Patent GB-563276-A (GB)
Title: Improvements in indicating instruments
IPC: G06G3/00
Filed: 1942-07-06
Abstract: 563,276. Thermometers. GOULD, R. H. July 6, 1942, No. 9353. [Class 97 (iii)] [Also in Groups XIX and XXXVI] In an indicator, movements are imparted logarithmically to indicating means in accordance with variations in the magnitude of physical quantities, at least one of the movements being imparted by electromagnetic driving means including or directly actuating members formed to impart the necessary logarithmic movement, the logarithmic movements being added or subtracted so that the indicating means indicate at any given time the product or quotient of the physical quantities. The volt-ammeter of Fig. 1 indicates the product of volts and amperes of an A.C. supply, in which terminals a<7> are connected to the secondary windings of a potential transformer so that sector a<5> rotates dial a<2> carrying index a<8> for indicating the voltage on fixed logarithmic scale a<1>, while terminals a<22> are connected to the secondary of a current transformer so that disc a<14> rotates cam a' connected by metal tapes to cam a<17> to give a logarithmic rotation to pointer a<9> indicating on fixed scale a the amperes and on scale a<4> carried by dial a<2>, the product. The ohm-meter in Fig. 3 is in circuit with a resistance R which is to be measured, the total resistance of the remainder of the circuit being one ohm and being allowed for in marking the logarithmically arranged dial d<3> rotated by the moving coil d<3> of a voltmeter, the poles of which are distorted to make the movement logarithmic. A millivoltmeter E, acting as an ammeter drives cams d<8>, d<9> connected by metal tapes to rotate pointer d' logarithmically, and so indicate the value of resistance R on dial d<3>. This principle is applied in Fig. 6 to a level indicator, in which a float n<11> moves a contact arm n<2> over a rheostat so that the resistance is equal to the antilogarithm of the depth of liquid. Making allowance for a suitable known resistance R, the meter pointer moves logarithmically according to the resistance of the rheostat, so that the dial is graduated evenly. A straight drive from the float to the rheostat is described with reference to Figs. 7 and 8 (not shown), in which the variation of the resistance is obtained by increasing the diameter of the core. A quotient meter, Fig. 9, for indicating the temperature of the rotor windings of an alternator, also indicates the voltage and amperage of the current passing through the windings. Logarithmic scale z<2> is graduated in ‹C. of temperature, it being assumed that resistance varies directly with temperature, and is moved according to the amperage indicated on scale z by index z<5> Double-ended pointer z<8> rotates according to the logarithm of the voltage and indicates at z' the voltage on a fixed scale, and at z<8> the temperature. Fig. 10 and Figs. 11, 12 (not shown) show a modification of Fig. 3 in which the drive from the ammeter to pointer d<7> includes an idler gear d<34> which is cut helically and is slidable axially under the influence of the voltmeter, so as to divide the amperage by the voltage and to allow the use of a fixed scale d<3>. This system is further modified in Fig. 13; in which the drive from the ammeter proceeds via cam d<8>, arm d<51> and spring d<54> to pointer d<7>, the spindle d<52> of which carries a square iron plate d<56> drawn more or less towards a triangular iron plate d<57> carried by arm d<51> according to the logarithm of the voltage passing through coil d<59>. Yet another modification comprises a bimetallic strip incorporated in the pointer d<7> and heated proportionally to the voltage.