Heating pipe temperature sensor

Discussion in 'The Projects Forum' started by mpooley, May 2, 2010.

  1. mpooley

    Thread Starter Active Member

    Mar 3, 2010
    35
    0
    hi folks this is my first post here so I hope this is the right place.
    I have two questions.
    1: is there a digital sensor similar to the DS18S20 High Precision 1-wire Digital Thermometer that is more suitable to bond with a hot water pipe?

    2: I have a atmega 328 which inputs would i use for 2 of these sensors?

    thanks very much for all replies

    Mike:confused:
     
  2. AlexR

    Well-Known Member

    Jan 16, 2008
    735
    54
    If you are talking about domestic hot water then the DS18S20 or DS18B20 will be fine. The maximum temperature they can measure is 125°C while most hot water systems run at 65°C to 70°C and hopefully the water/pipe temperature will never get anywhere near 100°C. Just clamp or superglue it to the pipe.
     
  3. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Pretty much any digital IO line out of the ATMEGA328 can be used to communicate over the Dallas 1-wire interface. Just keep in mind that you will need to change the direction of the digital IO pin from input to output as you read or write to the 1-wire device.

    hgmjr
     
  4. spacewrench

    Member

    Oct 5, 2009
    58
    1
    I have a radiant floor system that I monitor with DS18S20s. On the (copper) input & output pipes, I just taped the sensors to the pipes with aluminized duct tape. They seem to work well, at least compared to IR thermometer readings of the same pipes.
    You can run multiple sensors off each GPIO line. (I have 5 on one of my ARM I/O lines.) If you're using parasite-power mode, don't forget to switch the GPIO line to output, active high after you issue the "measure temperature" command. And wait 750ms for the measurement to complete!
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Keep in mind that most water pipes are PVC (or CPVC for hot water); and being plastic, they don't have really great thermal characteristics.

    If you want your readings to be reasonably accurate, you need both a good thermal bond to the pipe, and insulation over and around the sensor to keep ambient air from cooling the area.
     
  6. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    Sgtwookie has a good point above about the thermal conductivity of PVC plastic water pipes. If you need greater thermal compliance you could splice a short piece of copper pipe in the line and attach your temperature measuring device to the copper.

    hgmjr
     
  7. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
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    Also remember, place the sensor BELOW the 9 o'clock position. It you put the sensor at 12 o'clock, and there is and air in the line, i.e. the pipe isnt 100% full, you will get an incorrect reading.

    6 o'clock is the best.
     
  8. mpooley

    Thread Starter Active Member

    Mar 3, 2010
    35
    0
    Ok Thanks to you all.

    I have an all copper system so no problems there. the black tape idea is nice and I will probably glue and tape them in position now.

    so thanks once again for your help :)

    Mike
     
  9. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    Also keep the first few inches of the connecting wire or cable in thermal contact with the pipe - if the wire is at (or nearer) ambient temperature, it will act as a heatsink for the sensor IC and throw off the readings.
     
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