Patent GB-657394-A (GB)
Title: Improvements in electrical remote indicating systems
IPC: G08C19/00
Filed: 1949-02-22
Abstract: 657,394. Electric control systems. GENERAL ELECTRIC CO., Ltd., FIELD, R. W. G., and POPE, B. W. Feb. 22, 1949, No. 4799. [Class 40 (i)] [Also in Group XIX] The readings of rotary meters are normally transmitted to a central station at the end of recurrent predetermined periods, and provision is made for transmitting an approximate indication of the trend of any particular meter, at the end of a sub-multiple of the predetermined period, only if an appreciable change has taken place in the rate of revolution of the meter. As shown, each meter impulses an associated relay M, e.g. once per revolution, these impulses being passed by contact M1 to a " full time " binary counting relay chain AM-MF, similar to that described in Specification 644,041. At the end of the predetermined period (two minutes) a relay MP is operated for a short interval. It first zeroises a relay-chain MR-MW (memory chain) and then at contacts MP3 applies earth to contacts MA2-MF2 to operate relays in the memory chain corresponding to the impulses stored in the full time chain AM-MF, the operated memory-chain relays locking over their lower windings as relay MP relapses. A relay MO is momentarily operated shortly after MP to release the operated relays in the "full time" chain which then commences counting the metering impulses for the next two minute period. Contacts MW2-MR2 of the memory-chain mark leads connected to the associated transmitting equipment, the value stored in the memory-chain being transmitted in known manner to the central station as MP releases. The memory-chain holds its reading until the end of the next two minute period, when, as above described it is reset according to the new reading of the full-time chain which is then transmitted as MP releases. This sequence is repeated at each two minute period, provided that the meter rate does not vary appreciably. A further binary relay chain AMG-MN, the quarter-period chain, counts the metering impulses in a manner similar to that of the full-time chain, for each quarter period, being reset at each half minute by the relay MO which is actuated momentarily at these intervals over line 9. Shortly before relay MO operates, an impulse is applied over line 8, and contacts MP1, MO7 to a combination of contacts of the quarter-period chain relays interconnected by lines 1-6 to contacts of the memory-chain relays. The effect of this contact arrangement is to multiply the quarter period chain reading by 4 and compare this value with that stored in the memory-chain. If the values thus compared disagree by more than 25 per cent, " half-way " relays MQ, MH are operated singly or together dependent on the degree and sense of the disagreement. The relays MQ, MH represent, respectively, a number of impulses corresponding to quarter full scale and half full scale of the receiving meter at the central station and the comparison conditions under which they are operated is tabulated in the Specification. An operated " half-way " relay locks over contacts MO1, operates the start circuit for transmission to the central station at MQ2, or MH2 and zeroises the memory-chain at MQ3 or MH3. When relay MO operates shortly afterwards the operated "half-way" relay or relays deenergize(s) and release(s) slowly during which time relays in the memory-chain are operated over MO6 dependent on the operated "halfway" relays. As MO releases the operated memory relays lock and cause transmission of a quarter scale, a half scale or a three-quarter scale reading to the central station according to whether the "half-way" relays MQ, MH are operated singly or together, the reading transmitted giving an approximate indication to the control station of the trend, faster or slower, of the meter in question. Four possible transmission conditions may arise at each two minute period, which are tabulated in the Specification. To cater for the condition in which a large change takes place in the 3rd quarter and is maintained in the 4th so that the total in the full period relay chain is appreciably less than that shown in the memory-chain, i.e. that corresponding to the 3rd quarter count, a pulse is applied to a lead 7 at the beginning of each two minute period after MP has operated to transfer the full period count to the memorychain, so that relays MQ, MH are operated to transmit a 75 per cent full scale reading rather than the full period count. The full-time period and the sub-multiple period may be varied, and transmission may be suppressed if a full-time count is exactly the same as that stored previously in the memory-chain.