Patent GB-876876-A (GB)
Title: Automatic range change circuit
Inventor: SPERRY ALBERT FRANCIS
IPC: G01R15/09
Filed: 1958-11-20
Abstract: 876,876. Electric measuring systems. PANELLIT Inc. Nov. 20, 1958, No. 37447/58. Class 40 (1). [Also in Groups XIX and XXXVI] A measuring and recording system of the type in which the outputs of a number of transducers, representative of the values of measured variables, are cyclically connected to a self-balancing potentiometer whose wiper is driven by a motor which also operates an analogue-to-digital converter which is associated with a digital recording device, such as an electric typewriter, to produce a printed numerical record of the values of the variables, is characterized by the fact that the range of values represented by a single excursion of the wiper over the potentiometer is smaller than the range of values required to be recorded, and that switches, operated when the wiper approaches the upper or lower ends of the potentiometer, apply a higher or lower range of voltage to the potentiometer and correspondingly control the operation of the recording device, adjacent potentiometer ranges substantially overlapping, and the range of values required to be recorded being wholly covered by the smaller potentiometer ranges. Measuring apparatus.-As shown, Fig. 1, transducers 2a, 2b, &c. which may be, e.g. iron-constantan or chromel-alumel thermocouples, or bellows-operated potentiometers for measuring flow or pressure, are sequentially connected by a scanning switch 4 controlled by a timer 6 to a detector-amplifier 28, wherein the output of each transducer is compared with the potential with respect to earth of the wiper 23 of a potentiometer 10, the differential output of the detector amplifier 28 being fed to a motor 26 which moves the wiper 23 to a null position and also drives a mechanical analogueto-digital converter 11 to produce a digital output representative of the position of the wiper. The range of the potentiometer output is determined by a D.C. source 40 and the number of resistors 41, 42 which are connected between the poles of the source and the ends of the potentiometer resistor. If the transducer input to the detector 28 is outside the range of the potentiometer, the wiper 23 is driven to the upper or lower limit of its path where it closes a switch SRM (+) or SRM (-) to energize a relay to step, in one direction or the other, the wiper 36 of a stepping switch SRM1 in a range changing relay circuit 14, thus energizing one of four relays R7-R10 which closes contacts associated with resistors 41, 42 to alter the potential span of the potentiometer to the next upper or lower range, there being a substantial overlap in each case. Recording apparatus.-The output shafts of the digital converter 11 control the wipers of three ten-position switches 45, 47, 49, representing, respectively, hundreds, tens, and units. The tens and units switches are connected directly to the relevant channels of an electric typewriter 20, to prepare circuits for the energization of the latter. The contacts of the hundreds switch 45, only four of which are used in the embodiment shown, are connected to the typewriter 20 via a range correction control switch system 16 wherein contacts (not shown) of the range-changing relays R7-R10 close to connect each contact of the switch 45 with the type channel appropriate to the range being used. The wiper of a ten-position switch 451, which is ganged for movement with the wiper of switch 45, operates when relay R10 is energized to prepare a circuit via three of its contacts to the digit 1 channel of the typewriter 20 to provide a thousands figure in the record when the highest range of the potentiometer 10 is in use. Printing is effected by a programmer 51 comprising a switch having a wiper 53 and fixed contacts 54-59 which complete circuits to the type channels via the digital selector switches on being cyclically scanned when the programmer is triggered by a balance control 62 responsive to a null condition of the detectoramplifier 28.