Patent GB-698983-A (GB)
Title: Improvements in impulse telemetering systems
IPC: G08C19/22
Filed: 1951-06-29
Abstract: 698,983. Electro telemetering systems. LEEDS & NORTHRUP CO. June 29, 1951 [July 1, 1950], No. 15503/51. Class 40 (i). In a telemetering system wherein impulses of duration proportional to the magnitude of a variable are transmitted, the receiver includes a relay energized by each pulse and serving to charge a capacitor to a voltage proportional to the pulse duration, the voltage being measured by a meter which is disabled while the capacitor is being charged. Transmitter, Fig. 1. An insulating drum 10, driven at constant speed by a motor 11, has a conducting surface 12 so shaped that the fraction of each revolution during which it engages a contact 13 depends upon the position of the contact axially of the drum. The contact is adjusted axially in accordance with the magnitude to be transmitted e.g. mechanically by a meter 15. A known arrangement 17 produces pulses which are transmitted over lines 18a, 18b, corresponding in length to the axial position of the contact 13, i.e. to the magnitude to be transmitted. The pulse recurrence frequency is constant in this case, and the duration of each pulse and the following space are complementary. Transmitter, Fig. 2. In this arrangement the spaces between the pulses are of constant duration. The magnitude to be transmitted, in the form of a voltage E, charges a condenser 51 over a resistor 50 until a discharge tube 53, series connected with a relay 40 across the condenser, fires, whereupon the discharge current energizes the relay to break the charging circuit at contact 40c. Falling off of the relay is delayed by a rectifier shunt 54, after which the charging circuit is remade at contacts 40c and the cycle is repeated. Pulses are sent to line through the device 17 by a battery 55 while the relay 40 is de-energized i.e. during the charging time of the condenser 51, and as the charging time varies inversely as the magnitude E, the durations of the transmitted pulses vary inversely with E. The spaces between pulses correspond to the discharge time of the condenser 51 which is substantially constant. A biasing battery 52 is provided if E is less than the break down voltage of the tube 53. Transmitter, Fig. 4. The drum 10 of Fig. 1 is replaced by a cone having a conducting surface 56 and an insulating portion 57 having substantially parallel sides. The cone is driven frictionally by a contact disc 59 rotated by a constant speed motor 58, the disc 59 also being moved axially, i.e. parallel to the slant edge of the cone by the meter 15 to vary the rotational speed of the cone and also to vary the time of contact of disc 59 with the conducting cone portion 56 per cycle. The contact 13 moves axially with the disc 59 and recurrent pulses are produced in the device 17 corresponding in duration to the indication of meter 18. Transmitter, Fig. 5. Here the magnitude indicated by the meter 15 is transmitted only when the magnitude changes. The meter movement actuates the contact 13 as in Fig. 1, and also mechanically actuates the slider of a potentiometer 63. A change in the meter reading thereby produces a pulse through a relay 62 which closes immediately to energize the motor 11a which starts to drive the drum 10 at constant speed. Immediately the contact 13 engages the drumconducting portion 12 a relay 61 is energized and sends a pulse to line over contact 61b and maintains the motor circuit at contacts 61a. The relay 62 is delayed in its release by a dashpot, at least for a time, to ensure locking of the motor circuit by relay 61, in which case only one line impulse is sent, the motor circuit being broken as relay 61 relapses as contact 13 engages the insulating portion of the drum 10. The release of relay 62 may, however, be delayed for a longer period to allow several pulses to be transmitted. Receiver, Fig. 1. Each line pulse operates relays 20, 21 at the receiver. As contact 21b pulls up, it first engages a contact 21d to short circuit and discharge the receiving condenser 30. On further movement of contact 21 b the discharge circuit is broken at contact 21e and the receiving condenser is charged over a resistor R from a battery 35 for the duration of the line pulse. At the end of the line pulse contact 21b relapses to connect the receiving condenser 30 across the storage condenser 31. If the magnitude being transmitted has not changed since the preceding line pulse the voltage to which the receiving condenser 30 has been charged will be equal to that across the storage condenser, and the connection together of these condensers as the line impulse ends has no effect on the voltage across the storage condenser. If, however, the transmitted magnitude has changed, connection of the two condensers together at the end of the line pulse produces a corresponding change in the voltage across the storage condenser which thus assumes a value which always corresponds to the magnitude. The relay 20 is delayed both in its actuation and release and serves merely to ensure that the discharge circuit for the receiving condenser 30 is completed as above described as the relay 21 pulls up, but not as it releases. The voltage across the storage condenser may be measured in any known manner. For example, it may be compared in an automatically balanced potentiometer device 32-34 with a potential derived from the arm of a potentiometer 32. The two potentials are applied successively to the input of a detector 33 by a vibrating contact 33a, any difference in the two potentials resulting in a detector output which drives a motor 34 to adjust the arm of the potentiometer 32 until the balance is restored. The circuit to the motor 34 is broken by the relay 21 to disable the meter during reception of a line pulse. Since the measuring device 32-34 responds only to changes in the magnitude being transmitted, it is suitable for use with the transmitter of Fig. 5. In a modification, Fig. 3 (not shown), the line relay 20 is dispensed with, the remaining line relay 21 being provided with an additional contact delayed by a dashpot, for effecting the circuit functions of relay 20 in Fig. 1.