Patent GB-731523-A (GB)
Title: Improvements in or relating to variable electrical resistances
Inventor: MCBRIDE MAURICE GRAHAM
IPC: G01R1/20
Filed: 1950-10-06
Abstract: 731,523. Measuring temperature; variable resistance and conductance networks; electric analogue calculating systems. SANGAMO WESTON, Ltd. July 5. 1951 [Oct. 6, 1950], No. 24498/50. Class 37. [Also in Group XXXVIII] .Relates to resistance and conductance networks adjustable in steps so as to simulate a non-linear law of the type Rt=Ro (1+-at-bt<2>) between a variable t and the 'resistance R. The invention is based or derived in accordance with the principle that the resistance/temperature curve of a resistance whose value varies uniformly with temperature t shunted by a resistance of constant value approximates to the required curve. According to a first aspect (Figs. 1 and 2), the invention provides a resistance network comprising two terminals (T1, T2) and two resistances (R1-R3) and (R4) connected in parallel with respect to said terminals and at least two control means (e.g. switches S3 and S4) calibrated respectively in terms of a different unit of said variable for varying a first one of said resistances (R3) in linear manner and at least one of said calibrated control means (S4) simultaneously varying the second one of said resistances (R4) in a non- linear manner. In Fig. 2 the switch S3 controlling the R3 or hundreds decade is ganged to switch S4 of step shunt resistor R4 so that a different value of shunt is switched in across the series three-decade combination R3, R2, R1 at each adjustment position of switch S3. Fig. 2 is calibrated for measurements from - 100‹ to +500‹ C. The negative values are measured by setting S3, S4 on the negative step (shown ringed) corresponding to - 100‹ C. and in effect operating S1, S2 in reverse against negative indices shown individually ringed in Fig. 1, e.g. - 100‹ C. is given by the S3 setting on the ringed negative in R3 with S2 at - 90‹ C. (or zero on the positive range) in R2 and S1 at - 10‹ C..(or zero on the positive range) in R1. According to a second aspect the invention provides a resistance or conductance network comprising two terminals (T1, T2), Fig. 3, two resistances or conductances (X and Y-X) connected between said terminals such that the resistance (R) or conductance between the said terminals is expressible in the form X(Y - X)/Y and calibrated control means (S1 and S2) for varying in a non-linear manner the total resistance or conductance in the manner that the resistance or conductance X is varied in a linear manner whilst maintaining constant the total resistance or conductance Y. In Fig. 4 the closed loop Y is translated into series resistors R4-R8 with R4, R5 in 10‹ and 100‹ C. steps respectively. The X100 switch S2 may be connected to junction x between R7/R8 with x chosen such that R7=R6 minus the total resistance of R4 so as to provide a - 100‹ C. setting. A further arrangement, Fig. 5, has the closed loop Y comprising decade boxes B1, B2 with similar denominations coupled so that B1 adds/subtracts as B2 subtracts/adds respectively and in equal increments. In Fig. 6, B is a decade resistance as described above and at bridge balance B indicates directly the temperature of the platinum resistance thermometer Rt. Fig. 7 is a conversion into conductances with B now C (conductance) in an opposite arm and using conductances it is shown that at balance (see Fig. 8) Rt=X(Y - X)/Y, where Rt represents a platinum resistance thermometer and conductance arm C comprises conductances X/K and Y-X/K in series (K=PQ). Conductances are switched in parallel for addition and to maintain Y constant while X varies a conductance is switched from shunting X to shunting Y-X. This is demonstrated in Fig. 9 wherein biriary-counting relays operate on change-over switches RS1-RS7 so that C1- C7 shunt Cx or Cy. Figs. 10 and 11 (not shown), illustrate decade-conductance networks with the total conductance Y held constant by step or bar switching controlling the required conductances. The invention is fully developed and explained mathematically throughout the Specification. The arrangements disclosed may be employed in a multi-range bridge type temperature indicator or recorder wherein the lowest step resistance or conductance comprises a motor-driven self-balance slide wire. Further temperature measuring applications consist in controlling the switches by a stepping mechanism provided with a cyclometer dial indicator or coupling the switches to printing heads for chart printing in time sequence.