Post by thread:[EE]: Challenge: measuring temperature and pressur

"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 -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

> > 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 -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

>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 > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

On Thu, 6 Jun 2002, Russell McMahon wrote: {Quote hidden}> >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. > 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 -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

From: Vasile Surducan <spam_OUTvasileTakeThisOuTS3.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 -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

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. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

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 -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

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}> > "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 > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

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 -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

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}> From: Jinx <joecolquittKILLspamCLEAR.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 > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics