Importance

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Abstract

An apparatus for inspecting a coating formed on a workpiece, comprising a light emitter and a light receiver positioned on respective sides of the workpiece; an amplifier for amplifying a detection signal from the light receiver and for generating an amplified output signal; a comparator for comparing the amplified output signal with a predetermined level thereby to generate a control signal indicative of a difference between the amplified output signal and the predetermined level; a zero adjustment for adjusting the amplified output signal to a zero value; and a tuning circuit for tuning the amplified output signal, which is generated from the amplifier when the workpiece to be inspected has not yet been formed with the coating, to a predetermined tuned value. The tuning circuit is operable to vary the amplification factor of the amplifier and also to the intensity of light emitted by the light emitter. In place of the tuning circuit, an amplification factor setting citcuit may be used for sampling the light transmissivity of the workpiece and for selecting one of amplification factors according to the result of sampling. After the formation of the coating on the workpiece, the amplified output signal may decrease with a decrease of the light transmissivity of the workpiece, and the coating condition is determined depending on whether or not the amplified output signal is lower than the predetermined level.

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First Claim