Patent GB-741810-A (GB)
Title: Improvements in or relating to bistable state circuit
Inventor: ISBORN CARL LYLE
IPC: H03K3/49
Filed: 1952-04-16
Abstract: 741,810. Non - contact - making relays. NATIONAL CASH REGISTER CO. April 16, 1952, No. 9526/52. Class 40 (4). [Also in Groups XIX and XL (c)] A bi-stable state reactive circuit comprises a capacitor connected in series with a first inductive winding wound on a ferro-magnetic core and permanently connected to an alternating current source such that the circuit assumes a low or high current condition, a first impulse triggering circuit containing a second inductive winding wound on the core for changing the current condition of the circuit, a second impulse circuit, connected in series with the first inductive winding, for changing the current condition of the circuit, and a third inductive winding wound on the core connected-to an output circuit having a voltage signal output indicative of the current condition of the circuit. The basic circuit (Fig. 1) includes the inductor L having a first inductive winding 2 wound on a small-core 3 of a metal whose permeability varies over a wide range with changes in flux density. With a low A.C. voltage (5 v.) applied, the current/frequency curve is substantially symmetrical, as shown in Fig. 2, since the inductance is constant. Increased current flows in coil 2 when the voltage is increased to 7 v., thus reducing the permeability of the core and hence reducing the effective inductance. The resonant frequency also increases. As soon as resonance is passed, decrease in current produces increase in inductance so that the curve falls more steeply than it rose. For a voltage such as 10 v., for which the change produced in the inductance is considerable, the current continues to increase and the inductance to decrease until resonance is reached. Then as soon as a decrease in current occurs (point a), the circuit becomes unstable, since the resulting increase in inductance produces a further decrease in current and so on, until the inductance reaches its original value (point b). If the frequency is then decreased, the current rises steadily until it becomes large enough to reduce the inductance (point. e), this tends to increase the current, which again reduces the inductance and the circuit again becomes unstable until point f is reached. Then with the lower value of inductance the frequency is below the resonant frequency and further decrease in frequency results in a decrease in current. Any pair of points such as g and h are possible points of operation in the region of bi-stability. If then an alternating voltage of 10 v. of the frequency corresponding to g-h is applied the circuit .will operate either at point g or point h, say g. A positive. pulse applied to lead 7 (Fig. 1) (the second impulse circuit), reduces the-current in 2 and the circuit then operates at point h. A positive pulse on lead 4 (the first impulse. triggering circuit containing the second winding 5), saturates the core, the resulting decrease in inductance causing the current to increase to that at point g. The output is taken from third winding 8. Triggered pair (Fig. 3). This comprises two circuits like that of Fig. 1 with a common load capacitor C3 whose value is such that only one of the circuits can have a high current flow at any one time. Operation is as follows: assuming Pa to be highly conducting (point g, Fig. 2), then, if coil 16 is pulsed, core 13 is saturated and the inductance of L2 is momentarily reduced. The increased current flow in Pb causes the voltage at point X to drop so that the current in Pa drops to that of point h (Fig. 2). A pulse on coil 15 will trigger the pair back. Binary counter (Fig. 4). The outputs of the triggered pairs are designated by A, the left output having a prime in each case, and the inputs by a, the left input designations including a zero in each case. Rectifiers such as D2 give D.C. outputs. Each input lead has a gating circuit 23 which ensures that points such as 25 go positive only when all the leads incoming to 23 are simultaneously positive. Pulses to be counted come in on lead I and are applied to all gates 23 but the pairs are operated in such manner as to count on the binary scale due to connections from the outputs of earlier pairs to the input gating circuits of the later pairs. A neon lamp, such as 28, glows when the righthand half of a pair is in the highly conductive condition, i.e. when that pair contains the digit one.