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This paper describes the principles, applications of instruments most commonly used in medical engineering. In order to measure and record potentials and current is carried in the body by ions, it is necessary to provide some interface between the body and the electronic measuring apparatus. The physical quantity, property or condition that the system measures is import-ant because it may be internal(blood pressure), it may be on the body surface(electrocardiogram potential), it may emanate from the body(infrared radiation), or derived from a tissue sample(such as blood or biopsy) that is removed from the body. In an attempt to quantify the measurement of position of body organs, temperature of the body, motion of the skin and additional parameters from the living system, we have seen an increased application of technology to clinical and biomedical research. There are many methods used to convert physiological events to electric signals. Dimensional changes may be measured by variations in Resistance, Inductance, Capacitance. The series Resistance-Capacitance equivalent circuit breaks down at the lower frequencies, where this model would suggest an Impedance going to infinity as the frequency approaches DC. To avoid this problem, we can convert series RC to a parallel RC circuit that has a purely resistive Impedance at very low frequencies. Bioelectric potentials are produced as a result of electrochemical activity of a certain class of cells, knowns as excitable cells, that are componets of nervous, muscular, or glandular tissue.
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