Patent GB-288685-A (GB)
Title: Improved method of electric testing and measuring and circuit arrangements therefor
IPC: H04M1/24
Filed: 1927-01-06
Abstract: 288,685. Siemens Bros. & Co., Ltd., and Grinsted, W. H. Jan. 6, 1927. Automatic exchange systems.-The duration of electric impulses or parts thereof is measured by connecting a source of current to an electromagnetic quantity meter for the time during which the impulses endure. The invention may also be used to measure the operating- lag or release-lag of a relay. The Figure shows circuit-arrangements for measurements of speed, relative lengths of " make " and " break," &c. of a dial impulse-transmitter. The meter M is similar to the Grassot fluxmeter and consists of a suspended coil mounted on a copper former in the field of a permanent magnet. There being no restoring spring, return to the normal position is effected by passing a reversed current through the meter either by a reversing key or by the discharge of a condenser which is charged during the operation of the meter. The meter may have two scales of showing, respectively, time and number of impulses per second. In order to obtain a full scale reading whether one or mine impulses are being measured, two alternate series resistances X, 9X are employed. To calibrate the meter before use, key 6 is thrown to the left completing a circuit from a special battery AB over resistance VR and over parallel branches M, 9X, and MR, X back to battery. Resistance VR is adjusted until voltmeter P gives a standard reading. The meter is restored after any deflection by throwing key 6 to the right thus reversing the connections to battery AB. To perform a series of tests, the dial is connected to terminals T and key 1 operated, energizing relays A, V, D. To test the total number of impulses transmitted, key 2 is thrown to the left and the digit O dialled. Impulses are repeated at contact a3 to the operating magnet DM of a step-by-step switch A - - E and at the end of the digit the position of wiper C indicates on a lamp bank L1 - - L11 the number of impulses received. At the end of the test, key 6 is thrown to the right, releasing relays A, V, and restoring switch A - - E. To measure the time occupied by nine impulses, key 2 is thrown to the right so that meter M is connected to battery AB over resistance 9X, key 6, resistance VR, wiper A and contact d4. The digit O is dialled as before but wiper A only engages with the continuous segment of its bank from the first release of relay A to the tenth break, and the meter M thus indicates the time of nine impulses. The measurement of the total ' make ' and total break ' periods of nine impulses are similarly effected in the two positions of key 3, the circuits between meter M and bank A containing, respectively, a front and back contact of relay A. The duration of any particular impulse is determined by means of key 4 and one of the keys K1 - - K9 connected to the bank of wiper B, and the measurement of the ' make ' and ' break ' intervals of particular impulses are similarly effected by key 5 and keys K1 - - K9. Keys 4 and 5 operate relay R which replaces resistance 9X in series with the meter by resistance X. Since the switch A - - E steps on the energization of its magnet DM and therefore normally on the release of relay A, measurements of ' break ' periods might be incorrect owing to the movement of the switch wriper during a measuring period. To avoid this. circuits are completed in the right positions of keys 3 and 5 whereby an initial step is given to magnet DM over contact j2 and wiper D whilst successive operations of the magnet take place over contacts j2, d2, and front contacts a3. Instead of using a constant source of current AB. measurements may be made by using as a source a charged condenser, the rate of discharge at any time being dependent upon the time from the commencement of the discharge, the meter being graduated logarithmically. Such an arrangement may be used to measure the operating-lag or release-lag of a relay. For example, to measure the former, a standard relay of negligible or known lag is arranged when unoperated to charge a condenser and when operated to connect the condenser to the meter, the relay under test being connected in parallel with the standard relay and having its back contact in series with the meter.