Utilising a fieldbus protocol in a water quality monitoring system

Abstract

This thesis presents a new water quality monitoring system developed at the University of Durham in conjunction with Partech Instruments Ltd. The system uses a fieldbus protocol to create an open, distributed control network, replacing the dedicated products currently offered. Echelon LonWorks has been used to create three nodes: a suspended solids sensor, a general-purpose interactive monitoring tool, and a universal relay setpoint module. When connected, these nodes provide a means of activating relays when the suspended solids level reaches a definable level, while providing a numerical display for the operator. The sensor may be calibrated for a number of different applications. The sensor uses infra-a-red light to monitor the light absorption and 90 scatter within the solution. By dynamically adjusting the intensity of the emitted light, the sensor is able to increase its range over conventional devices. Signal processing, linearization and calibration operations are carried out within the sensor software. The final measurement is communicated as a LonWorks network variable, allowing the sensor to be treated as an interoperable device. Several third-party products have been connected to the network and a high degree of interoperability demonstrated. Three network management software packages have been investigated, and their suitability assessed. The final prototype system shows the power, flexibility and cost-saving that a fieldbus protocol can provide in an industrial control environment.