AN ELECTRONIC BALANCE

摘要

The weight W is weighed by measuring the current necessary in the coil 4 moving in the magnetic field of a yoke 2 to counteract the weight. The current is periodically switched between positive and negative directions at a rate which does not cause oscillation of the pan 3. A sensor 7 determines the position of the pan 3 and the output of the sensor controls the switching of the current to vary either the relative durations t1 and t2 or the relative magnitudes I1 and I2 of the positive and negative currents. The weight W is proportional to I1t1-I2t2 and is displayed at 15. Several variants of the switching, control and measurement circuits are described. The heat generation in the coil 4 may be kept constant or the extent of its variation reduced relative to that in known balances.