Patent GB-845291-A (GB)
Title: Improvements relating to electrical circuits
Inventor: REDDING ROBERT JAMES
IPC: G05B11/01
Filed: 1956-11-19
Abstract: 845,291. Valve amplifying circuits. EVERSHED & VIGNOLES Ltd. Nov. 7, 1957 [Nov. 19, 1956], No. 35336/56. Class 40(6). [Also in Groups XXXV and XXXVI] An electric circuit providing an output voltage dependent on a quantity to be controlled or indicated comprises a device responsive to the quantity to control a direct current in the circuit, and a full-wave rectifier supplying the direct current and having the primary winding of a current transformer in its A.C. input circuit, the desired output voltage appearing across a resistance in the transformer secondary circuit. Fig. I shows the basic circuit in which the grid voltage of valve 1 controls the direct current drawn from rectifier 2, the current transformer 5 and a further rectifier 9 producing a voltage across resistance 10 which is proportional to the current through valve 1. Fig. 2 (not shown) illustrates the use of a second primary winding on transformer 5 to compensate for losses in rectifier 2. Two circuits may be used in cascade for greater amplification (Fig. 3, not shown) with a negative feedback to improve linearity. Figs. 4 and 5 show the circuit applied to time integration and differentiation respectively of the input signal; by choice of the values of resistors 43 and 58 the feed-back voltage across them is made equal to that across condenser 41 and resistor 57 respectively so that linearity of integration and differentiation is maintained as the voltage across 41 and 56 varies. Figure 6 shows a controller giving an output with components proportional to error and to the time integral and differential of error. The quantity is applied as a torque to a lever 72 by spring 73, and this torque is balanced by that due to a coil 74 carrying the anode current of valve 81 and moving in the field of magnet 75, the balance being obtained by contacts 76-78 adjusting the voltage across condenser 83 in the grid circuit of the valve 81. The anode current of 81 thus represents the quantity; it is indicated by meter 85 and converted by unit 90 (which consists of those parts of Fig. 1 enclosed in broken lines) into a Voltage V m . V m  is applied in opposition to V d  (representing the desired value, and derived from a stabilized supply and indicated at 95) and the error signal difference applied to valve 100 (96 and 103 allowing coarse and fine sensitivity control). The "zero-error" current of 100 is supplied from 101 so that the current through 103 represents the error, and the voltage across 103 is integrated by a circuit of the Fig. 4 type (integrating components 104-106, 108 adjustable by switches 107, 109, valve 115, unit 116 and feedback resistor 118). The error signal also appears at the output of unit 120 and this is differentiated by components 124-127 and the time differential applied to integrating condenser 104-106; it is stated that the effect of these connexions is that the anode current of 115 includes components porportional to the time differential and integral of error. The current of 115, and that through 103, representing the error, together flow through a regulator 134 (e.g. a flow control valve).