. The Bell System technical journal . gh the coupling circuit to the associated C tube. Each multivibrator stage consisting of the A and B tubes with othercircuit elements is mounted on a plug-in turret which may easily bechanged in case of trouble. BRIGHTNESS CONTROL CIRCUIT When pulsing a relay the armature remains on the operated and re-leased positions for a relatively long time interval. If the intensity ofthe scope beam is allowed to remain constant the spots at the ends of thetraces are bright enough to fog the entire scope face. This makes itdifficult to see the relatively weak lines t
. The Bell System technical journal . gh the coupling circuit to the associated C tube. Each multivibrator stage consisting of the A and B tubes with othercircuit elements is mounted on a plug-in turret which may easily bechanged in case of trouble. BRIGHTNESS CONTROL CIRCUIT When pulsing a relay the armature remains on the operated and re-leased positions for a relatively long time interval. If the intensity ofthe scope beam is allowed to remain constant the spots at the ends of thetraces are bright enough to fog the entire scope face. This makes itdifficult to see the relatively weak lines that are caused by the motionof the armature. Therefore a control circuit is pro^ided to brightenthe scope trace only when the relay armature is in motion. The circuitshown on Fig. 8 provides the voltage required to intensify the cathodebeam of the scope. This voltage is obtained by differentiating the outputvoltage of the electrostatic gauge. As the latter is proportional to the 934 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1954 +165 V. Fig. 6 — Schematic circuit of two switching stages showing modulator tubes(C) and their associated multivibrator tubes (A and B). ELECTRONIC RELAY TESTER 935 armature position, the clifferentiatod voltage is proportional to thearmature velocity. After amplification the voltage from the gauge isapplied to a tube with a transformer in the plate circuit. The voltageacross the secondary coil of the transformer is the differentiated voltage,proportional to the armature velocity. It is applied to a germanium diodebridge, which may be connected as a half-wave or full-wave rectifier bythe selector switch. The rectified voltage is amplified and clipped andthen applied to the Z axis terminals of the scope. The scope trace isbrightened during operate, during release, or during both in accordancewith the setting of the bridge selector switch. GAUGING A RELAY The rela} is plugged into a holding fixture with a jack for the coil andcontact terminals. The jack
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