1.

EEG machines have notch filter sharply tuned at _______ Hz as to eliminate mains frequency interference.(a) 10(b) 30(c) 50(d) 70The question was asked during an internship interview.Query is from Measurement of Heart Rate in chapter Patient Monitoring System of Biomedical Instrumentation

Answer»

The correct CHOICE is (c) 50

Easiest explanation: EEG machines have a notch filter sharply tuned at 50 Hz so as to eliminate mains frequency interference. These however have the undesirable property of ‘ringing’ i.e. they produce a damped oscillatory response to a square wave CALIBRATION waveform or a muscle POTENTIAL. The use of notch filters should preferably be restricted to exceptional circumstances when all other METHODS of eliminating interference have been found to be ineffective.



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