Patent GB-488706-A (GB)
Title: Improvements in and relating to the measurement of small electromotive forces and the automatic control of variable physical properties giving rise to the same
IPC: G05B11/01
Filed: 1936-10-09
Abstract: 488,706. Voltage and resistance measurements ; determining physical qualities of materials. STEVENSON, A. B., ALCOCK, T. C., and IMPERIAL CHEMICAL INDUSTRIES, Ltd. Oct. 9, 1936, No. 27498. [Class 37] [Also in Group XXXV] Apparatus for measuring small electromotive forces, and for the automatic control of variable physical properties, such as temperature or hydrogen-ion concentration, comprises a slide-wire potentiometer in series with and opposing the source of e.m.f., and a galvanometer with time-cycle chopper-bar mechanism, the differential potentials during the chopper-bar action being applied through a high resistance and valve amplifier grid circuit, a mid-point tapping on the resistor being connected to the cathode or point more negative. In Fig. 1, the source 20 to be measured, or upon which control is to be effected, is connected in opposition to slide-wire potentiometer 21, the differential potentials being connected across resistor 23 and valve amplifiers 26, 27. Galvanometer G is slidably connected to equipotential points on the anode loads 30, 31, and has a step-by-step chopperbar mechanism (not shown). In Fig. 2, equipotential points on the anode loads 30, 31 are connected to an inverter 32 driven by a synchronous motor 33, the inverter output being fed to the grids of gas-filled tubes 39, 40 through transformer windings 34.. 36 and resistors 37, 38. The output of the tubes 39, 40 supplies a servomotor M effecting control of the variable, and a cam may be inserted in the drive to obtain direct proportionality. This control is proportional to the instant deviation of the e.m.f., and further control can be effected that is proportional to the time-integral of such deviation, and also to the time-derivative, the complete control being given by the equation, V=k1##dt+k2#+k3d#/dt. The timeintegral term is obtained by a cam switch 46 making connection at 45 on the slide-wire for a given interval in a time cycle that is preferably different from that of the chopperbar mechanism, the galvanometer being disconnected during the integration period. The third term is obtained by changing for a given time period the resistance loads of the amplifier for highly inductive ones, the e.m.f. supplied to the inverter being then a function of the rate of change of the derivation. Windings 301, 302 and 311, 312 on cores of silicon steel, nickel-iron alloy or a nickel-cobaltaluminium alloy are formed in known manner as purely resistance or highly inductive elements for this purpose. In another control arrangement of temperature, a Wheatstone bridge connection of the unknown and potentiometer e.m.f's. includes a triode or pentode amplifier and a dynamometer with chopperbar mechanism. In this arrangement, the anode loads are connected through transformer windings and phase-advancing condensers to the gas-filled tubes supplying the servomotor. A time-integral term is obtained in the bridge connections similar to that in respect of the potentiometer circuit of Fig. 2. Specification 436,887 is referred to.