This thesis describes an investigation into the suitability of pulse frequency modulation (PFM) as a standard form of signal for representing quantities in process control. The encoding and decoding of PFM signals into both analogue and digital forms is examined in some detail. PFM is shown to be well suited for high accuracy telemetry at moderate cost, provided ample channel band-width is available. The processing of the information in PFM signals by means of binary logic devices is treated systematically. Functional building blocks are identified, and shown to be capable of performing all the basic algebraic and differential operations needed for control. The thesis concludes with an examination of applications and a discussion of PFM transducers, actuators and hierarchical control schemes. The performance constraints of two different process controllers are identified. Both controllers show ‘P+I’ action; one works continuously, the other has a cyclic action; both employ PFM techniques. They are shown to offer dynamic responses similar to those of conventional analogue controllers, in conjunction with high accuracy (e. g. errors less than ½%), computer compatibility and the facility for digital display.