Patent GB-905060-A (GB)
Title: Automatic range change circuit
Inventor: ANDERSON RALPH ARTHUR
IPC: G08C15/12
Filed: 1958-12-30
Abstract: 905,060. Electric selective signalling systems. PANELLIT Inc. Dec. 30, 1958, No. 42110/58. Class 40 (1). [Also in Group XXXVI] General.-In a monitoring system, the outputs of a plurality of transducers 1, 2, Fig. 1, are scanned by switch 4 and applied to a measuring system, which includes a selfbalancing potentiometer having an automatic range-change circuit, and controls a digital recording system. When, in attempting to balance the output of a transducer being scanned, the upper or lower limit switch 32 or 34 is closed by arms 30 on the potentiometer wiper, switch SRM-1 is stepped up or down and energizes one of range relays R7-R10. These relays have contacts R7-1 to R10-1 and R7-2 to R10-2 which, when closed, alter the potentials of the ends of the potentiometer wire with respect to earth, the potential difference between the ends remaining constant and corresponding, for example, to 399 units of measurement. The system may measure inputs varying between 0 and 1299 units in four overlapping ranges. The output shaft of motor 26 is coupled to digitizer 11 which has three discretely-positioned output shafts controlling ten - position switches 45, 47, 49. The contacts of tens and units switches 47, 49 are connected directly to the respective inputs of typewriter 20. Since a full deflection of wiper 23 corresponds to only 399 units, contacts 0-3 of hundreds switch 45 are connected to a network 16 including contacts of range relays K7-R10 arranged so that the appropriate lead 18 may be energized for printing the hundreds digit. A further bank 45<SP>1</SP> of switch 45 co-operating with contacts 10-3 of relay R10 provides the thousands digit " 1 " for the highest range of measurement. The wipers of switches 45<SP>1</SP>, 45, 47, 49 are energized in sequence by switch 53. Scanning non-identical and non-linear transducers, Fig. 3.-A group of range relays R3- R6, R11-R17 and R7-R9 is provided for each different type of transducer, e.g. ironconstantan thermocouples 2a<SP>1</SP>, 2b<SP>1</SP>, chromealumel thermocouples 2c<SP>1</SP>, 2d<SP>1</SP> (all having non- linear temperature-voltage characteristics) and pressure- or flow-responsive potentiometers 2e<SP>1</SP>, 2f<SP>1</SP> (having linear characteristics). To reduce the operating time of the system, range selector switch 65, coupled to switch 4, is arranged, in each of its positions, to energize that range relay which corresponds to the normal value of the output to be expected from the transducer being scanned. Switch SRM-1<SP>1</SP> then steps on to the contact thus energized and takes over control of the range relays to effect any changes in the range of measurement which may be necessary. To prevent erroneous indication when the output of a transducer being scanned lies outside the range catered for by its associated range relays, switch SBM-1<SP>1</SP> is prevented from stepping on to a group of range relays which is different from that containing the renge relay initially energized by switch 65. The range relays vary the range of measurement and correct the thousands and hundreds digits in a similar manner to that used in the system of Fig. 1, but relays R3-R6 and R11- R17 also compensate for the non-linear characteristics of thermocouples 2a<SP>1</SP>-2d<SP>1</SP>. The potentiometer is provided with equally spaced taps X-1 to X-5 and the selected range relay connects resistors across these taps, the transducer characteristic being regarded as linear over 100-unit sub-ranges.