A load placed on the support 11 is balanced by a pulsed current in coil 13 whose duty factor is controlled by gating pulses applied to electronic switch 22. The control is effected according to the output of position sensor 14 through a digital processing unit 5 and the resulting measurement is displayed on unit 6.
Relatively cheap standard 16-bit digital circuits are used to generate the gating pulses by counting clock pulses. The discrimination available is limited to steps of one clock pulse between successive gating pulses and the clock frequency is limited by the 16-bit capacity of the digital circuits. To simulate greater discrimination and achieve greater accuracy of weighing successive groups of gating pulses are made to include an increasing proportion of pulses differing by one step in width from the other pulses. Thus by averaging over each group it is possible to interpolate between successive gating pulse widths separated from each other by one clock pulse.