Patent GB-835095-A (GB)
Title: Remote metering by means of impulse series
IPC: G08C19/22
Filed: 1957-10-17
Abstract: 835,095. Telemetering. ALLMANNA SVENSKA ELEKTRISKA A.B. Oct. 17, 1957 [Oct. 19, 1956], No. 32422/57. Class 40 (1). [Also in Groups XXXVI and XL (c)] The value of a quantity is measured at a remote position by generating a train of electrical impulses such that the periodic time of each impulse and succeeding space is proportional to the quantity, obtaining at the receiver another quantity proportional to the periodic time, storing this quantity until a further quantity proportional to the next period is obtained, and then passing the earlier quantity to an indicator. Transmitter.-In Fig. 1 the capacitor 4 charges from a constant-current source 5 through resistor 10, thus applying a negative voltage to the base of transistor 9, allowing it to conduct; the base of the transistor 8 is thereby earthed and it is held cut off. When the voltage across 4 and 10 equals that of the source 7 (proportional to the quantity to be measured) the diode 6 conducts and the condenser ceases to charge. The base of transistor 9 now falls to earth potential, cutting it off and opening transistor 8 to receive the discharge current of the capacitor. The base of transistor 9 now goes positive (limited by diode 12) so that transistor 8 is made fully conducting by a multivibrator action. When the condenser is fully discharged the voltage across 10 disappears, transistor 9 conducts somewhat and transistor 8 is cut off. The condenser then starts to charge again to initiate a fresh cycle. The output is taken from the collector of transistor 8 in the form of short pulses whose periodic time is proportional to the voltage at 7. These pulses are applied to the further multivibrator 14, 15 to generate square waves of the same period, thereby energizing the relay 20 to send corresponding pulses along the line 2 to the receiver. The alternative transmitter of Fig. 3 contains two capacitors 40, 46 charged alternately from a constant current source 41 to the potential 44 representing the quantity to be measured. With the relay contacts as shown the capacitor 46 is charged through the base of the transistor 52, which therefore conducts and holds its collector at earth potential. Capacitor 40 is short-circuited and transistor 53 is cut-off since its base is at earth potential, and therefore its collector is at the negative line voltage. When capacitor 46 is charged to the potential of 44 the diode 48 conducts and the charging current ceases. The base of 52 then drops to earth, the transistor is cut off and its collector falls to negative line voltage. A negative pulse is thus sent via 58 to open up the transistor 51 and operate the relay 49; contact 49b maintains the negative potential on the base after the pulse has ceased. The change-over of contact 49a starts the charging of capacitor 40, opens up transistor 53 and thus (via 60) further cuts off 52, sending a further pulse to open up 51. The base of the latter is then held positive by the discharge current of 46. When capacitor 40 reaches the potential of 44 the reverse cycle occurs in the same way and the relay 49 is deenergized. As before, pulses are sent down the transmission line by operation of contacts 49c. Receiver.-The pulses operate relay 36, and contacts 36a energize two further relays 22, 23, the latter being slow to make and break. With the contacts as shown (i.e. space condition) capacitor 25 is charged via resistor 28 and capacitor 24 is short-circuited through resistor 29, the reverse conditions obtaining during a "mark." The source 26 supplies a constant current so that the voltages across the capacitors become proportional to the space and mark durations respectively. At the end of a mark the voltage across 24 is transferred to a storage capacitor 30 via contacts 22a which close before the short-circuiting contacts 23a. Similarly at the end of a space capacitor 25 transfers its charge to 31 via 22b before it is short-circuited by 23b. The capacitors 30, 31 are smaller than 24, 25 so that the voltages do not change appreciably during the transfer. The electrometer amplifier 34 has a high input impedance so that its input is proportional to the average of the voltages across 30 and 31, i.e. to the sum of the mark and space intervals. The large resistors 32, 33 prevent the capacitors 30 and 31 from sharing their charges with each other. Modifications.-The sources 5 and 26 need not be of the constant current type as long as their time constants are equal, as the non- linearities in the transmitter and receiver will then cancel out. The input 7 can be cyclically switched to a number of channels, with corresponding selectors at the receiver actuated by the pulses themselves. The receiver may contain only one charging circuit and one capacitor which is charged during mark and space, the voltage being transferred to the two storage capacitors at the end of the mark and space respectively; the capacitor is rapidly discharged at the end of the space.