Design & Implementation of an Air Bubble Detector for a Hemodialysis Machine

Abstract

ABSTRACT The idea of the project is suggested to design and build an air bubbles detection unit by using new technique by electric capacitor. The motivation for making the project is based on the desire to deepen the understand of the principles for monitored detection units, the hemodialysis machine is chosen because it is widely spread and important in our country. The project includes complete information, schematic design circuit and conclusion for applying the capacitance detection method. The idea depends on the property of capacitance that relates directly with relative permittivity of the dielectric material. The project passes by several stages arranged as follows: First stage: building the capacitor manually to sense the changes of voltage, during the experiments we indicated that the capacitor detect "10pF" during pass air bubble. Second stage: building a bridge circuit which sensed about 0.1v during air bubble passes between the plates. Third stage: building the differential amplifier circuit that amplify the voltage difference by voltage gain 1000, and become 1v when air bubble passes. Fourth stage: building the comparator amplifier circuit that compares the voltage difference with reference voltage to operate the alarm circuit.