Abstract: The invention provides a system for detecting and analysing deviations from normal in the operating conditions of a process, for example a chemical manufacturing process. The system comprises transducers positioned to detect a plurality of operating parameters and generate signals representative of the said parameters. A processing device is connected to receive the signals and programmed to analyse the signals on the basis of a decision table having columns each of which represents a different combination of operating parameter values. Each column has associated therewith a value representing the seriousness of the deviation represented by the combination of values. Means are provided for displaying, storing and/or recording the nature of each deviation analysed by the processing device and the value associated therewith. Systems for transmitting data from transducers to a receiver and for analysing data are also provided.