Measurement System to Monitor Interface Level Between Oil and Water in a Rapidly Rotating System

Abstract: Alfa Laval is a market leader in centrifugal separators that develops and sells separators for a wide range of uses. Clarification of beer, wine, water purification, drug production and purification of marine fuels are just a few of the hundreds of different uses for Alfa Laval separators. To further optimize their separator performance, Alfa Laval is interested in the development of a measurement system, which can find the interface position between the lighter and the heavier liquid phases inside the separator. The aim of this thesis work is to develop such a system that can measure this interface position and wirelessly transmit its value. Thesis work begins with a literature review of capacitance and ultrasonic measurement systems to find out their advantages and disadvantages. It was observed that a single measurement method will not provide the necessary results and therefore more than one measurement system was required. To limit the work in this thesis, only one technique, namely an ultrasonic measurement system was developed. The ultrasonic measurement system was divided into three parts, the transmitting circuit, the receiving circuit and the ultrasonic transducer. A FPGA was used for the generation of pulses of very small width for the transmitting circuit and for calculating the time of flight of the acoustic wave. Further, for wireless transmission of interface position, a microcontroller was used along with a wireless module based on zigbee. The developed ultrasonic system was tested in a water container and in a settling tank. In the water container, water steel and water air interfaces were observed and tests were recorded. For testing in a settling tank, oil and water interface was obtained and tests were carried out. The transducer showed good sensitivity for the steel and the water and likewise for the air and the water interfaces.For the measurement of the oil and the water interface in the settling tank, very weak signals were observed and the only significant peak observed was presenting the oil and air interface. It has therefore not been possible in this thesis work to obtain the oil and the water interface. Thus, either the sensitivity of the transducer should be increased or the voltage level of the transmitting signal should be increased in order to achieve good sensitivity for the oil water interface.