Patent GB-413726-A (GB)
Title: Improved method of testing telegraph apparatus and systems
IPC: H04L12/26
Filed: 1933-01-19
Abstract: 413,726. Testing - apparatus for telegraphy. JOLLEY, E. H., 19, Barn Rise, Wembley Park, Middlesex. Jan. 19, 1933, No. 1781. [Class 40 (iii).] Distortion of five - unit start-stop signals, the tolerance of a receiver, and distortion due to the transit time of relay armatures are measured by means of a neon-tube stroboscope and of a test transmitter which permits the lengths of two of the signal elements to be varied. Test connections. By means of switches 21, K6, it is possible to connect (i) the testing- transmitter TT to the teleprinter TP, for finding the latter's tolerance for distortion of received signals ; (ii) the testing-transmitter to the output terminals 26, 27, for sending test signals to line ; (iii) the teleprinter TP to the output terminals 26, 27, which are then connected to terminals 28, 29 either directly or through a line, for testing the distortion due to the transmitter or to the transmitter and line. Testing-transmitter. The test distributer, Fig. 1, in which the brush 8 rotates clockwise, comprises five combination segments 11-15 equal in length to the stop segment 16, together with a start segment 10 which is half as long again as the others but is partly shielded from the brush 8 by a movable plate 17 which is connected to the stop segment 16 but insulated from the start segment 10, so that the effective lengths of the start and stop impulses can be varied by movement of the plate. A five-unit test signal is set up on the keys K1-K5; for testing the effect of bias, the battery can be reversed by means of key K8 ; and for stopping, starting without emission of signals, and starting with emission of signals a key K7 is provided. A cam may be provided for sending at will alternate signal groups of which one consists of marking impulses while the other consists of spacing impulses except for the stop signal. Stroboscopic receiver. Signals are received at terminals 28, 29, Fig. 1, and operate a neon lamp which is connected to terminals 30, 31, and is momentarily ignited each time that armature 35 is reversed by a change of signal polarity. The lamp may be either a small neon lamp rotating with a stroboscopio disc-shaped mask and visible through a radial slot therein, or a large neon lamp situated under the stroboscopic disc and visible through the rotating slot. Fig. 2, in which the movement is anticlockwise, shows the appearance when a start signal - is followed by the combination - + - + - and the stop signal +. The dotted lines show the positions of the flashes given by perfect signals, while the full lines correspond to signals in which the + impulses start too late and end too early. The scale may be rotatably adjustable by hand, or may rotate continuously if the stroboscope is not exactly synchronized. For testing the transit-time and shutter of the receiving relay, the system shown in Fig. 3 is adopted. The relay armature 51, when at rest on either contact, shortcircuits the lamp 56 through the transformerprimary 57. When it leaves one contact, however, a momentary impulse is added by the transformer to the voltage of the battery 55 and aids the striking of the lamp. When the armature reaches the other contact this action is reversed and the lamp goes out. Hence the breadth of the stroboscopic line indicates the duration of the transit of the armature, and a plurality of lines indicates chattering.