Patent GB-1335821-A (GB)
Title: Transfer function simulator
IPC: G06G7/625
Filed: 1969-07-03
Abstract: 1335821 Simulating system transfer functions JOSEPH LUCAS (INDUSTRIES) Ltd 2 Oct 1970 [3 July 1969] 33610/69 Heading G4G A circuit for simulating a transfer function, which can be represented as the ratio of two polynomials in D#d/dt, comprises a chain of identical modules, Fig. 1, each switchable as described below between two conditions, and a final module, Fig. 2, output terminals 01 to 05 of one module being connected to respective input terminals I1 to I5 of the next. Each module, Fig. 1, comprises an integrator 10 resettable by a pulse applied from terminal I6 to a F.E.T. 12. It also includes two invertor amplifiers 13, 14 acting as summers and a pair of coefficient potentiometers 18, 19, the output of potentiometer 18 being applied by switch 22 either to terminal 02 or 04 depending upon whether the coefficient is set negative or positive. Switches S and L are provided with sets of contacts S1 to S8 and L1, L2 and operate to change the circuit from a first condition to the second condition (which is the condition shown). The connections established in the two conditions are: (1) I1 to integrator; I2 to 04; I3 to 05; I4 to 02; I5 to 03: (2) I1 to the junction of resistors 23, 24; I2 to input of summer 14; I4 to input of summer 13; output of summer 14 to input of integrator 10; 03 to input of summer 14; 05 to input of summer 13; feedback of summer 14 is disconnected, and I3 is connected to earth via resistor 25. In the first condition, the summers 13, 14 may be connected to input terminals I7, I8 through switch L. The final module, Fig. 2, comprises two summers 26, 27, the latter being connected through a potentiometer 32 to an amplifier 34 with feedback variable by means of switch 36. Switch contacts E 1  determine whether there is any feedback from the output of amplifier 34 to the inputs I7, I8 of the Fig. 1 modules. A multivibrator 40 provides an input signal through potentiometer 41 and a signal to the re-set terminals I6. The contacts E2, E3, E4 connect either the output of amplifier 27 or amplifier 34 to monitor terminals 38, 39. If Yo = A/B.Yi where A and B are respectively polynomials with terms a i D<SP>i</SP> and b j D<SP>j</SP>, and Yo = #a i D<SP>i</SP>#, it can be shown that the term b n D<SP>m</SP># can be obtained from a chain of integrators by picking off from the output of each integrator a proportion determined by the coefficients b, summing these and subtracting the total from the input of the integrator chain. A term corresponding to b n  times the output is also subtracted from the input to effect division by b n  to produce D<SP>n</SP>#. These operations are effected by the potentiometers 18 and summers 13, 14 (Fig. 6), respectively for negative and positive signals. This figure shows an array of six integrators and is used to simulate a rational function comprising a numerator and a denominator both in the form of a product of three polynomials having respectively four, two and three terms. The separate terms of the product represent different components of a servo system. The input Yi consists of a periodic step function, the integrators being re-set by the multivibrator 40 after each cycle. The output is fed to an oscilloscope.