Chemical milling−Determination of depth and rate of etch based on sacrificial dissolution of one arm of a ratiometric transducer

Abstract

The change in electrical resistance during the chemical dissolution of one arm of a variable ratio potentiometric bridge under constant current conditions is shown to offer a high precision, high resolution method of determining depth and rate of etch in immersed alloy work pieces undergoing chemical milling. The method is stable and repeatable, displaying negligible interference or disturbances due to electrochemical or electrothermal e.m.f.’s. Solution shunt conductivity is shown to have no significant effect on measurement accuracy allowing the sacrificial test piece to directly resolve etch depths to better than 10−5 m (10 μm) with comparable measurement of etch depth in the work piece. The principle is reliable and permits rugged construction, making it ideal for an industrial environment.