An Industrial Fluid Multi-Sensor

Determining oil quality is an important part of any industry that uses oil as lubrication. Over time oil quality degrades with use or from contaminants being introduced. Since the majority of systems that use oil are closed systems there is no way to remove contaminants or recycle the oil to its original state. The only option is to change the oil. Even with frequent oil changes there is still a chance that a contaminant can be introduced, causing a failure. Currently there are sensors that test oil quality, but they are bulky compared to a Microelectromechanical (MEMs) multi-sensor. The objective of this project is to make a low cost industrial fluid multi-sensor to replace larger sensors that exists today. The industrial fluids multi-sensor will measure; oil quality, water in oil and temperature of the oil. The quality of the oil will be determined by using Electrochemical Impedance Spectroscopy (EIS). This will be accomplished by using an interdigitated finger (IDF) electrodes to measure the impedance of the oil at different frequencies. With regular use and the introduction of other contaminants the resulting impedance changes, ultimately telling when your oil is old or contaminated and needs to be changed. Water in oil will also be tested. An IDF capacitor with a polyimide coating will be used to determine the water in oil. Water in oil is important to sense because the oil does not lubricate as well if water is present. The polyimide absorbs the water, which changes the dielectric constant of the polyimide and increases the capacitance as water is added. The detection of water can be used as an early indication that there is a leak or a broken gasket. Not fixing this problem can lead to a seized engine or non-uniform wearing of gears. The temperature of the oil will be measured with a thin film resistor. The thin film resistor changes resistance as the temperature changes. Depending on the thermal coefficient of resistance (TCR), a greater or less change in resistance will occur for different materials. Two revisions of the multi-sensor were designed, manufactured and tested at RIT. The EIS sensor and Temperature sensor were also tested by an outside company. One temperature sensor and 18 IDF capacitors made of tantalum were designed in Design 1. The IDF capacitors were used as either an EIS or water in oil sensor by adding polyimide. Design 1 had three major shortcomings that lead to Design 2. The first improvement was that all three sensors needed to put on one chip. Secondly, the nominal capacitance of the water in oil sensor needed to be increased. Lastly a different metal was needed for the temperature sensor because tantalum has either a positive or negative temperature coefficient of resistance. A new fabrication process was used to fabricate Design 2 to be able to get smaller widths and spaces of the IDFs. Two EIS, water in oil and one temperature sensor were designed in Design 2. All of the sensors in Design 2 were nickel on top of titanium. Quality of oil, water in oil and temperature were all able to be successfully tested using Design 2