medical electronics III

Analogue EEG instruments
Conventional analogue instruments consist of an amplifier, a galvanometer and a writing device. A galvanometer is a coil of wire inside a magnetic field. The output signal from the amplifier passes through the wire causing the coil to oscillate. A pen mounted on the galvanometer moves up and down each time the coil moves. The pen draws the trace onto paper moving below it.
The amplifier output is controlled by high and low frequency filters and sensitivity controls. The high and low frequency filter values will set the window within which the EEG activity is recorded. This is known as the bandwidth. The sensitivity controls the size of the activity displayed. For example a sensitivity of 10 µV/mm means that a signal with an amplitude of 100 µ V will produce a 1 cm vertical deflection.
The speed at which the paper moves on will also affect the appearance of the waveforms.