Patent GB-771467-A (GB)
Abstract: 771,467. Electric signalling systems. ANTAR PETROLES DE L'ATLANTIQUE, [formerly RAFFINERIES FRANCAISES DE PETROLE DE L'ATLANTIQUE], REYMONENQ, G., and OUVRARD, P. Jan. 25, 1955 [May 4, 1954], No. 2242/55. Class 40 (1). In a system for transmitting the indications of a measuring apparatus, the measurement range controlled by the apparatus is divided into a predetermined number of divisions and the quantities measured are transmitted in the form of periodical impulse trains each comprising at least three impulses, namely a timing impulse, a first measurement impulse, the phase of which is shifted with respect to that of said timing impulse by an amount corresponding to the relative posi - tion of the division with which the measured quantity is associated at that instant, and a second measurement impulse, the phase of which is shifted with respectto that of said timing impulse by an amount corresponding to the exact position of thequantity measured within said division. As shown, the measurement to be transmitted is the level of a liquid in a tank 5, which is detected by a float 6 and indicated by a dial 1 co-operating with an index 2. The movement of the dial 1 and shaft 3 is transmitted to a shaft 12 through gearing 10, 11, such that when the dial rotates from O to M, the shaft 12 effects a number of revolutions equal to the number of divisions on the dial, as shown, twenty-five. The shaft 12 carries a gear 13 and a disc 14 having a driving pin 15, the gear 13 driving a hollow toothed drum 16 which makes twenty-five revolutions as the dial 1 rotates from O to M. For each revolution of the shaft 12, the pin 15 drives a notched disc 17 through one step, which through a pinion 18 drives a hollow toothed drum 19 so that it rotates by an angle equal to the angular extent of the scale of the dial 1 each time the dial 1 is rotated from O to M. The drum 19 can assume twenty-six positions corresponding to the twenty-six graduations on the scale 1 and its position identifies the graduation immediately preceding the index 2, the position of the drum 16 precisely indicating the angle between that graduation and the index 2. Magnetic scanning heads 20, 21 are carried by drums 16, 10, respectively, and co-operate with members 23, 24 on a shaft 26 driven at constant speed by a motor 27 to generate the measurement impulses 30, 31, Fig. 3, and determine their phase with respect to timing impulses 29 generated by a fixed magnetic head 22 co-operating with rotary member 25 on the shaft 26. A further fixed magnetic head 62 generates a calibration impulse 63. For the remote transmission of the measurements, a high-frequency oscillator, Fig. 4 (not shown), is modulated by the impulses, the high-frequency emission being blocked each time the negative timing pulses 29 occur, and the output is applied to a transmission line, e.g. the power mains. At the receiver, Fig. 5 (not shown), means are provided for successively receiving transmissions from a number of remote stations each using a different radio frequency, the input being applied to a frequency changer having an oscillator tunable in steps to provide an output at a fixed medium frequency which is applied to a double detector stage to provide one output corresponding to the impulses 29, 30, 31, 63, and a second output corresponding to the same impulses reversed in polarity. These outputs-are separately amplified, one amplifier being biased so that only the timing impulse 29 is passed and is applied to control the time base of a cathode-ray tube, all the impulses being passed by the other amplifier and applied to the cathode-ray tube to produce the display shown in Fig. 6. Using two suitable scales 61, 61<SP>1</SP>, the division of the measurement range is read opposite 31<SP>111</SP> and the accurate measurement within that division is read opposite 30<SP>111</SP>. When the timing pulse 29<SP>111</SP> is brought into registration with the zero of the scales the position of the calibration pulse 63<SP>111</SP> provides a check on the readings.