Thermocouple time response

Discussion in 'The Projects Forum' started by firedamage, Feb 25, 2014.

  1. firedamage

    Thread Starter New Member

    Jun 17, 2013
    10
    0
    Hi all, I am doing my project to improve the time constant of type- T thermocouple. The type-T thermocouple has exposed bead and is spot welded together ,conductors are 1/0.315 mm

    Is there any way to improve type-T exposed bead thermocouple time response by modifying the thermocouple bead?

    I have try to apply the lead using soldering iron to the thermocouple bead but the time response seems to be higher than the original bead( spot welded).

    I have attach the type-T thermocouple technical sheets picture.

    Any help would be greatly appreciated.

    Thank you.
     
  2. ericgibbs

    Senior Member

    Jan 29, 2010
    2,499
    380
    hi,
    This link is for a Thermocouple App.
    http://www.picotech.com/applications/thermocouple.html

    Are you saying that you have cut off the original 'fused' thermocouple junction and tried to use solder to make a junction.?

    I have seen methods on the web, claiming discharging a 'big' capacitor thru the junction, causes the wires to fuse together.?

    E
     
  3. firedamage

    Thread Starter New Member

    Jun 17, 2013
    10
    0
    hi ericgibbs, thank you for the reply.

    Yes, i have to cut off the original 'fused' thermocouple junction and tried to use solder to make a junction. but the soldered bead time response is lower compared to the original 'fused' thermocouple junction.

    The problem i can think of using solder for the bead is that you cant make the volume of the bead as small as the original 'fused' junction, so the time response of thermocouple that used solder will be higher due to larger volume.

    Is there any other way create thermocouple junction?
    l
    thank you very much :)
     
  4. ericgibbs

    Senior Member

    Jan 29, 2010
    2,499
    380
    firedamage likes this.
  5. Sensacell

    Well-Known Member

    Jun 19, 2012
    1,127
    266
    You need to minimize the thermal mass, smaller wire diameter and smallest junction between the two thermocouple wires.
     
    firedamage likes this.
  6. firedamage

    Thread Starter New Member

    Jun 17, 2013
    10
    0
    hi sensacell,

    the only options I have is to minimize the thermal mass and junction. As I noticed, the original junction(spot welded) is already very small, is there any way possible to make the junction/mass even smaller so that time response can be improved?

    thanks
     
  7. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,769
    969
    http://www.omega.com/temperature/Z/ThermocoupleResponseTime.html
    butt welded..
    in general..smaller the diameter the faster it will respond. junction grounding can decrease response time too..

    Why is this even your project?.. project for what?.. what response time do you need?
    Its all been done before and if omega hasn't done it there is no need to..
     
  8. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    what are you attempting to measure the temprature of?
     
  9. firedamage

    Thread Starter New Member

    Jun 17, 2013
    10
    0
    the thermocouple I am investigating is exposed bead thermocouple, thus its junction cannot be grounded..?

    this is my master in mech engineering final year project.

    The project aim is to investigate the relationship between different thermal masses with time response and improve its time constant.


    The response time that I need should be smaller than the original junction ('fused') type-T exposed bead thermocouple which the technical sheet i have attach in the first post of this thread.
    Any idea to make the bead smaller than the original(' spot welded') ? i have try soldering but does not work.
     
    Last edited: Feb 26, 2014
  10. firedamage

    Thread Starter New Member

    Jun 17, 2013
    10
    0
    i am trying to measure air flow temperature and water temperature.
     
  11. ericgibbs

    Senior Member

    Jan 29, 2010
    2,499
    380
    hi fd,
    If I understand your application correctly.?
    Why are you using a thermocouple for such a limited range of temperatures.?

    Can you post the temperature range required.

    E
    EDIT:
    Have you considered this method.?
    Ref attachment
     
    Last edited: Feb 26, 2014
    firedamage likes this.
  12. firedamage

    Thread Starter New Member

    Jun 17, 2013
    10
    0
    The temperature required around 0 degree Celsius to 150 degree Celsius. I would like to use the thermistor you attached but I am bound to the project scope... that is to investigate the effect of thermal mass on time response of thermocouple and improve its time constant. I have already measured the time constant for the original (' spot welded') exposed bead thermocouple, now I am trying to minimize the thermal mass so that it's response time can be improved but I can't find any way to make it even smaller than the spot welded one...

    Is there any other ways or methods to reduce the time response?

    Thank you. You guys are helping me a lot

    Sry for the bad English.
     
  13. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,769
    969
    butt weld > bead weld
    butt weld = less mass than bead weld

    Its YOUR final project... YOU are supposed to determine if there is a better way.. not by asking others.


    Soldering is NOT how you join thermocouple wires.. Welding IS.
     
    firedamage likes this.
  14. firedamage

    Thread Starter New Member

    Jun 17, 2013
    10
    0
    Thank you :)
     
  15. burger2227

    Member

    Feb 3, 2014
    190
    24
    How about grinding it a bit? :D
     
    firedamage likes this.
  16. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    how aout increasing the flow of the media measured? that should decrease time to stabilize the thermocouple.
     
    firedamage likes this.
  17. firedamage

    Thread Starter New Member

    Jun 17, 2013
    10
    0
    wow.never think of this. lol nice idea:D
     
Loading...