Patent ID: 7193187

Claim:
A method for controlling electrical heating of an element to maintain a constant electrical resistance R s , comprising: (a) supplying electrical power to said element in an amount sufficient for heating same and increasing its electrical resistance to R s , while concurrently monitoring real time electrical resistance R of said element for detection of any difference between R and R s ; (b) upon detection of a difference between R and R s , adjusting the electrical power supplied to said element by an amount ΔW determined approximately by: ( i ) Δ ⁢ ⁢ W = m α ρ × t × R 0 · ( R s - R ) ; or ( ii ) Δ ⁢ ⁢ W = m α ρ × t × R 0 · [ R s + R ⁡ ( 0 ) - 2 ⁢ R ] ; or ( iii ) Δ ⁢ ⁢ W = m α ρ × R 0 · [ f s ⁡ ( R s - R ) - R - R ⁡ ( 0 ) t ] , wherein m is the thermal mass of said element, α p is the temperature coefficient of electrical resistance of said element, R 0 is the standard electrical resistance of said element measured at a reference temperature, t is the time interval between current detection of electrical resistance difference and last adjustment of electric power, R(0) is the electrical resistance of said element measured at last adjustment of electric power, and f s is a predetermined frequency at which the adjustment of electric power is periodically carried out.