are plenty of "flush
diaphragm" commercial pressure transducers with diaphragms of stainless
steel or titanium.  We use them for oceanographic work.  If you use soft
copper for the mounting gasket they should be very EMI proof.  Also look at
transducers for "sanitary" use.

Doug Butler
Sherpa Engineering


> {Original Message removed}

2002\06\06@125222 by Scott Stephens

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From: Vasile Surducan <spam_OUTvasileTakeThisOuTspamS3.ITIM-CJ.RO>
Subject: [EE]: Challenge: measuring temperature and pressure in very harsh
environement


>Now is your turn, my friends: what do you suggest ? non contact
>temperature ? but the pressure ?


Measure the change in refractive index with a laser beam? Perhaps the
microwave mode pattern could be sampled with phase sensitive probes, to see
how the plasmoid scatters radiation, which would probably depend on density,
pressure and temperature.

Scott

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2002\06\06@125522 by Scott Stephens

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From: Jinx <.....joecolquittKILLspamspam@spam@CLEAR.NET.NZ>
Subject: Re: [EE]: Challenge: measuring temperature and pressure inveryharsh
environement


>> > > but the pressure ?
>
>What do space probes use ? You don't get much tougher
>than Venus. I know the tx didn't last long, but perhaps the
>sensors help out for a while


Diamond windows IIRC. Only lasted an hour in the high-pressure sulfuric
acid.

Scott

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2002\06\06@130423 by Mark Perri

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Assuming you can use metal in your microwave chamber,
I think you'd be better off using Monel or Inconel for the diaphragm
depending on what acids you're using, unless they're in low enough
vapor pressures.  For the gasket, you might want to look at Viton
or even Kalrez (assuming they'll hold 30 atm).  Or you'd have to weld
everything together.

Here is a link to a microwave synthesis setup that uses some
nonmetal parts -- maybe you can contact them and see what they
use.  Probably a mix of teflon, viton, and ceramics.

http://www.cem.com/products/MARSsyn.html


>What is the wall of the chamber made out of?  There are plenty of "flush
>diaphragm" commercial pressure transducers with diaphragms of stainless
>steel or titanium.  We use them for oceanographic work.  If you use soft
>copper for the mounting gasket they should be very EMI proof.  Also look at
t>ransducers for "sanitary" use.

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2002\06\06@134113 by Peter L. Peres

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You can measure both temperature and pressure using mechanical
contraptions, and from a distance f.ex. using a laser beam. I'd make the
contraption(s) from the same material as the crucibles that hold the
substances to be processed, or better, machine them into the crucibles.

A gas (vacuum) bubble with a thin skin near the outer surface of a
crucible with an interference type mirror deposed on the outside makes a
temperature (pressure)  sensor when used together, good for remote reading
using a laser and a camera and computer with image processing for readout.
Bonus: you can read 20 crucibles on the same image together if you want
to. You may have to use some fancy camera optics and windows though. Is
there smoke or worse in the chamber while working ?

Peter

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2002\06\06@135723 by David Minkler

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Hi Vasile,

We ( http://www.luxtron.com ) manufacture temperature measuring
instruments for use in harsh environments (semiconductor processes,
microwave systems, distribution transformers).  We use two different
technologies, suitable for different temperature ranges.  No electrical
connection to measured point.  I'm not sure how you would measure
pressure but it sounds like Doug is on the right track there.

Regards,
Dave

Vasile Surducan wrote:
{Quote hidden}

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2002\06\06@172729 by Jinx

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A mercury barometer would work wouldn't it ? You don't
want the whole thing inside the chamber - too hot for the
mercury of course

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2002\06\07@022805 by Vasile Surducan

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On Thu, 6 Jun 2002, Chris Loiacono wrote:

> I am proposing to you a
> > challenge: measuring temperature and pressure in a microwave digestion
> > reaction chamber.
> >
>
> So, exactly what range is the pressure in?

 1 to max 30 atmosfere, but above 10 atmosfere we could
stop the process with an emergency out
>
> Why not non-contact temp measurement? - Try Exergen.com
>

 Hmm, I have doubts will be a correct measurement because: it needs a
cuartz optical fibre from the probe to the temperature sensor. The system
can measure correct just the surface temperature of the mixture
acid-sample. When the fibre is imersed the mixture may be less or more
infrared opaque. Remember I need to digest tousens of sample types from
soil to human kidneys...
There is also a problem with temperature distribution which has a
variation of 100C in 5 seconds of treatment.

Vasile

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2002\06\07@024251 by Vasile Surducan

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Joe, the real problem is not the pressure sensor itself ( maybe there is a
little problem here too ) but the way in which the sensors ( temperature
and pressure ) is modifying the microwave distribution field in small
spaces ( max 10ml of sample ). You realise what's happend if a small 2mm
diameter pipe ( pressure sensor connection ) and another 1mm tick wire (
temperature sensor ) are both imersed in the cell. The microwave
distribution will be "upside-down" like the normal computed conditions.
The whole microwave field will be concentrated on these "parasites"
instead of the sample. We know that, because we had developed an imersion
microwave termographic transducer ( it get a bronz medal at the
international patents competition at Geneva, last year...)
which show us exactly what's happened inside the cell.
I have used your piston ideea Joe, but ih hasn't enough resolution at
small pressure ( near 1 atm )

regards, Vasile


On Thu, 6 Jun 2002, Scott Stephens wrote:

{Quote hidden}

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2002\06\07@024307 by Vasile Surducan

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Could you tell me which is the smalest diameter of such diaphragms ?
Thanks

On Thu, 6 Jun 2002, Doug Butler wrote:

> What is the wall of the chamber made out of?  There are plenty of "flush
> diaphragm" commercial pressure transducers with diaphragms of stainless
> steel or titanium.  We use them for oceanographic work.  If you use soft
> copper for the mounting gasket they should be very EMI proof.  Also look at
> transducers for "sanitary" use.
>
> Doug Butler
> Sherpa Engineering
>
>
> > {Original Message removed}

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