Patent GB-462883-A (GB)
Title: Testing arrangements for electron discharge devices and methods of operating same
IPC: G01R31/24
Filed: 1936-07-17
Abstract: 462,883. Measuring currents and pressures. STANDARD TELEPHONES & CABLES, Ltd. July 17, 1936, No. 19889. Convention date, Aug. 16, 1935. [Class 37] The activity of an electron discharge device is determined by measuring the voltage drop in a resistance in the cathode circuit and finding from this measurement the time which elapses on reducing the normal cathode temperature for the cooling cathode to reach a certain degree of inactivity. In one arrangement which is applicable to a single valve or to any one of a number of valves 46, 47, the filament circuits are connected in series with jacks 54, 56 while the cathode circuits are connected to jacks 30, 30<1>, respectively. The test is made by inserting a plug 16 into one or other of the latter jacks according to the valve to be tested, whereby a meter relay 10 is connected across a resistance 28 in the cathode circuit. The meter relay is an ammeter with a high resistance 36 in series, and a variable resistance 37 enables a full-scale deflection of the pointer 35 to be obtained. The meter carries an adjustable contact 11 which is set to any desired value, and is in the form of a small magnet which attracts an iron rider on the pointer 35, to give a good contact. A plug 57 is then inserted in the jack 54 or 56 and a key 12 is depressed to interrupt, or alternatively, if a resistance is shunted across the key, to reduce, the filament current through the valve. The key 12 also completes the circuit of a clock or other time measuring instrument 13 and at the same time the key may connect with the series circuit a resistance 58 equal to that of the filament which has been cut out, thereby leaving the filament circuits of the remaining valves unaffected. As the filament of the valve under test cools, the pointer 35 returns until it engages the contact 11, which completes the circuit of a relay 15. This relay through its contact 43 completes a hold-in circuit for the relay, interrupts the circuit of the clock 13 through a contact 42 and re-energizes the circuit of the filament of the valve by short-circuiting the appropriate contact 38 of the key 12 through contact 41. The clock 13 then indicates the time required for the current in the cathode circuit to fall by a predetermined amount and this is proportional to the emissivity of the valve. In a modification, in which the valves under test are again connected in series, jacks such as 30, 301 are provided across the resistances 28 of each valve circuit, and plugs similar to plug 16 are provided each connected to a meter relay such as 10 and a relay such as 15. Only one jack is provided in the filament circuit and when the plug is inserted in this, the cathodes of all the valves are cooled but due to the difference in the emissivities of the valves, the pointers 35 of the meter relays return at different rates, that for the valve having the worst emissivity engaging its contact 11 first and energizing its relay 15. This closes the circuit of a relay which interrupts the circuit of the clock 13 which was closed as before by a key 12. The relay also operates a lamp or other alarm, indicating which valve is faulty, and re-energizes the filament circuit of the valve. In a modified form of this arrangement, the clock is replaced by a condenser-resistance circuit and a number of " trigger " valves, one for each valve to be tested. The condenser is normally connected to a battery but when the key 12 is operated, this connection is broken and the condenser discharges slowly. When the meter pointer 35 engages its contact 11, a relay is energized which connects the condenser to one of the trigger valves and this valve operates if the voltage of the condenser is sufficiently high, i.e. if the time which has elapsed since the filament circuits were interrupted by the key 12 is less than a predetermined amount. The apparatus is applicable to testing valves connected in series or parallel more particularly those used in a continuously operating communicating system; the system is not interrupted by the test as the current in the cathode circuit is not allowed to fall below a value which enables the system to continue in operation.