Servo-Controlled High-Accuracy and Low-Cost Electronic Scale
Original Publication Date: 1987-Dec-01
Included in the Prior Art Database: 2005-Feb-02
This article describes a design for a laboratory scale that allows a high degree of accuracy by use of a closed-loop servo system. This causes certain kinds of errors to be self-cancelling, thereby allowing the use of lower cost parts, while still maintaining accuracy. Referring to Fig. 1, the scale works on the principle that if the beam is brought back to the same position whenever the weight on the scale pan is changed, the force necessary to do this can be measured. In this design, force is provided by a solenoid pulling down on the beam. To detect the scale 'balanced' position, an optical position sensor is used. Optical position sensors (OPSs), while not perfectly linear, exhibit very good zero repeatability, which is all that is necessary in this application.