Just a thought - if you are using an Arduino for control, wouldn't it be easier to use glass bead thermistors rather than thermocouples. This type are used by the Reprap project http://datasheet.octopart.com/01T1002FP-Vishay-datasheet-1103.pdf and seem to be accurate to about 1% without having to worry about cold junction temperatures or small signal voltages...
Ian ________________ Ian W. Wright Sheffield UK On 13/02/2011 17:41, John Thornton wrote: > I'm measuring the cabinet temperature of a smoker with a range of 100F - > 350F and internal food temperatures from 40F to 250F or so. The > thermocouples I'm using are Auber Instruments smoker and meat > thermocouples. All the temperature devices are in the same Arduino Uno > enclosure except for the thermocouples which are in the smoker cabinet. > From some discussion on the IRC a while ago the 4052 mux with the 6075 > (just because of package) seem to be the best fit ATM for me. > > Thanks > John > > Kent A. Reed wrote: >> On 2/13/2011 8:59 AM, John Thornton wrote: >> >>> In my continuing search to get temperature information into the computer >>> at a reasonable cost I came across a neat thing called a multiplexer. >>> I'm sure all of you know about them all ready :) but I'm a little slow >>> in electronics. Anyway my thought is to use a multiplexer to get 4 >>> thermocouples into one MAX6675. This would make the MAX6675 a much more >>> attractive way to read temperatures. The big question is what >>> multiplexer to use, there are thousands of them! On my prototype shield >>> on the Arduino Uno I have one SOIC pad for the MAX6675 and one DIP area >>> that can handle up to a 20 pin DIP chip. Googling for Arduino and >>> multiplexer I came across one example that mentions using a 4051 chip. >>> Doing a search on DigiKey for 4051 turns up quite a bit to pick from and >>> after drilling down to 16 pin DIP packages a page full. Seems like most >>> of the differences are on-state resistance, voltage supply source, >>> voltage supply, current supply... >>> >>> I also came across this package from down under that is doing the same >>> thing using an ADG608 multiplexer. Searching for that on Digikey I see >>> it comes in a 16 pin DIP package. I wonder if that would be a better choice? >>> >>> http://www.oceancontrols.com.au/KTA-259.html >>> >>> Any suggestions are welcome on picking one. >>> >>> Thanks for all the help so far on this. >>> >>> John Thornton >>> >>> >> John: >> >> Don't let the cart get in front of the horse. >> >> What temperatures are you trying to measure and in what environment? Is >> the measurement local or remote? How accurate does the measurement have >> to be? >> >> Thermocouples may be the way to go and then again they may not be. Even >> if they are, there's thermocouples and then there's thermocouples, and >> others have already alluded to gotchas involved with using them >> properly. The NIST library had a whole bookshelf full of reference books >> on the subject. >> >> Please tell us a bit more so we don't end up optimizing the wrong >> solution for you. (Don't ask me how I know!) >> >> Regards, >> Kent >> >> >> >> ------------------------------------------------------------------------------ >> The ultimate all-in-one performance toolkit: Intel(R) Parallel Studio XE: >> Pinpoint memory and threading errors before they happen. >> Find and fix more than 250 security defects in the development cycle. >> Locate bottlenecks in serial and parallel code that limit performance. >> http://p.sf.net/sfu/intel-dev2devfeb >> _______________________________________________ >> Emc-users mailing list >> Emc-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/emc-users >> > ------------------------------------------------------------------------------ > The ultimate all-in-one performance toolkit: Intel(R) Parallel Studio XE: > Pinpoint memory and threading errors before they happen. > Find and fix more than 250 security defects in the development cycle. > Locate bottlenecks in serial and parallel code that limit performance. > http://p.sf.net/sfu/intel-dev2devfeb > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > > > ----- > No virus found in this message. > Checked by AVG - www.avg.com > Version: 10.0.1204 / Virus Database: 1435/3440 - Release Date: 02/12/11 > > ------------------------------------------------------------------------------ The ultimate all-in-one performance toolkit: Intel(R) Parallel Studio XE: Pinpoint memory and threading errors before they happen. Find and fix more than 250 security defects in the development cycle. Locate bottlenecks in serial and parallel code that limit performance. http://p.sf.net/sfu/intel-dev2devfeb _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
