Patent GB-510032-A (GB)
Title: Improvements in testing devices for electrical apparatus
Filed: 1938-04-13
Abstract: 510,032. Indicating faults; resistance measurements; valve voltmeters. GENERAL ELECTRIC CO., Ltd., and PALMER, S. T. April 13, 1938, No. 11271. [Class 37] A tester for a radio set or other apparatus comprises a sequence switch for successively applying various tests, whereby a lamp or other indicator is energized when a fault is found and remains energized until the end of the test cycle. A potentiometer resistance 4 is supplied from an auto transformer T3 through a barretter B1, transformer T1, rectifier Z1, and smoothing equipment 5, 6, 7, the voltage being further stabilized by gas discharge tubes S1, S2. The valve voltmeter comprises a D.C. amplifier formed by valves VI, V2, relays L, H, and an ammeter AM. The amplifier is supplied from an autotransformer T4, barretter B2, transformer T2. rectifier Z2 and smoothing circuit 8, 9, 10, 11, 12, and the supply is further stabilized by discharge tubes S3, S4, a portion of the stabilizing current being fed by the resistance 13 to the cathode of the valve VI for further stabilizing the normal anode current of the valve V2. The sequence switch has a driving magnet DM and contact banks DM1 ... DM4. The bank DM1 is connected to a number of neon lamps N1, N2, N3 &c. which are connected in series with resistances 15, 16, 17 &c. to a point on the potentiometer 4. These lamps have striking voltages about 30 volts above their extinguishing voltages, the voltage from the potentiometer 4 being between these values. The banks DM2, DM3, are connected by clips &c. to resistances T in the radio set under test. Comparison standard resistances TS are connected across the banks DM3, DM4. The resistances T, TS are connected in parallel with resistances R1, R2, so that if the test resistance differs from the standard the DC amplifier operates or releases relay L or relay H. A test cycle is commenced by throwing a switch AS, which charges a condenser 20 through a resistance 21 to a value sufficient to flash. through the tube S5. This operates relay NA momentarily, its contact NA1 operating a slow release relay NB, the contact NB1 of which energizes and releases the driving magnet DM so as to step the wipers DM1 ... DM4 one step forward. Wiper DM2 releases relay S which is operated when the switch is in normal position. Contact S1 maintains the operating circuit for relay NA so that the switch AS is now restored to the position shown. Contact S2 energizes a counter A showing the number of sets that have been tested. If the resistance T is too high, relay H is released and its contact H1 applies full potential to the lamp N1 causing this to light. If the resistance T is too low relay H remains operated but relay L is operated in addition, its contact L1 lighting the lamp N1 as before. Contacts d m open each time the driving magnet DM is energized and close as the wipers move on to the next step. During the period of opening the potentiometer R1, R2, restores the anode currents of the valves V1, V2, and consequently the relays H, L, to normal. At the conclusion of the test cycle the relay S operates and stops the switch from stepping further. If none of the lamps N1 &c. are lit, the resistances all have their correct value and the set is removed. If a lamp, e.g. N3, is lit the operator throws the switch ST, breaking the operating circuit of the relay NA, and steps the switch by a series of closing of the switch MS until the wipers connect the lamp N3. Contact H2 or L2 then indicates whether the resistance is too high or too low by lighting a lamp HR or LR. The switch is then stepped to normal and the next cycle commenced, the lamps N1 &c. being extinguished when the top contact of the switch AS opens. A relay and filament lamp may be substituted for each neon lamp, or drop indicators may be used. A relay chain or powerdriven switch may replace the step-by-step switch. The potentiometer test circuit may be replaced by a bridge connection.