| 摘要 |
In an object weighing system, apparatus for automatically adjusting the zero-reference value of a weight-representing signal to a desired value equal to that signal level which would produce an indication of zero weight by the system. To accomplish this, the absolute value of the signal is detected and applied to a voltage-to-frequency converter, the pulses from which are counted in an up/down binary counter only when no object is being weighed; the direction of count is controlled by a polarity-representing signal applied to the voltage-to-frequency converter. The instantaneous running count in the counter is applied to a digital-to-analog converter, to produce a correction signal of substantially the same magnitude as the amount by which the zero-reference value departs from said desired value. This correction signal is combined with the unadjusted weight-representing signal in the polarity to drive the zero-reference value toward said desired value. Between successive non-weighing intervals, the feedback loop through the automatic zero-correction circuit is held open, but the previously-attained count and correction voltage are maintained, so that the zero-reference value of the weight-representing signal is also maintained at the desired value during the weighing intervals. The same pulses used for the automatic zero correction are also counted during the weighing intervals by another counter to produce signals indicative of the weight of the object being weighed.
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