GB1112521A - Anodization control circuits - Google Patents

Abstract

1,112,521. Manufacturing resistors. WESTERN ELECTRIC CO. Inc. 26 Aug., 1965 [1 Sept., 1964], No. 36622/65. Heading H1S. Apparatus for adjusting the resistance of a resistive device by anodizing, comprises an electrolytic anodizing cell, means for testing the resistance of a device within the cell, means for alternately inhibiting the supply of current to the cell so that a resistance test may be effected and permitting current supply to anodize the device, and means responsive to the attainment by the device of a desired resistance to terminate the anodizing. The device to be anodized is an etched thin film resistor 110 of tantalum on a glass substrate 111, the contacts 112 being successive layers of nickel-chromium alloy, copper and gold. The resistor 110 is incorporated as the anode of an electrolytic cell 114 and is also connected in a common arm of two Wheatstone bridges 147, 148 which provide resistance testing means, bridge 147 balancing when resistance 110 equals the lowest acceptable value, and bridge 148 balancing when resistor 110 equals the highest acceptable value. An A.C. source 161, connected to the cathode through a diode 164 supplies anodizing current to the cell during one half cycle and testing current to the bridges during the other half cycle, the value of resistance 110 increasing until an acceptable value is provided at which stage anodization terminates. A mercury wetted relay 18 is connected to the A.C. source 161 so that during anodization half cycles it shorts the outputs of the bridges, and during testing half cycles it removes the shorts so enabling sensing of these outputs by detectors 168, 173. The detectors 168, 173, connected across the outputs of the bridges 147, 148, each comprise an A.C. or D.C. amplifier and a relay, relay 171 controlling contacts 167 and 172, and relay 176 controlling contacts 177 and 178. An indicating circuit includes lamps 182, 183, 184, contacts 172, 177 and 178 and source 161. In a modification of the circuit of Fig. 6 (Fig. 3) only one Wheatstone bridge is employed and a diode is connected across its output to short it during anodization half cycles. In a different circuit arrangement (Fig. 1), an adjustable constant voltage D.C. source (33) supplies anodizing current to the cell through a normally closed contact (34) and a constant voltage, or current, D.C. source (22) supplies testing current to the single Wheatstone bridge, a normally closed contact (36) being connected across the bridge output to short it so that testing current does not reach detector (28). A timing circuit (37) alternately opens and closes contacts (34, 36) to provide several interrupted periods of anodization and testing.