Improvements in and relating to electrical measuring, indicating or recording apparatus

摘要

878,670. Electric tests. CAMBRIDGE INSTRUMENT CO. Ltd., and BECK, H. V. Oct. 23, 1957 [July 23, 1956], No. 22714/56. Class 37. In electrical measuring apparatus, a movable element is displaced to an extent dependent upon the value of an input current; a control current and a rate current, dependent respectively upon the extent and the rate of displacement of the element, being derived which cause a corresponding force to oppose the motion of the element; whereby the element rapidly assumes in dead beat manner a position indicative of the input current value; there being substantially no mechanical restoring force applied to the element. An input current is fed by way of amplifiers 11, 12 to a moving-coil galvanometer 13 having negligible mechanical restoring force, the moving coil carrying a vane 14 which forms, with vanes 15 and 16, a differential capacitor connected in a bridge circuit incorporating the primary winding 17a of a high-frequency transformer 17; high-frequency oscillations being applied across the bridge from a generator 18. The secondary winding 17b of the transformer 17 feeds a phase-sensitive rectifier 21, to which the output of generator 18 is applied as a reference; the output from rectifier 21 is fed to amplifier 12 and constitutes the control current acting in opposition to the input current. The rate current is derived by feeding the output of rectifier 21 to a differentiating circuit 22, the output of which is applied, through amplifier 24, to amplifier 12 where it is combined with the input and control currents. In modifications, the differential capacitor 14, 15, 16 may be adjusted by varying the separation instead of the overlap of the plates; the differential capacitor may be replaced by a device which modifies light incident upon one or more photo-electric cells, or by a movable coil adjacent two stationary coils.