Recording and processing of biosignals

Measuring is the experimental determination of a measured value by quantitative comparison of the measurand with a comparison value. The measured value obtained by this procedure is given as a product of a numeric value and a dimensional unit. It can be recorded continuously as a temporal variation of a physical value or discontinuously at particular moments. The deviation of the measured value from the measurand is the measurement error. It depends on the measurement procedure, the measurement device, and environmental effects. Systematic and random errors are distinguished. The measurement can be done directly or indirectly, depending on the chosen measurement procedure. For instance, the concentration of substances is determined by the measureable value extinction, ion activity, dielectric permittivity, or magnetic susceptibility. Here, the measurand is transformed into one or several intermediate values in order to further process the signal. The result of a measurement is the measured value itself or a combination of several measured values. This chapter covers the acquisition of different biosignals and the specifics of the measurement process in medical use.