Zero tracking circuit for electronic weighing scale

A circuit for digitally displaying the magnitude of an input analog signal comprising a source of clock pulses, means for generating a timing signal proportional to the instantaneous magnitude of the input signal, resettable up-down counter means responsive to the timing signals for successively upcounting and downcounting clock pulses and means responsive to said timing signal for latching an output count of said counter means;

• decoder means for monitoring the output count at a time whereat said count is proportional to the input signal magnitude;
• means for displaying said output count at said time and means responsive to said decoder means for resetting said counter means when said output count at said time has a value that is characteristic of drift,
• said resetting means including means responsive to said decoder means for generating reset pulses identifying a low magnitude counter output characteristic of drift, accumulator means for accumulating said reset pulses and means responsive to a predetermined number of reset pulses in said accumulator means for resetting said counter means.

In a weighing scale of a type comprising a transducer for developing an analog signal proportional to magnitude of an applied weight to be displayed in a display, a source of clock pulses;

• analog to digital converter means for converting the analog weight responsive signal to a corresponding digital signal and means for displaying said digital signal;
• said converter means including means for sampling the analog input signal means for generating timing pulses having interpulse spacing proportional to analog signal magnitude, resettable counter means, means for controlling said counter means to successively upcount and downcount said clock pulses, and means responsive to said timing signals for latching an output count in said counter means at a display time whereat said count is proportional to the magnitude of an input analog voltage sample, and means for resetting said counter means:
• a zero tracking method comprising the steps of monitoring the output of said counter means at the display times, generating a reset pulse when the monitored count has a magnitude corresponding to drift, accumulating said reset pulses and resetting said counter means upon accumulation of a predetermined number of said reset pulses.

A method of zero tracking in a dual slope type analog to digital converter, said converter including means for sampling the input analog signal, integrator means responsive to the analog signal samples for generating control pulses having interpulse spacings proportional to input analog signal magnitude, up-down counter means;

• clock means, means controlled by said control pulses for accumulating numbers of pulses generated by said clock means proportional to input analog signal magnitude, means for resetting said counter means, and display means for displaying contents of said counter means, comprising the steps of monitoring pulse counts applied by said counter means to said display means;
• detecting a low magnitude pulse count that is characteristic of drift and, in response, generating a reset pulse, accumulating said reset pulses and resetting said up-down counter means upon accumulation of a predetermined number of said reset pulses.

A circuit fo digitally displaying the magnitude of an input analog signal comprising a source of clock pulses, means for generating a timing signal proportional to the instantaneous magnitude of the input signal, resettable up-down counter means responsive to the timing signals for successively upcounting and downcounting clock pulses and means responsive to said timing signal for latching an output count of said counter means;

• decoder means for monitoring the output count at a time whereat said count is proportional to the input signal magnitude;
• means for displaying said output count at said time and means responsive to said decoder means for resetting said counter means when said output count at said time has a value that is characteristic of drift, further including means for isolating the counter means and display means and responsive to said decoder means for zeroing said display means independently of said counter means during resetting of said counter means by said resetting means to prevent a count corresponding to drift from being displayed by said display means.

A method of zero tracking in a dual slope type analog to digital converter, said converter including means for sampling the input analog signal, integrator means responsive to the analog signal samples for generating control pulses having interpulse spacings proportional to input analog signal magnitude, up-down counter means, clock means, means controlled by said control pulses for accumulating numbers of pulses generated by said clock means proportional to input analog signal magnitude, means for resetting said counter means, and display means for displaying contents of said counter means, comprising the steps of monitoring pulse counts applied by said counter means to said display means;

• detecting a low magnitude pulse count that is characteristic of drift and, in response, resetting said up-down counter means, including the step of zeroing said display independently of said counter means during said resetting step to prevent a count corresponding to drift from being displayed by said display means.