Simple capacitive sensors for mass measurements

Design and operation of two simple capacitive transducer systems are described here. The first design uses a spring for the air-gap variations of a capacitor, while the second one employs a cantilever steel beam as a restoring element in a capacitive transducing arrangement. The reported setup makes it possible to detect mass changes of the order of 0.1 g in a 250 g range. A comparison has been made between the results of two sensors, and the second design shows a better performance in terms of repeatability, linearity, and sensitivity. It has a repeatability of better than 4% for this range of operation. This device is suitable for mass measurements of medium resolution and dynamic range and has the advantage of simplicity in design and construction.