Patent ID: 6318168
Filing Date: 2001-11-20
Classification: G01F

Abstract:
A thermal dispersion device, comprising:a reference temperature sensor for producing a first electrical signal representative of the temperature of a medium in which said reference sensor is immersed;a heating element;a constant power source connected to said heating element;an active temperature sensor located proximate said heating element for producing a second electrical signal representative of the temperature of said medium proximate that in which said active sensor and said heating element are immersed;a constant current source connected to each said active and reference sensor for applying a constant current thereto;means for receiving said first and second electrical signals and producing a thermal signal representative of the difference in the magnitude of said first and second electrical signals; andcircuit means responsive to the magnitude of said thermal signal for controlling the amount of heat produced by said heating element so as to maintain the difference between said first and second electrical signals between predetermined upper and lower limits, said circuit means including:switch means in series with said heating element and being responsive to a pulse width modulated control signal having a duty cycle for cyclically activating and de-activating said heating element;first and second amplifiers for amplifying said thermal signal and second electrical signal, respectively;means for digitizing said thermal signal and said second electrical signal; anda microprocessor for receiving digitized thermal and second electrical signals and generating said pulse width modulated control signal, said microprocessor being operative to incrementally increase the duty cycle of said pulse width modulated control signal when said difference falls below said lower limit and incrementally decrease said duty cycle of said pulse width modulated control signal when said difference rises above said upper limit.