US 4,189,017 AGranted

Weighing apparatus including digitalization error correcting means

AssigneeMettler Instrumente AG

InventorsFelix Strobel, Rudolf Stocker, Werner Zumbrunn

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Abstract

An improved weighing apparatus of the electromagnetic load compensation type is disclosed, including a correction loop connected between the output terminal of the synchronizer and the input terminal of the pulse length modulator for varying the regulated load signal from the PID regulator to produce a corrected regulated load signal which compensates for digitalization errors produced by the synchronizer. In one embodiment, the correction loop includes an integrator circuit for superposing on the regulated load signal an inverted integrated error voltage the magnitude of which is a function of the operation of the synchronizer relative to the mark signals. In a second embodiment, the correction loop includes an integrator circuit that periodically applies to the regulated load signal a constant reference voltage of opposite polarity. Preferably, the reference voltage is applied simultaneously with the periods of supply of the compensation current.

Claims8

Dependent claims

In a weighing system of the electromagnetic load compensation type including

(a) a load compensation coil (12) connected with the movable weighing member;
(b) means for periodically supplying said coil with compensation current for periods of time that correspond with the magnitude of the applied load, including
(1) normally open compensating current switch means (26) for connecting said coil with a constant current source (26);
(2) signal generator means (16) associated with said movable weighing member for generating a position signal;
(3) regulator means (18) for regulating said position signal to produce a regulated signal (19) that is a function of the load to be measured;
(4) sawtooth voltage generator means (27) for producing a sawtooth voltage (21);
(5) pulse length modulator means (20) responsive to said regulated load signal and said sawtooth voltage for producing a train of control signals (25) the lengths of which correspond with the magnitude of the regulated load signal;
(6) means (24) for producing a series of timing mark pulses (23);
and
(7) synchronizer means (22) responsive to said timing mark pulses (23) and said control signals (25) for periodically closing said compensating current switch means;
and
(c) load indicating means (33) including counter means (31) for counting the timing mark pulses during the periods when said switch means is in the closed condition, thereby affording an indication of the magnitude of the applied load;
the improvement which comprises
(d) correction loop means for varying said regulated load signal to correct for digitalization errors produced by said synchronizer means.

11 more elements

Dependencies are inferred from the claim text.