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Temperature sensor

Discussion in 'Sensors and Actuators' started by KTW, Feb 8, 2017.

  1. KTW

    KTW

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    Feb 22, 2015
    I've made an emissions system smoker and the temperature control didn't come with a heat resistant probe so I purchased one but it didn't match the original probe.
    I added 10.5k resistors to match the ambient temperature of the original but it is stuck on 23.5oC.
    Does anyone know if I can get this heat resistant probe to work?
    I think they just work on resistance.
    Thanks.
    temp. sensor.JPG
     
    Last edited by a moderator: Feb 10, 2017
  2. TCSC47

    TCSC47

    34
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    Mar 7, 2016
    Could you give component numbers for the temperature sensors and the cct diag of the temperature control circuit?
     
  3. KTW

    KTW

    273
    15
    Feb 22, 2015
    I was just checking the resistance and comparing the two and I find that the original is 12.5k at ambient and when heat is applied it changes to 8.0k and the numbers continue to drop.
    The new probe is at .10k and the numbers change to .20k and continue to rise.
    The original can change with body temperature and the new probe requires excessive heat to change the resistance and the two appear to work in opposite directions so I can't see this new probe will work with my control.
    I can hunt for the specs.
    I'll likely have to use a shielding braid over the original.

    I think this new PT100 platinum sensor is for data.
    http://www.ebay.com/itm/141937267189?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT

    Control
    http://www.ebay.com/itm/Digital-LCD...stat-Sensor-/262563603517?hash=item3d2202a43d
     
    Last edited: Feb 8, 2017
  4. KTW

    KTW

    273
    15
    Feb 22, 2015
    I discovered the problem, two different sensors.

    NTC thermistors decrease in resistance as the temperature increases. PTC thermistors are Positive Temperature Coefficient resistors generally made of polycrystalline ceramic materials that have a high positive temperature coefficient, which increases in resistance as the temperature increases
     
    CDRIVE likes this.
  5. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    That's equivalent to 100Ω to 200Ω. Is that a typo?

    Chris
     
  6. KTW

    KTW

    273
    15
    Feb 22, 2015
    No typo, 105 ohms ambient temperature.
     
  7. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
  8. KTW

    KTW

    273
    15
    Feb 22, 2015
    Hi Chris, thanks for your input.
    The probe that comes with the unit can sense temperature up to 110o C.
    The element I'm using gets to 85oC so I'm ok temperature wise but the conductors are plastic insulated and that's why I was looking for a probe with higher temperature insulation.
    What do you think about using fiberglass sleeving over the existing ntc probe?
     
    Last edited by a moderator: Feb 10, 2017
  9. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Unfortunately I don't think that will help. It won't prevent the existing low temp insulation from melting. Are you sure the insulation isn't Teflon?

    Chris
     
  10. KTW

    KTW

    273
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    Feb 22, 2015
    Not sure Chris, I contacted the seller but I'm doubtful if they would know.
    We'll see.
     
  11. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Test the insulation at the end of the two conductors with heat from your iron but not the tinned tip. You don't want to yuck it up if it melts.

    Chris
     
  12. KTW

    KTW

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    Feb 22, 2015
    Hi Chris, it melts pretty quick.
     
  13. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    Hi KTW, that's not good news. It befuddles me why a manufacturer would make an extreme temperature Thermistor that doesn't provide wire lead insulation (Temp: min - Max) comparable to the range of the Thermistor and Probe? Perhaps they intended the Probe head alone to be subjected to those temps?

    There was a recent topic along the same lines as yours. Let me see if I can find it.

    Personally, I'd like to see these things manufactured with Teflon insulation for each lead and jacketed with the high temp, I think it's (Fiberglass?) flexible weave.

    Chris
     
  14. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Found it!
    https://www.electronicspoint.com/threads/thermal-fuse-ghd-please-help.282559/
    Not a Thermistor but reading the last post pretty much sums it up. As I see it it's pretty much what I said in my last post. IE the entire assembly should be capable of withstanding (at least) the temp range of the probe.. and then some.

    Could you please post a sharp photo of the probe? Especially the rear end.

    Chris
     
  15. KTW

    KTW

    273
    15
    Feb 22, 2015
    Here Chris, couple from each end.
    ntc1.JPG ntc2.JPG ntc3.JPG ntc4.JPG
     
  16. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    648
    May 8, 2012
  17. KTW

    KTW

    273
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    Feb 22, 2015
    I just wrote to ask if it was ntc or ptc.
    Thanks for taking the time to find that, I did search earlier and couldn't locate one similar.
     
  18. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Yes, it's absolutely frustrating. I clicked on every damn link the seller provided regarding the specs. I thought for certain that the Newark link would certainly provide specs but it was a dry well. Even the pdf datasheet provided nada.
    http://www.farnell.com/datasheets/2015876.pdf?_ga=1.162269948.1387451233.1478563265

    This is one of those times that you might be well advised to deal with Digikey. They will match your needs via on line or phone call help.

    Chris
     
  19. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
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    May 8, 2012
    BTW, what is an emissions system smoker? Photos?

    Chris
     
  20. KTW

    KTW

    273
    15
    Feb 22, 2015
    Hi Chris;
    Let me say thanks for the effort you put into this.

    This is for a vehicle emissions leak test when the engine light comes on and tells you there is a small or large leak in the system.
    I'm chasing down a small leak in my wife's jeep.
    I plan on using the original nt probe for my initial test, it should work for locating the leak I'm chasing and I'll keep looking for something better suited to the heat.
    For a quick description, place an element in baby oil and let it reach a temperature where it will smoke.
    Apply very light air pressure and insert a plastic tube from the top of the can into the emission lines and watch for the smoke to appear to locate the leak.

    emissions tester.JPG

    emissions tester2.JPG
     
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