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soldering iron tip vs multimeter temperature probe

Discussion in 'General Electronics Discussion' started by gcb, Jun 16, 2012.

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  1. gcb

    gcb

    32
    0
    Mar 26, 2012
    got a cheap chinese 75w soldering station that claims to be adjustable for 200C to 500C.

    first thing i did when i got it was to test the tip temperature with my multimeter.

    it's a fluke 87V with the original temperature probe.

    I turn the iron ON to 250C. The station has a red led when it's heating and a green when it's stable. It gets to green in a matter of seconds. Touching the 60/40 solder melts it in less than half second of contact

    but touching the temperature probe... the multimeter will rise to 150C on the display in a few seconds, and then rise extremely slowly... two minutes and it's on 157C... if i untouch it and rapidly touches again, it will show 140C and stay on the slow climb... untouch and touch again... 130C... one minute later it raised to 145C... but.. wasn't it 157C just now? and it's still melting the solder.

    so, it's not possible to test soldering iron temperature with an expensive multimeter temperature probe? or am i doing something dumb?
     
    Last edited: Jun 16, 2012
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    10,069
    2,150
    Nov 17, 2011
    The temperature probe may draw too much heat from a small solder tip. Or the thermal contact between tip and probe is bad, thus transferring not enough energy to the probe.
    In contrast once the solder starts melting it will cover the solder tip and thus help to transfer more energy to melt the rest of the solder.

    Harald
     
  3. shrtrnd

    shrtrnd

    3,744
    482
    Jan 15, 2010
    It's probably the way the soldering iron is grounded, compared to what the meter is grounded to. Test and measurement instruments are funny about how their circuitry is
    designed to take readings. A lot of times we don't think about how the circuitry under
    test is affecting the T&M instrument.
     
  4. gcb

    gcb

    32
    0
    Mar 26, 2012
    indeed. Thanks to brands like fluke that does not provide schematics

    should I try to isolate the contact adding a insulation tape that can stand 800C?
     
  5. gcb

    gcb

    32
    0
    Mar 26, 2012
    any less destructive idea to transfer heat to the sensor that does not involve dipping it in a blob of solder? :)
     
  6. gcb

    gcb

    32
    0
    Mar 26, 2012
    What's this thermal cement he uses here

    can i use something like "heatsink glue" to attach my multimeter temp probe to the iron?
     
  7. Harald Kapp

    Harald Kapp Moderator Moderator

    10,069
    2,150
    Nov 17, 2011
    I don't think "heatsink glue" can withstand these temperatures.You'd have to look it up in the specs of the material you want to use.

    Harald
     
  8. shrtrnd

    shrtrnd

    3,744
    482
    Jan 15, 2010
    I hope this isn't some type of critical lab measurement.
    You sound pretty serious about wanting to read the temperature here.
    I'd find myself a small piece of ceramic, put the temp probe on one side, and the
    soldering iron tip on the other side.
    The sensor and the tip would be electrically isolated, and the heat should transfer within
    a short period of time.
    I'm just telling you this if this is some type of a curiosity thing.
    If you're trying to get an accurate reading for some work or lab project, you will lose
    some heat simply because the ceramic will act as a heat sink and dissipate some of
    the heat being cooled by the ambient air around it. You'd have to take special
    precautions for a laboratory test.
    All things considered though, I think you'd get a good ballpark figure this way.
    I'd look for as thin a ceramic film as I could find. They were pretty common in old
    electronic gear, I've got a small drawer full of scavanged ceramic and mica.
     
  9. gcb

    gcb

    32
    0
    Mar 26, 2012
    i will try that as soon as i find something that could work. good idea.

    the problem is just that I bought one chinese soldering station (75W, brand AOYUE) and my soldering got worse (it was already bad) and since i only used it after the time i had to return, i'm tempted to throw it in the garbage every time i have to use it... thankfully it's extremely rare. but when i have to use it, it's on some sensitive or even SMD thing... which usually i only have one lying around

    i adjust the damn thing to 300C or 350C (goes from 200C to 480C) and it has problems melting 60/40 solder, at 300C it will never melt solder if a fan is blowing over it (that's my fume extractor :). at 350C and it's impossible to use a desoldering wick... i just press it there for half an hour and nothing happens, not even rosin core smoke. always have to use it at max
     
  10. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    Well putting any potential issues with the iron not performing properly aside, my I suggest you reverse the fan so that you are slightly pulling air over the work area vs directly blowing air on the work area... This will make a world of difference in maintaining heat, trust me...
     
  11. shrtrnd

    shrtrnd

    3,744
    482
    Jan 15, 2010
    What's the condition of your solder tip?
    What you're describing is what happens to my iron when the solder tip needs to be
    retinned (Sal Amoniac, or some of those small tins for retinning tips at the local electronics
    store).
    If the solder tip is gummed-up, it doesn't transfer the heat very well from the solder
    tip to the solder, and the solder doesn't melt.
    Just one other thing to look at, while you're trying to get back to normal work.
     
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