Patent ID: 6715348
Filing Date: 2004-04-06
Classification: G01F,H01L

Abstract:
An apparatus for detecting the level of a processing liquid in a processing tank, comprising:a hollow sensor tube having an open distal bottom end positioned at a first position in the tank and adapted to be immersed in the processing liquid; gas supply means for supplying gas, having a pressure substantially greater than a pressure prevailing over an upper surface of the processing liquid, through the sensor tube to sufficiently fill the interior thereof entirely to the open distal bottom end; a detecting sensor for providing an output signal representative of the gas pressure within the sensor tube; a determination circuit, that comprises a high-pass filter for extracting any alternating component in said output signal to generate an AC signal and a signal processor for rectifying the AC signal from the high-pass filter, for determining when the liquid level reaches the first position established in the tank on the basis of said output signal from said detecting sensor; a liquid level detecting circuit for correcting a relationship between a level of said output signal from said detecting sensor and the liquid level on the basis of a signal generated by said detecting sensor from the time the processing liquid is initially supplied to the tank until immediately after the liquid level reaches the first position to thereby detect the liquid level in the tank.