An easy-to-build balance for automatic measurement

Abstract

The design and construction of a continuously recording precision balance resistant to varying pressure and temperature conditions and suitable for data acquisition systems is described. A horizontal beam is suspended at both ends by a pair of wires yielding a trapezoidal configuration. The horizontal displacement of the beam due to the difference of a probe mass acting on one beam end compared with a reference mass attached to the other end is tracked by an inductive displacement transducer. In order to bring the displacement to zero, a controller applies a horizontal electromagnetic compensation force on the beam proportional to the weight difference. The prototype achieved an overall accuracy better than 50 mg in the range 30-50 g at temperatures ranging from 20 to 100 degrees C. An integral-differential (ID) controller gives accurate and stable control. The time constant of the controlled balance was about 2 s.