Temperature-compensated magnetoelastic force measuring means

A magnetoelastic force measuring device operating during successive, measuring and calibrating periods and with temperature-compensated sensitivity, comprising:

• a measuring transducer having a core with a measuring portion, an excitation winding adapted to be supplied with an alternating power supply, and a measuring winding;
• a reference transducer having a core of the same material as said measuring transducer and a measuring portion with an excitation winding and a measuring winding, said reference transducer measuring portion having substantially the same planar shape and dimensions as said measuring transducer;
• said reference transducer being mounted in thermal contact with said measuring transducer, the excitation windings of said measuring and reference transducers providing the measuring portions of both transducers with the same excitation;
• spring means for loading said reference transducer measuring portion with a constant force;
• an amplifier supplied alternatively with the output signal from said reference transducer during the calibration periods and the output signal from said measuring transducer during the measuring periods;
• a phase-sensitive rectifier responsive to the output of said amplifier;
• means for supplying a phase-shifted control voltage to said phase-sensitive rectifier with the same frequency as the excitation of both the measuring and reference transducers;
• a difference generator having a first input receiving the output signal of said rectifier during the calibration periods and generating a difference signal output, and including a second input;
• a reference voltage source supplying a reference voltage to said second input;
• an integrator for integratiang said difference signal output, the integrated difference signal controlling said phase-sensitive rectifier to equalize the output thereof with said reference voltage, said integrator having a long discharging time compared to a measuring period so that the phase position of the control voltage, obtained during one calibrating period, is maintained for the next measuring period;
• and
• switching means for connecting, during the calibrating periods, an output signal of said reference transducer to said amplifier, and simultaneously connecting the rectifier output to said first input, and connecting, during the measuring periods, an output signal of said measuring transducer to said amplifier, and simultaneously connecting said rectifier output to a digital voltmeter for indicating the temperature-compensated value of the force acting on said measuring transducer.