Patent GB-1279420-A (GB)
Title: Data communication system for automatic remote meter reading system
IPC: H04M11/00
Filed: 1969-08-14
Abstract: 1279420 Remote reading apparatus McGRAW EDISON CO 14 Aug 1969 [21 Aug 1968] 40693/69 Headings G4D D1D1 D6Y and D6L Apparatus for the remote reading of for example meters includes at each meter an encoder converting to digital form the meter reading, the level of a parameter e.g. frequency of a transmitting circuit being varied by the digital signals this variable level being transmitted together with a reference level to a receiving station where it is de-coded. When a meter reading is to be taken a line selector (4) Fig. 1 (not shown) connects lines (19, 20) to a transponder exciter (5) which is energized to provide a signal of one polarity across conductors 19, 20 Fig. 2 to allow sufficient charge to accumulate on a capacitor C8 for a neon N to break down causing photo-cell PC1 to go to its low impedance state to couple conductors 19 and 69. After a delay determined by circuit 77 during which delay Colpitts oscillator 61 is energized by the voltage across terminal 63, 64 of diode bridge 60 to transmit a reference frequency, lamp 27 is illuminated so that selected ones of photo-cells 50, 51, 52, 53 dependent on the setting of a meter coupled disc 22 go to their low impedance state. Capacitors C1-C4 in parallel with capacitor C5 of the oscillator and in series with photo-cells 50-53 vary the frequency of the oscillator output in accordance with the setting of disc 22 to transmit a frequency α. The polarity of the transponder exciter output is then reversed to illuminate lamp 26 and a frequency # representing the setting of disc 21 is transmitted. The frequency signals are fed via a distortion equalizer, an automatic gain control circuit Fig. 9 (not shown) and band pass filters to a frequency to digital converter, Figs. 10a, 10b. A phase locked loop 142 feeds a signal 143 of the same phase and frequency as the input to the converter to a period difference counter 147 which also receives a reference frequency from generator 149, clockpulses on conductor 152 being counted to give an indication of the difference between the signals on leads 143, 148. An up/down signal on conductor 154 indicates which signal is the larger. The counter 147 forms a signal I lasting ten cycles of the signal from generator 149 and a signal E lasting ten cycles of the signal on conductor 143, clockpulses being accumulated via a divide by ten circuit 155 additively when E.I = 1 and subtractively when E.I = 1 the pulses from the divider are fed to a reference counter, α counter and # counter. The frequency of the signal from generator 149 is varied in accordance with the count in reference counter 160 the binary coded output from which controls via reed relays (RS1-RS9) Fig. 1 (not shown) the switching in of binary coded inductances (L3-L11) to balance the frequency of the generator 149 and reference signal. Capacitances C16-C19 controlled via relays (RS10-RS13) by the α and # counters balance the α and # frequencies with the signal from the generator so that the α and # counters give a digital indication of the transmitted frequencies relative to the reference frequency. Three samples of the reference frequency lasting for ten cycles are first digitized so that the generator 149 gives successively closer approximations to it a fourth sample of a hundred cycles then being digitized to give a better approximation. This is repeated for each of the measured frequencies α, #. The pulses on conductor 156 are fed to the α and # counters 161, 162 via a count dependent divider 216 since the relationship between the number of output pulses on conductor 156 and the number of capacitive changes in the generator 149 is non-linear.