Patent ID: 7282676

Claim:
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, I s to flow across a preconcentrator screen by applying a voltage drop, ΔV s , across the screen from one edge of the screen to the opposite edge; wherein the screen has an in-plane electrical resistance R s ; and wherein the current is given by eq. (2a): I s =ΔV s /R s (2a) and wherein the voltage drop, ΔV s , is given by eq. (2b): Δ V s =I s R s (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, ΔV s , or the electric current, I s , or both; d) calculating, as a function of time, the heating power, P S (t); according to any of the following eqs. (3a), (3b), or (3c): P s ( t )=I s ΔV s (3a) P s ( t )=( I s ) 2 R s (3b) P s ( t )=(ΔV s ) 2 /R s (3c) e) calculating the accumulated amount of heat energy, E s (t), deposited in the screen by integrating the heating power, P s (t), over time from the beginning of the heating pulse (at t=0) up to the present time, t, according to eq. (4): E s ( t )=∫ P s ( t ) dt (4) f) comparing, as a function of time, the accumulated heat energy, E s (t), to a pre-set target amount of energy, E target ; and then either: g) continuing to heat the screen if E s (t)<c E target ; or h) terminating the heating pulse if E s (t)≧E target , by stopping the flow of electric current, I s , across the screen; wherein the net temperature rise, ΔT s , 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.