Electronic controller with remote tuning

Claim 1

An electronic process controller responsive to an electrical measurement signal representing the magnitude of a condition of an industrial process and having an output circuit which produces an electrical control signal for operating a device associated with the process under control so as to maintain said condition at a desired set point value, said controller comprising in combination; adjustable means to develop a set signal representing the desired value of the controlled condition; comparison means for comparing said set signal and said measurement signal to produce a deviation signal indicating the amount by which said condition differs from said desired set point value; signal processing means having an input coupled to said comparison means and responsive to the deviation signal produced thereby, said signal processing means including proportional-band amplifier means and integral means interconnected with said signal processing means input to produce on the controller output circuit a composite output signal having both proportional and integral components; means for selectively setting the gain of said proportional-band amplifier means; said integral means comprising an electronic amplifier having an input and an output; a negative feedback circuit including integrating capacitor means coupling the output of said electronic amplifier to its input; an integrating resistor connected to said electric amplifier input; circuit means forming part of said signal processing means and connected to said integrating resistor to supply to the end thereof which is remote from said amplifier input a signal responsive to said deviation signal and thereby to direct to said integrating capacitor a current corresponding to thE current developed through said integrating resistor in response to said deviation signal; said integrating resistor and feedback capacitor means cooperating to develop at said amplifier output a signal representing the time-integral of the signal supplied to said resistor; means to couple said electronic amplifier output to said controller output circuit to provide thereto a signal including said integral component; electronic switch means connected to said integrating resistor and operable when actuated to interrupt said flow of current through said resistor; pulse-generating means coupled to said switch means for actuating said switch means so as to interrupt said current flow during the time of each pulse; and adjustable means coupled to said pulse-generating means to vary the frequency of said pulse without correspondingly altering the pulse duration, thereby to alter the effective timeconstant of said integral means and change the amount of said integral component in said composite output signal directed to said control device.