Patent GB-579979-A (GB)
Title: Improvements in and relating to electric circuit arrangements responsive to the rate of change of an input quantity
IPC: G05B1/02
Filed: 1943-03-05
Abstract: 579,979. Electric control systems. TUSTIN, A., and METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. March 5, 1943, No. 3664. [Class 40 (i)] [Also in Group XXXV] An electric circuit, among the uses of which is the stabilization of correspondence control systems, includes a temperature variable resistance, the current in which is increased or reduced from a polarizing value by variation in the sense of current or voltage input. In Fig. 1, temperature variable resistances TR1, TR2, having positive temperature coefficients, are in series with the supply to load L from source E. Polarizing current, large compared with the load current is supplied from source c, d. Source E may be (a) D.C. (b) A.C. with a period comparable with the time constant of the temperature variable resistances or (e) A.C. with a period small compared with the time constant of the temperature variable resistances. For (a) and (b) the polarizing source is D.C. while for (c) it is A.C. of the same frequency as and in phase or definite phase relation with source E. The effect of the circuit is to produce, in case (a) a change of load current, consequent upon change of voltage of source E, which is temporarily greater than the final change, in (b) a load current leading the voltage of source E and in (c) a phase advance of load currents corresponding to sinusoidal components in the amplitude of the voltage of source E. The Specification demonstrates mathematically that the circuit behaves, in some respects, like a capacity shunted by a resistance. In a modification, Fig. 2, each of the temperature variable resistances of Fig. 1 is replaced by an indirectly heated temperature variable resistance and its heater in series thus introducing a second time delay in the system due to the thermal capacity of the heaters H1, H2. Design of temperature variable resistances to produce the desired delay is discussed, one giving less phase advance with higher frequency inputs being described. Terminals e and f give a phase advanced output voltage if required. In a modification, Fig. 4 (not shown), each of the temperature variable resistance is in series with the heater of the other making the load circuit more sensitive to changes of input voltage. In this arrangement the voltage introduced into the load circuit by the temperature variable resistance circuit may even assist the input voltage. In Fig. 6 (not shown), the fixed resistances r, r<2> of Fig. 1 are ' replaced by temperature variable resistances thus giving greater change of voltage between terminals a and b for a given change of resistance. The modifications of Figs. 2 and 4 may be applied to this arrangement. An example of the use of resistances having a negative resistance temperature characteristic in a circuit similar to that of Fig. 4 is described in which the effect is opposite initially but subsequently, due to the indirect heating, the desired effect is produced. The Provisional Specification refers also to a series combination of resistances with positive and negative resistance/ current characteristics to improve sensitivity.