Abstract: A time-proportioning control system is disclosed for controlling an on-off solenoid valve of an earth-working machine, the system having a sensor responsive to an external reference for producing an error signal, an amplifier switch for switching on and off the on-off solenoid valve in response to the error signal and a capacitive feedback circuit connected from the output to the input of the amplifier switch for controlling the on and off times of the solenoid valve dependent upon the magnitude of the error signal.

Abstract: A process controller for diameter control in drawing optical fibre preforms consists essentially of the parallel arrangement of two output amplifiers, one providing low gain at low .+-. input voltages, while the other has high gain at high .+-. input voltages and effectively zero gain at low .+-. input voltages.

Abstract: The generator includes an input terminal, an output terminal, and three channels connected between the input and output terminals. The first channel contains a first amplifier and a first FET switch connected in series between the terminals. The second channel contains a second amplifier and a second FET switch connected in series between the terminals. The third channel contains an adjustable resistor and a third FET switch connected in series between the terminals. An adjustable bias signal positively offsets the output signal of the first amplifier and negatively offsets the output signal of the second amplifier to produce a signal deadband. When an applied input signal lies within the deadband, a signal from the resistor lies between the amplifier output signals, and a pair of comparators turn on the third FET and turn off the first and second FET's. This produces an output signal which follows the input signal with a gain determined by the resistor adjustment.

Abstract: An interface circuit for a transmission line between a remote transmitter and a central control room instrument includes an operational amplifier. The input of the operational amplifier is derived from the current drawn by the remote transmitter. The output signal of the operational amplifier is applied to control the operation of a transistor current controlling amplifier. The current controlled by the transistor amplifier is drawn from the same source as the current drawn by the transmitter. Because of a feedback connection from the transistor amplifier to the input of the operational amplifier, the output current from the transistor amplifier is a mirror image of current drawn by the transmitter. With that arrangement, both the power supply and the remote transmitter may be grounded without loss of accuracy or reliability.