Abstract: In order to provide respective series of control signals for controlling separate items of apparatus, some of which may be redunant, there are provided a plurality of independently operable signal generators and a plurality of gating circuits connected to the generators and each operable to produce a respective control signal when it receives at least a predetermined number, dependent upon a chosen degree of redundancy of the generators, of correctly timed signals from the generators. Each generator is provided with a phase comparator type timing control device which adjusts the generator if its signals go out of synchronism with those of the other generators. The apparatus to be controlled can be a computer, a multiple-rectifier power supply or the like, and in connecting lines between various parts of the control apparatus and the controlled apparatus isolating devices can be provided.