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Math Help - Help With Linearisation

  1. #1
    Newbie
    Joined
    Jun 2009
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    Help With Linearisation

    Hi

    New here so sorry if this is not the info needed. but i really need some help!



    need to convert the following into something excel can work with
    except i fail to understand the where its like 2t or 3t, t = temp & R0 = 100

    is the t2 = squared & t3 = cubed or something else... its to do with Linearisation....

    Quote below:


    The principle of operation is to measure the resistance of a platinum element. The most common type (PT100) has a resistance of 100 ohms at 0 C and 138.4 ohms at 100 C. There are also PT1000 sensors that have a resistance of 25 ohms and 1000 ohms respectively at 0 C.
    The relationship between temperature and resistance is approximately linear over a small temperature range: for example, if you assume that it is linear over the 0 to 100 C range, the error at 50 C is 0.4 C. For precision measurement, it is necessary to linearize the resistance to give an accurate temperature. The most recent definition of the relationship between resistance and temperature is International Temperature Standard 90 (ITS-90).
    This linearization is done automatically, in software, when using Pico signal conditioners. The linearization equation is:
    Rt = R0 * (1 + A* t + B*t2 +C*(t-100)* t3)
    Where:
    A = 3.9083 E-3
    B = -5.775 E-7
    C = -4.183 E -12 (below 0 C), or
    C = 0 (above 0 C)
    For a PT100 sensor, a 1 C temperature change will cause a 0.384 ohm change in resistance, so even a small error in measurement of the resistance (for example, the resistance of the wires leading to the sensor) can cause a large error in the measurement of the temperature. For precision work, sensors have four wires- two to carry the sense current, and two to measure the voltage across the sensor element. It is also possible to obtain three-wire sensors, although these operate on the (not necessarily valid) assumption that the resistance of each of the three wires is the same.
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  2. #2
    Senior Member
    Joined
    Apr 2009
    From
    Atlanta, GA
    Posts
    409

    Clarity?

    Quote Originally Posted by HunBamy View Post
    need to convert the following into something excel can work with

    ...

    Rt = R0 * (1 + A* t + B*t2 +C*(t-100)* t3)
    Where:
    A = 3.9083 E-3
    B = -5.775 E-7
    C = -4.183 E -12 (below 0 C), or
    C = 0 (above 0 C)
    Excel can work with this equation, R(t)=R_0(1+At+Bt^2+C(t-100)t^3) . What exactly is your question?
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