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Thread: Thermometer - Range/Accuracy/Direct Contact?

  1. #1
    FLAC
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    Oct 2006
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    Las Vegas
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    1,286

    Thermometer - Range/Accuracy/Direct Contact?

    I think somewhere buried in one of these threads is my answer. I think I know which one, but I can't seem to find it there either.
    So:

    What is the min/max range of your thermometers?

    What is the accuracy?

    Will I physically be able to get a direct-contact, metal temp reading with it?

  2. #2
    Fusion Brain Creator
    Join Date
    Mar 2005
    Posts
    2,221
    MCP9700. They're good for -40C to 125C, with accuracy of about 2C. I've taken them to high emperatures than 25 and they seem accurate, but we don't guarantee that.

    Yes, direct contact is fine, just superglue or epoxy or clamp it on.

  3. #3
    Newbie
    Join Date
    Jul 2007
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    39
    I currently have 3 temp sensors connected, and they all have the same reading of 67.209 degrees. They are in different parts of my house, so I would expect different readings.

    I placed a temperature/humidity data logger next to one of them, and that reported a temp of 64.1 degrees, so at least one temp sensor is off by a significant amount.

    Thoughts?

  4. #4
    Fusion Brain Creator
    Join Date
    Mar 2005
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    2,221
    The temperature sensors are rated to +/- about 2C, which is +/- 4deg F.

    Additionally, your house is probably pretty similar in temperature, most parts of a house are within 1 degree of each other.

    The Fusion Brain is not designed to be a precision measurement device.... Most precision temperature sensors cost several hundred dollars.

    You could improve accuracy with an op-amp to amplify the temp sensor's signal, but that would reduce it's effective range.

  5. #5
    Fusion Brain Creator
    Join Date
    Mar 2005
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    2,221
    After seeing AtomicMonkey's issues here, I decided to look more into the issue.

    As it turns out, some of the ADC (analog to digital converter) values are not set uniformly from the factory. They are stored in registers that can have different default values depending on the manufacturer. This caused small errors in some boards, perhaps including yours, and large errors in recent boards (Shipped mid-January and later).

    I have recoded the relevant parts of the firmware, and have the following:


    As you can see, I hooked up a ton of temperature sensors, 12 at first:


    Displayed are the raw voltages. Converted, they are as follows:
    Code:
    Raw Volts	deg F
    
    0.879765	76.286
    0.869990        75.38369231
    0.879765	76.286
    0.889541	77.1884
    0.889541	77.1884
    0.874878	75.83489231
    0.874878	75.83489231
    0.899316	78.09070769
    0.889541	77.1884
    0.889541	77.1884

    And then, to address AtomicMonkey's problem, here is a picture of 9 thermometers and one variable resistor set at ~3.95vDC.

    If you are affected by this, we offer two options, both of which can be arranged over our email account:

    1.) Buy a new PIC from us. $12 shipped.
    2.) Exchange PICs. Send us $6, and we will send you a new PIC. Once we get your old PIC back, we refund you.
    3.) Send back your PIC, and we'll send you a new one.

    All orders shipped on or after 2/19/2008 will not have this problem.

  6. #6
    Newbie
    Join Date
    Feb 2009
    Location
    Melbourne, Victoria, Australia
    Posts
    20

    wrong temperature being displayed

    Hi I just got a temp sensor from you and then followed your tutorial on Youtube ([media]http://www.youtube.com/watch?v=xQ-nINroIRE[/media]).

    When I start it up I get a Voltage of 1.0 and a current temp of 34 (celsius - im in australia).

    This sensor is inside my house and sitting next to a digital thermometer that is currently showing 22.9.

    what am I doing wrong?

    Thanks

    PS I did NOT add the farenheit conversion to my confige as it is not needed.
    PPS I am using a Version 3 Brain

  7. #7
    Fusion Brain Creator
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    Mar 2005
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    2,221
    Does the value change with temperature?

    Can you upload a picture of how you have it connected?

  8. #8
    Newbie
    Join Date
    Feb 2009
    Location
    Melbourne, Victoria, Australia
    Posts
    20


    Here is a picture, its rather blurry but the best I can get with my camera phone.

    The temperature has changed (its currently reading 33.5 Deg Celsius) but the Voltage has remained the same at 1.0.

    Cheers

  9. #9
    Fusion Brain Creator
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    Mar 2005
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    2,221
    Picture's not loading for me here.

    Can you heat/cool the probe (with ice, or something warm) and let me know what happens?

  10. #10
    Newbie
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    Feb 2009
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    Melbourne, Victoria, Australia
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    20
    I have heated it and the temperature does change.

    I have tried attaching a link to the photo again.

    <a href="http://s441.photobucket.com/albums/qq138/pokersoft/?action=view&current=FusionBrain.jpg" target="_blank"><img src="http://i441.photobucket.com/albums/qq138/pokersoft/FusionBrain.jpg" border="0" alt="Photobucket"></a>

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