This paper describes a circuit which can be used to control the sweep of an electromagnet between preset field limits and provide sychronizing pulses for a signal averager. Two operating modes are provided: manual and automatic. In the automatic mode the field sweeps continue indefinitely between the two preset limits. In the manual mode, the sweep is terminated when a field limit is reached. The controller requires an input voltage proportional to the magnetic field which can be easily obtained from a Hall probe.