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Integrating preconcentrator heat controller

  • US 7,282,676 B1
  • Filed: 01/27/2006
  • Issued: 10/16/2007
  • Est. Priority Date: 01/27/2006
  • Status: Expired due to Fees
First Claim
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1. A method of controlling the resistive heating of a metallic chemical preconcentrator screen, comprising:

  • a) initiating a screen-heating pulse at time=0 by causing an electric current, Is to flow across a preconcentrator screen by applying a voltage drop, Δ

    Vs, across the screen from one edge of the screen to the opposite edge;

    wherein the screen has an in-plane electrical resistance Rs; and

    wherein the current is given by eq. (2a);


    Is

    V
    s/Rs



    (2a) 

    and wherein the voltage drop, Δ

    Vs, is given by eq. (2b);


    Δ

    Vs=IsRs



    (2b)b) increasing, during the heating pulse, the temperature of the screen by depositing internal Joule-type electric resistance heat energy directly in the screen;

    c) measuring, as a function of time, the voltage drop, Δ

    Vs, or the electric current, Is, or both;

    d) calculating, as a function of time, the heating power, PS (t);

    according to any of the following eqs. (3a), (3b), or (3c);


    Ps(t)=IsΔ

    V
    s



    (3a)
    Ps(t)=(Is)2Rs



    (3b)
    Ps(t)=(Δ

    Vs)2/Rs



    (3c)e) calculating the accumulated amount of heat energy, Es(t), deposited in the screen by integrating the heating power, Ps(t), over time from the beginning of the heating pulse (at t=0) up to the present time, t, according to eq. (4);


    Es(t)=∫

    Ps(t)dt



    (4)f) comparing, as a function of time, the accumulated heat energy, Es(t), to a pre-set target amount of energy, Etarget; and

    then either;

    g) continuing to heat the screen if Es (t)<

    c Etarget;

    orh) terminating the heating pulse if Es(t)≧

    Etarget, by stopping the flow of electric current, Is, across the screen;

    wherein the net temperature rise, Δ

    Ts, of the screen, from beginning to end of the heating pulse, is proportional to the total amount of resistance heat energy deposited in the screen during the heating pulse.

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