Measurement of the phase characteristic of Holter ECG system

A Holter ECG system should have a flat transmission characteristic within the frequency range necessary to reproduce ECG waveforms. In order to specify the characteristics it is necessary to establish methods to measure the characteristics precisely. The phase characteristic of Holter ECG system is difficult to obtain because of the lack of zero-phase reference. We devised a method to measure phase-shift characteristics in magnetic recording systems. In our method zero-phase reference is determined from a temporal plot of the frequency dependence of the phase-shift. This method was successfully applied to a Holter ECG system and reasonable results were obtained.