Patent GB-480708-A (GB)
Title: Improvements in or relating to electric remote metering arrangements
IPC: G08C19/16
Filed: 1936-08-27
Abstract: 480,708. Electric signalling systems. REYROLLE & CO., Ltd., A., LINSTOW, F. N., and RUTTER, F. G. Aug. 27, 1936, No. 23524. [Class 40 (i)] [Also in Group XL] In a remote-metering system, the meter readings are transmitted as pairs of impulses so that the ratio of the intervals between two impulses of a pair and two successive pairs is a measure of the reading, and at the receiver, each pair of impulses is converted into a single impulse of duration equal to the interval between the pair, the meter reading being indicated by the average value of the current derived from these impulses. Transmission may be effected by D.C. or audio-frequencies over a line, or by high frequencies by line or wireless. The line may be a power circuit and in the case of A.C., readings from a number of meters may be transmitted at different frequencies over the same line. In the simple system shown in Fig. 1, a contact B rotated by motor B1 sends pairs of impulses from battery C on passing a zero contact A2 and a meter-pointer contact A1. At the receiver, magnet D steps ratchet wheel E carrying a cam E1 having half as many projections as there are ratchet teeth so that contacts E2 close for the period between the impulses of a pair. The average current over E2 is indicated by a damped meter F1. If the receiver is one step out of phase, the meter indicates the complement of the correct reading and to avoid this, it is arranged that the interval between impulses of a pair, even at maximum readings, is less than the interval between successive pairs and the closure of contacts E2 for an excessive time operates relay G which energizes magnet D over its lower winding whereupon ratchet wheel takes one step. Alternating-current transmitters. Continuous oscillations are generated by the coupled lower grids of heptode J, Fig. 2, and a rotating arm H3 when moving over the zero and pointer members H2, H provides sufficient capacity coupling between the tuned anode and grid circuits J1, J2 to set up oscillations of a different frequency, impulses of the beat frequency being transmitted over line K1, K2. Alternatively, the rotating arm may vary the coupling between coils connected to the anode and grid circuits, Fig. 4 (not shown). In a modification, Fig. 3 (not shown) a simple high frequency oscillator valve is controlled as before by variations of coupling due to the rotating arm and the reduction of anode current when the valve is set in oscillation as the arm passes H2, H, Fig. 2, is used to control the bias on a separate low frequency oscillator whereby impulses of low frequency are transmitted to line. Photo-electric transmitters, Fig. 5. Light from a source O1 is reflected by a mirror 02 on the pointer to a rotating disc P having slots P2, P3 as shown so that as the light beam is moved radially outwards when the meter reading increases, the interval between the two pulses of light increases. In a modification, two parallel slots are provided, one on each side of a radial line, but in this case, the light beam is moved towards the centre when the meter reading is increased. Further, a rotating light beam may fall in turn on mirrors at the zero point and on the pointer. The output of photo-electric cell O modulates an audio-frequency oscillator. Receiver, Fig. 6. Impulses incoming over line K1, K2 are filtered at Q, amplified at Q1, rectified at Q2 and applied over condenser Q3 to the grids of a pair of discharge tubes, R, R of which only one at a time is conducting. Assuming R to be conducting, the next impulse causes a positive impulse on the grids (normally biassed negatively), R1 becomes conducting and due to fall of its anode potential and condenser R2 connecting the two anodes, the anode potential of R momentarily falls and R becomes nonconducting. Condenser R2 is made large to prevent the anode potential of R recovering before the grid re-assumes its normal negative bias on cessation of the impulse. The next impulse reverses the condition of R, R1 and so on. Thus R should be conducting during the interval between a pair of impulses, the average current being indicated on meter S connected directly in the anode circuit of R or controlled by a relay. Variations of anode current due to variations in supply voltage may be prevented by a barretter or neon tube stabilizer ; or a self-compensated meter of the ratiometer type may be used. To correct the receiver if it gets out of step, it is arranged that an auxiliary impulse is applied to the grid circuits. Tube R1 should be conducting for longer periods than non-conducting so that condenser T2 charges over T3, R1 for longer periods than the discharges over T3, R3. Normally, the charge on condenser T2 is high and the potential drop across tube T is low. If the receiver is out of step, condenser is uncharged, tube T flashes and a positive impulse is applied over condenser T4 to the grid circuits. The reading of the indicating meter is independent of the angular speed of the transmitter but the operation of the correcting device requires the transmitter speed to lie within limits. A modified correcting device, Fig. 7 (not shown), which is independent of transmitter speed utilizes the difference in potential of condensers charged over the respective tubes R, R1 to control the connection of an auxiliary impulse to the grid circuits.