Patent GB-772869-A (GB)
Title: Improvements in or relating to systems for tele-metering
IPC: H04B1/66
Filed: 1953-12-23
Abstract: 772,869. Electric selective signalling. SWENSSON, S. O., and NORDEN, K. E. Dec. 23, 1953 [Dec. 23, 1952], No. 35795/53. Class 40 (1). In a telemetering system for transmitting values of a plurality of continuously varying variables, a sampled value of each variable, together with its first and second differentials are periodically recorded in memory blocks where these values are converted into corresponding electrical quantities, e.g. voltage, current, frequency. These values are then transmitted, in code, to the receiver where the highest order differential is used to indicate the variable by repeated integration. Initially the actual value of the variable, and both its first and second derivatives are transmitted for initially setting up the receiver indication. Subsequently, the actual value and the first derivative are transmitted only at relatively long intervals for checking and correcting purposes. Synchronous distributers at transmitter and receiver are used to transmit the data associated with different variables, sequentially. Transmitter, Fig. 4. Amplitudemodulated pulses representing a plurality of variables are connected in time-division-multiplex fashion to lines x, y, each signal on line x appearing simultaneously with a signal on line y so that each such signal pair may be represented by a point in a two-dimensional co-ordinate system. The signal pulses are fed to respective memory blocks M1, M2 . . . &c., one for each variable. Each block comprises a gate G which passes the input voltage pulse only if it lies within a predetermined amplitude range, a locking gate K which passes the input pulse from line x only if a corresponding pulse is being passed from line y to M2, and a device T which translates the input pulse into a static voltage which is stored in a memory M. Preferably the elements T, M include a potentiometer, the slider of which is set by a servomotor in accordance with the amplitude of the input pulse. Any difference between the voltage of an incoming pulse and the setting of the potentiometer (the stored voltage) is fed to a derivative device Td<SP>1</SP> and thence to a second memory M<SP>1</SP>. The elements Td<SP>1</SP>, M<SP>1</SP> function similarly to T, M to set a potentiometer according to the successive differences, i.e. the first differential of the variable. In a similar manner the second and third differentials are recorded by elements Td<SP>11</SP>, M<SP>11</SP> and Td<SP>111</SP>, M<SP>111</SP>, respectively. The values stored in the memories M, M<SP>1</SP>, M<SP>11</SP> are fed by a sequence switch DM . . . DM<SP>11</SP> to corresponding coders CM . . . CM<SP>11</SP>, e.g. binary coders, and a coded signal corresponding to the value of the variable, its first differential or its second differential is transmitted via a selector switch OI to line L. Normally it is only necessary to transmit the second differential value of each variable, the selector switch OI being operated to transmit the values of the variables and their first differentials at relatively long intervals for checking purposes. A unit H corrects the values of the second differential derived from the memory M<SP>11</SP>-by subtracting the third differential therefrom-before coding. The pass range of the gate G is controlled by a feedback signal from the memory M so that the recorded voltage is always equal to the midpoint of the range. Receiver, Fig. 5. The transmitted signals are fed by a selector switch OII, operated synchronously with OI, Fig. 4, to corresponding decoders DCM . . . DCM<SP>11</SP>, and thence via a sequence switch FDM . . . FDM<SP>11</SP> operated synchronously with DM, Fig. 4, to integrating blocks Ig1, Ig2 . . . corresponding to the variables in question. The blocks Ig1, &c. are analogous to the transmitter memory blocks M1, M2, &c. and consist of servo-controlled potentiometers. Thus the second differential of a variable fed from decoder DCM<SP>11</SP> sets over FDM<SP>11</SP> the potentiometer of a function generator U2 accordingly. The voltage " picked off " by this potentiometer is fed to a similar generator U1, the servomotor of which is so controlled that it moves its potentiometer slider at a rate proportional to the input from U2, so that the U1 slider is set according to the integral of its input from U2, i.e. according to the first differential of the variable. In a similar manner the potentiometer in U0 is set from U1 according to the value of the variable. Successive values of the second differential of the variable are also compared at U2 and should they differ by a predetermined amount, a device RII is actuated which, in co-operation with a device RI, Fig. 4, prevents stepping of the sequence switches DM . . ., FDM . . . and moves selector switches OI, OII so that the first differential of the variable in question is transmitted via DCM<SP>1</SP>, FDM<SP>1</SP> and compared at K1 with the value of the first differential recorded at U1. Any difference will set the potentiometer in U1 according to the transmitted value, and should the difference exceed a predetermined value, the devices RII, RI, are again actuated to move the selectors OI, OII so that the value of the variable is transmitted and compared at K0 with the potentiometer setting in U0 for similarly correcting the setting thereof. Should the comparator K0 indicate a large difference, the devices RII, RI are again actuated to cause continuous transmission of the actual value of the variable until the difference is removed. Initially the absolute value and both first and second differentials of each variable are transmitted to set up the potentiometers in U0, U1, U2. Modifications. The arrangement of Fig. 4 in which gates K are provided for passing signals only if the two co-ordinate variables x, y are both " present " simultaneously, may be extended to three co-ordinate signals. The memory blocks M1, M2, &c., Fig. 4, may convert the incoming signals into corresponding variations of frequency of local oscillators, the memories in this case being magnetic.