Electromagnetic force compensation scale with temperature compensation

US4300647A · kind A · utility

Assignee

• Sartorius AG · DE

Inventors

• Erich Knothe · Bovenden, DE
• Franz-Josef Melcher · Hardegsen, DE
• Jurgen Ober · Hardegsen, DE
• Lothar Behrend · Gleichen, DE

Key dates

• Filing date: Jul 23, 1980
• Grant date: Nov 17, 1981
• Expiry date: Jul 23, 2000

Classification

• Technology area (CPC G): Physics
• CPC primary: G01G19/414
• WIPO field: Measurement
• WIPO sector: Instruments

Abstract

A scale of the electromagnetic force compensation principle, having a stationary permanent magnet system with an air gap and at least one coil positioned in the air gap, the coil being acted upon via a position sensor and a variable-gain amplifier by a compensation direct current dependent on the load of the scale, wherein the compensation direct current flows through a measuring resistor from both ends of which a signal dependent on the load of the scale is tapped off and fed to an analog/digital converter, and further electric circuits are connected therewith which permit an alternating current to flow, in addition to the compensation direct current, through the coil and the measuring resistor and including a regulating or adjusting device which modifies the amplitude of the additional alternating current in such a manner that the joulean heat generated in the coil and in the measuring resistor by the compensation direct current and by the additional alternating current is at least approximately load-independent.