Abstract: An industrial process control apparatus and method that includes a number of processors and a number of input/output modules. Each processor is connected to a plurality of the input/output modules by a unidirectional command line. Each input/output module is connected to a plurality of the processors by a unidirectional response line. The processors are arranged to issue an identifier request to all of the connected input/output modules and each input/output module is arranged to respond to the identifier request via the respective response line with a response that includes a unique identifier. Such a configuration allows each processor to identify the physical location of each respective input/output module.

Abstract: This invention relates to line frequency synchronisation for use in diagnostics for alternating current electrical circuits. The invention provides a method of synchronising measurement system frequency with an alternating current line frequency comprising the steps of: adjusting the frequency of the measurement system frequency using a frequency locked loop until the measurement system frequency is within a predetermined range of said alternating current line frequency; and when the measurement system frequency is within a predetermined range of said alternating current line frequency adjusting the phase and the frequency of the measurement system frequency using a phase and frequency locked loop.