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Thread: Electric UFH + QAI How ?

  1. #1
    Automated Home Jr Member
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    Sep 2013
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    Default Electric UFH + QAI How ?

    Hi,

    I have electric UFH and am unsure how to connect the temp sensor to a QAI input. Do I just connect it to 0v and input 1 or do I need to connect it to a voltage and use an pull down resistor.

    The details on the temp sensor are a little sketchy. It's an NTC type and gives a reading of about 10k @ 25c. I have again contacted the company that makes it to get further details but I may have to try to figure this one out on my own.

    If I can get some sane readings from the QAI I will be able to figure out the rest as I can use the manufacturers thermostat to set the temp and to read the resistance at various temps. Just need help on how I should properly connect to the QAI input (I know that unused inputs should be connected to 0v).

    Thanks for the assist.

    Chris.

  2. #2
    Automated Home Legend Karam's Avatar
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    Mar 2005
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    You need to create a voltage divider at the QAI. The standard version QAI provides a 3.3V terminal. You connect your thermistor between the 3.3V terminal and the desired input channel and you connect a resistor between this input channel and the 0V termnal on the QAI. The resistor value suggested in this case is 10K. If you already have a QAI object in Cortex and have some inputs of this connected to (assigned to) analogue input signal sub objects then, if you pull up the behaviour menu for the analogue input signal object and click on the icon at the bottom which looks like a graph, this will bring up the scaling options for that input. You will notice that one such option is dedicated to the characteristics of NTC thermistors. Select this and you will see the connection diagram. Also it so happens the defaults are set for a 10K @25C sensor with 10K resistor divider. The beta value is dependent on the particular sensor. If you can get this from the manufacturer all the better, otherwise the default value should give you a good start.

  3. #3
    Automated Home Jr Member
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    Sep 2013
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    Hi Karam,

    Thanks for taking the time to respond. We had discussed this a while back and I didn't want to take up anymore of your time. I understand what I need to do now and have found the connection diagram you mentioned in the NTC scaling options. Much appreciated !

  4. #4
    Automated Home Jr Member
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    Sep 2013
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    Karam,

    Just connected it all up as per your recommendation and with a 10k resistor, getting good stable eadings of ~23.0c now. Bathroom temp air sensor is 25c according to Cortex so seems about right. Thanks again

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