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strap on temperature vs thermowell

ratio
ratio Member Posts: 3,605
In the not too distant future, I want to instrument some heating pipes, up to about 3" size. Ideally I'd put in wells, but I'm pretty sure that'd add a lot to the price. How do the clamp-ons compare regarding accuracy & response time?

I've recently instrumented a few AC systems with k-type thermocouples stuck into the pipes with a dab of solder as an experiment. They seem to work fine, but I don't know how long they'll last. Any reason to not do this to black iron?

Comments

  • bob_46
    bob_46 Member Posts: 813
    If you are using thermocouples I would clean the pipe with sand cloth and fasten it with a hose clamp and insulate .
    bob
  • ratio
    ratio Member Posts: 3,605
    The easiest thing I've come up with is what I mentioned earlier: a "homemade" k-type, nothing more than a few twists in the end of the wire, stuck into the solder (15% Ag) while it's still wet. The 15% doesn't adhere to the thermocouple wire, but it seems to be mechanically sound, & should be about as thermally conductive as it gets. If the whole piping system is insulated, about what kind of lag might I expect, any guesstimate?
  • Gordy
    Gordy Member Posts: 9,546
    edited January 2016
    With copper pipes I have found a cheap simple indoor/outdoor thermometer using the outdoor probe to be quite effective as a strap on. I carefully remove the plastic sheath that houses the sensor wires this increases the sensitivity. Couple wraps of electrical tape, and insulation.

    Find ones with frequent sampling rates. Some read every 3 seconds. Check them together at different temps for accuracy to one another. I like the minimum /maximum temp logging that is resettable. If your looking for deltas over a period, or max/ min temps over a period.

    One con is they usually only go as high as 158* so for radiant they are fine. For high temp emitters not so much.
  • hot_rod
    hot_rod Member Posts: 21,858
    My experience is the response is about the same if you are talking copper pipe vs. in a well. Insulate and use some thermal grease to make sure you have good contact, for strap on thermistors.

    As Hatt mentioned, it depends how quickly you want the changing temperatures to read. The outside of the copper tube will get to the same temperature as the fluid if insulated properly.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • SWEI
    SWEI Member Posts: 7,356
    If you can make a 3/8" well ID work for you, the Pasco 1449-C and 1450-W generally cost less than $10 apiece.
    Rich_49
  • ratio
    ratio Member Posts: 3,605
    Thanks, I'll look into these.