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Thermocouples

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nuckolls.bob(at)aeroelect
Guest

Posted: Tue Nov 16, 2010 7:43 pm Post subject: Thermocouples

At 02:40 PM 11/16/2010, you wrote:

 	  Quote: 	
		  



Hi Bob,



My recollection of the voltage curves for J and K types would

render the fabric range down at the low  voltage end for a K type.

If these are the cheap meters, you'll get better resolution with a J

because of higher voltage per degree and larger voltage at 300F.



OK, so less desirable if not useless.


	


   Okay . . . Yes, the voltage vs. temperature gradient

   for J is larger than K and therefore easier to measure

   with greater resolution.  But modern digitizing and

   processing makes this less of an issue. The display

   resolution on the Fluke 51/52 t/c meter is 0.1 C or F

   but the stated accuracy of instrument is +/- 1.1C

   with K-wire then there's accuracy of the wire itself

   which can stack another 1.5 to 2.5 degrees C error

   with either J or K assuming the wire meets industry

   performance minimums.



http://digital.ni.com/public.nsf/allkb/776AB03E065228408625727B00034E20



   Multi-meters with t/c inputs tend not to be as

   capable as a dedicated t/c device like the Fluke

   51/52 devices. I think the last time I compared one

   of my multi-meters with the Fluke, there was a

   difference of 4 degrees at 100C.



   The thrust of this missive goes to the notion

   that thermocouples and their display devices are

   subject to well understood errors. Further, one

   needs to be mindful of additional errors that can

   crop up in poorly crafted joints.



   So don't be too surprised if side-by-side t/c

   instruments reading the same point differ by

   5-10 degrees at CHT temperatures.

   Bob . . .

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rampil

Joined: 04 May 2007
Posts: 870

Posted: Wed Nov 17, 2010 7:11 am Post subject: Re: Thermocouples

Hi Bob,



Thanks for the input!



When I responded, I was not considering Fluke, HP, or Tektronix,

but rather cheapy $10 DMMs with cheap ADCs with poor temporal and voltage resolution and precision.



My concerns would be negligible on a $500 Fluke!

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_________________
Ira N224XS

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Nov 17, 2010 8:49 am Post subject: Thermocouples

At 09:11 AM 11/17/2010, you wrote:

 	  Quote: 	
		  



Hi Bob,



Thanks for the input!



When I responded, I was not considering Fluke, HP, or Tektronix,

but rather cheapy $10 DMMs with cheap ADCs with poor temporal and 

voltage resolution and precision.



My concerns would be negligible on a $500 Fluke!


	


    Understand.



    For folks interested in elevating their temperature

    measurement capabilities, an Ebay seller has about

    a half dozen Fluke 51 meters for $66.00 BuyItNow (includes

    shipping), item 170556237065.



    See also items 140478886447, 220696564187, 270664205816

   Bob . . .

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