Development of a novel ultrasound monitoring system for container filling operations

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Griffin, S.J., 2000. Development of a novel ultrasound monitoring system for container filling operations. PhD, Nottingham Trent University.

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Abstract

Current methods for measuring the liquid level in containers are often carried out downstream of the filling operation. While these methods meet the requirements of Trading Standards Legislation, they contribute very little to improving the real-time control of the filling process. Among the measurement techniques involving the use of non-invasive sensors, ultrasound has attracted an increasing level of interest in its application in the food industry because of its inherently safe characteristics. The aim of this research was to explore the utilisation of ultrasound measurement techniques in the development of real-time fluid level monitoring system.

Most of the previous research developing fluid level measurement techniques has focused on developing ultrasound monitoring systems with sensors positioned at the base of the container for ease of operation. The objectives of the current work was to explore the potential benefits of mounting the sensors on the side and top of containers and explore the possibilities of integration of ultrasound sensors with dispensing valves to maximise the efficient use of space, particularly where ease of access is restricted.

The present research programme has sought to develop an ultrasound monitoring system for container filling in both static and dynamic operations. For these studies, a static laboratory-scale container filling system was developed and utilised. The performance characteristics of the filling system were investigated in order to enhance the response time of an ultrasound monitoring system.

The key results of this work are the utilisation of an air transmission approach to ultrasound sensing as opposed to wall resonance and far wall echo approaches requiring contact transducers. This research has shown that the distances that can be measured using air transmission under ideal/experimental conditions are within expectable tolerances. To this end research involved construction of specific piezoelectric sensors and development of novel methods of data interpretation using a threshold approach to gain time-of-flight measurements.

It has been possible to characterise the effects of filling/environmental variables on ultrasound signal in a carbonating procedure (gas, gas mixtures, temperature, and pressure). Utilising known temperature/ultrasound signal characteristics temperature effects were obviated through the design and development of specific software. An increase in carbon dioxide content caused a reduction in signal amplitude (attenuation) and an increase in the time of flight measurement responding to a change in speed of sound. Pressure had little effect on the time of flight measurement but an increase in environmental pressure increased the ultrasound signal strength.

Surface plots were designed to build signatures of the relationship between pressure, carbon dioxide content, ultrasound signal amplitude and time of flight measurement, so that they may be incorporated into a control strategy.

The actual environment of a carbonated soft drink when filling was investigated, utilising carbon dioxide and nitrogen flushing in order to purge the system of oxygen. In addition, the research investigation has indicated that the custom built equipment for air transmission analysis could define minute quantities of gas and could therefore be applied to gas analysis.

The major conclusion from the research undertaken was that the novel application of ultrasound within the carbonating environment was capable of determining fluid level changes within expected levels of accuracy.