GB1416237A - Electronic controller with remote adjustment - Google Patents

Abstract

1416237 Gain control; pulse modulation circuits FOXBORO CO 30 Jan 1973 [14 March 1972] 4614/73 Headings H3T and H4L [Also in Divisions G3 and G4] Fig. 1 shows a pulse generator for switching an FET 14 in an integrator; the pulses are of constant width, spaced by an amount depending upon an analogue control voltage applied at 17. This voltage is amplified at 18 and integrated at 19; 25 provides bias. The output of 19 steadily becomes more negative until it exceeds a value from divider 20, which causes a comparator amplifier 21 to saturate positively, resetting the integrator by transistor switch 22 and providing an output pulse at 15. This lasts while a feedback capacitor 23 discharges through divider 20 sufficiently for the comparator to again change state, thus producing an output gap while integrator 19 is operating. Thus the pulse width depends upon the components 20, 23 while the gap depends upon the integration time and hence voltage 17. Fig. 3 shows an amplifier in box 25 whose gain may be adjusted by altering the on/off ratio of periodically operated transistor switches 27, 28 connected as shown in the feedback and input circuits of an operational amplifier 26, 29 is the amplifier input and 30 its output. The transistors are switched in complementary fashion by pulses on line 31 which have the constant frequency of a sawtooth generator 34 but whose mark space ratio depends upon a control voltage applied to 32 and compared with the sawtooth in comparator amplifier 35. Both of the devices are used in an automatic process control system (see Division G3).