Rctime and ntc


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Thread: Rctime and ntc

  1. #1

    Default Rctime and ntc

    Hi, I'm Cristian, I tried to use BASIC pic to read the value of a NTC with RCTIME command but do not know how to convert that value in degrees. Could you help me? I used a ntc 10k and a capacitor 100nf, I tried to do a reading at 27 degrees and 128 with me RCTIME command.
    How can I convert that value.
    Thanks in advance
    Greetings

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    Default Re: Rctime and ntc

    Wow, having never used RCTIME I am flying by the seat of my pants here (as Usual), but you are able to approximate the resistance (you do the math) of your NTC and from there I would make a lookup table to output the value, based upon the specs of the thermistor (published table?) and your own recorded values. For instance if your RCTIME results are 1200 and your NTC is 200 F and it if it is 600 @ 32F then you can start that table. Again compare how your results track the published specs.
    I tried to do a reading at 27 degrees and 128 with me RCTIME command.
    How can I convert that value.
    compare your readings & subtract, multiply or divide the difference by 101/100
    Last edited by Archangel; - 22nd October 2013 at 03:06.
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    Default Re: Rctime and ntc

    Ok thanks for your response. I made a table and I got 367, 6 ° C and 67 ° C with 80 now you suggest I split the valiri for 101 or 100? I did not understand. sorry but I write with a translator because I'm Italian. hello

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    Default Re: Rctime and ntc

    the 100 & 101 are percent based upon your sample spread what you need is the ratio of reading per degree, you can divide it or use a lookup table. The lookup table is more tedious but can be adjusted to calibrate results. The numbers I got were 287 & 4.377, 4.377 per degree. Round it up to 4.38
    multiply everything by 100 and divide. Check div32 function.
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    Default Re: Rctime and ntc

    since I am a beginner can you please explain step by step how you did to get that value. hello thanks

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    Default Re: Rctime and ntc

    Sure, 67 - 6 = 61 hi temp - lo temp
    367 - 80 = 287 hi reading - low reading
    287 / 61 = 4.7049180327868852459016393442623
    so round off to 4.70 ratio per degree
    appears my 4:00 am math was a little skewed
    If you do not believe in MAGIC, Consider how currency has value simply by printing it, and is then traded for real assets.
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    Default Re: Rctime and ntc

    so I have to grades I should take the value derived from RCTIME, for example 367, and divide it by 4.7 and then obtain the degree? because if it does not come out a correct value. I'm sorry the disorder

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    Default Re: Rctime and ntc

    Quote Originally Posted by larosacristian View Post
    so I have to grades I should take the value derived from RCTIME, for example 367, and divide it by 4.7 and then obtain the degree? because if it does not come out a correct value. I'm sorry the disorder
    PBP's aversion to decimal math, you need to convert to integer math, in this case, multiply everything by 100 and violla integer math.
    If you do not believe in MAGIC, Consider how currency has value simply by printing it, and is then traded for real assets.
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    Default Re: Rctime and ntc

    thanks again, that you say, 367x100 = 36700/4.7 = 7808/100 = 78 but I have to get 6 ° C not 78 what is wrong?

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    Default Re: Rctime and ntc

    You know what? It's not going to be linear anyway, so don't lose too much sleep over it.
    “Steinhart-Hart” is something to google, it looks like thermistors make a big "S" curve on a graph.
    Here is a link to thermocouple chart for the common K type thermocouple, see if you can find something similar for your particular thermistor
    so you do not have to make your own.
    BTW what are you making here anyway, and how critical are the readings ?

    Check these 2 threads:
    http://www.picbasic.co.uk/forum/showthread.php?t=14216
    http://www.picbasic.co.uk/forum/showthread.php?t=14008
    Last edited by Archangel; - 23rd October 2013 at 11:19.
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    Default Re: Rctime and ntc

    NTC are negative termoresistor. Which means that while temperature increases resistance of the termistor decrease, so they are inversely proportional.

    Al.
    All progress began with an idea

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    Default Re: Rctime and ntc

    RE: Yes it does but it does not mean they are linear, which is why I do not think simple division will have accuracy.
    If you do not believe in MAGIC, Consider how currency has value simply by printing it, and is then traded for real assets.
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    Default Re: Rctime and ntc

    thanks for the answers, I do not need to be precise I just have to control the switching on and off at a given temperature a fan then, that there is an error of a degree I do not care.
    Last edited by larosacristian; - 23rd October 2013 at 21:12.

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    Default Re: Rctime and ntc

    Of the one specific thermistor I looked I downloaded the excel file and from 0 degree to 100 degree the curve is indeed exponential. I tried to import the data into excel but I've forgotten how to get it to give you a formula to fit the data entered. I browsed a few others and they all look about the same but you can find the math for a precise formula at http://www.epcos.com/web/generator/W...dardizedRT.pdf. Putting that into PBP will be a challenge to say the least.

    This site though has a much easier formula if you know a little of your thermistors' data:http://www.mstarlabs.com/sensors/the...libration.html

    Though I thought this site gave you a better idea of how to find the right formula:http://www.cantherm.com/products/the...osing_ntc.html

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    Default Re: Rctime and ntc

    thank you very much I will try to set formulas in pbp and let you know. thank you very much. if someone already has some sample code that can assist me I would be most grateful if you would provide me. greetings

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