Intelligent instrumentation

With the falling cost of microelectronics, intelligent instruments are increasingly used in process control. They are designed to integrate into data networks such as Fieldbus, so that remote users can access internal values and reconfigure their function. It is argued that such instruments should exploit models of the plant's data generation to achieve optimal filtering, of their own internal behaviour as verified by self-testing, and of the user's needs. A figure-of-merit for sensor signal processing is defined, and some fundamental results indicating the benefit of appropriate signal models are deduced. The value of validation, in which diagnosed faults affect the measurement status and its uncertainty, is emphasized. Examples of a self-validating thermocouple, a dissolved-oxygen sensor and a flow-control valve are described together with some guidelines about practical implementation.