Temperature-corrected weighing apparatus having electromagnetic load compensation means

Claim 1

In a weighing apparatus of the electromagnetic load compensation type including (a) a stationary member (10) having means defining a stationary permanent magnetic field; (b) a movable load carrier (14) normally having an initial no-load position relative to said stationary member; (c) compensation coil means (12) connected with said load carrier for movement in said magnetic field; (d) means (16, 18) for generating an analog weight-responsive signal (V w ) as a function of the displacement of the movable load carrier from its initial no-load position relative to said stationary member; (e) first comparison means (20) for comparing said weight-responsive signal with a sawtooth waveform signal to produce a compensation output signal (V c ) including a plurality of pulses the lengths of which are a function of the magnitude of said weight-responsive signal; (f) means (26, 28) operable by said output signal for supplying compensation current to said coil means for periods of time corresponding with the lengths of said output signal pulses; and (g) load indication means for indicating the magnitude of the load applied to the load carrier, including a source of counting pulses (30), a counter (34), and means (24, 60, 32) for supplying a first train of said counting pulses to said counter for periods of times corresponding with the lengths of said compensation output signal pulses; the improvement which comprises: (h) means (48) for storing the weight-responsive count of said counter means; (i) temperature compensation means for supplying temperature-responsive pulses to a counter means as a function of variations in the temperature of the weighing system, said temperature compensation means including (1) means including a temperature sensor (54) mounted on said stationary member for producing a temperature-responsive analog signal (V t ); and (2) means for supplying a second train of counting pulses the number of which corresponds with the magnitude of said temperature-responsive analog signal; and (j) means (42) for processing the weight pulse count with the temperature-responsive pulse count to produce a temperature-compensated weight result.