Integrating preconcentrator heat controller
First Claim
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=Δ
Vs/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
Vs
(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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Accused Products
Abstract
A method and apparatus for controlling the electric resistance heating of a metallic chemical preconcentrator screen, for example, used in portable trace explosives detectors. The length of the heating time-period is automatically adjusted to compensate for any changes in the voltage driving the heating current across the screen, for example, due to gradual discharge or aging of a battery. The total deposited energy in the screen is proportional to the integral over time of the square of the voltage drop across the screen. Since the net temperature rise, ΔTs, of the screen, from beginning to end of the heating pulse, is proportional to the total amount of heat energy deposited in the screen during the heating pulse, then this integral can be calculated in real-time and used to terminate the heating current when a pre-set target value has been reached; thereby providing a consistent and reliable screen temperature rise, ΔTs, from pulse-to-pulse.
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Citations
22 Claims
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1. A method of controlling the resistive heating of a metallic chemical preconcentrator screen, comprising:
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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=Δ
Vs/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
Vs
(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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An integrating preconcentrator heat controller (IPHC) for controlling the resistive heating of a metallic chemical preconcentrator screen, comprising:
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trigger means for starting a screen-heating pulse at time=0 by causing an electric current, Is to flow across a preconcentrator screen in response to a voltage drop, Δ
Vs, applied 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 screen-heating current is given by eq. (2a);
Is=Δ
Vs/Rs
(2a)
and wherein the voltage drop, Δ
Vs, is given by eq. (2b);
Δ
Vs=IsRs;
(2b)means for measuring, as a function of time, the voltage drop, Δ
Vs, or the electric current, Is, or both;power-calculating means for 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
Vs
(3a)
Ps(t)=(Is)2Rs
(3b)
Ps(t)=(Δ
Vs)2/Rs
(3c)integration means for 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)comparison means for comparing, as a function of time, the accumulated heat energy, Es(t), to a pre-set target amount of energy, Etarget, and for deciding to continue heating the screen if Es(t)<
Etarget;
or to terminate 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. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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Specification