Modified on-off control

Claim 1

Control apparatus comprising: signal comparing means adapted to receive an input measurement signal and a set point signal and establish a first signal representative of any difference therebetween; signal summing means adapted to receive three input signals and establish an output signal representative of the sum of the three input signals; an oscillator adapted to provide an alternating signal; circuit means adapted to establish an output signal which is representative of the derivative of an input signal applied thereto; means to apply the input measurement signal to the input of said circuit means; means to apply said first signal, said alternating signal and the output signal of said circuit means simultaneously as input signals to said signal summing means; a control element having an input inpedance element therein; means responsive to the output signal from said summing means to establish a current corresonding to the amplitude of said output signal; and means to pass said current through said impedance element to actuate said control element.