Electronic balance with calibrating system

Abstract

In high-resolution electric balances a certain residual temperature coefficient remains even with a good correction of the temperature-dependent errors of the measured value sensor. The invention therefore is with respect to a balance with a built-in calibrating weight (standard) which responds with a new calibration switching in said calibrating weight if a given temperature changes has been exceeded since the last calibration. To this end, the balance comprises in microprocessor digital signal processing unit a separate memory area in which the output signal representing temperature value of a temperature sensor is stored during the calibrating process and also comprises a comparator which upon instruction compares the instantaneous output signal of the temperature sensor which the value stored in this separate memory area. If this difference exceeds a given amount, a signal element indicative of need to recalibrate using the calibrating weight is actuated. In addition, an elapsed time indicator can also be present which also actuates the signal element after the passage of a given time since the last calibration. In an advanced embodiment the apparatus will automatically cause recalibration to physically take place by having the signal processing unit control a motor which will switch the calibrating weight into weighing position. Said automatic recalibration taking place instead of or in addition to actuation of the signal element. Other physical science inputs can also be sensed and utilized by themselves or in combination in determining when recalibration should occur.