3-channel ECG machine typically records three ECG leads simultaneously, providing a more comprehensive view of the heart's electrical activity compared to single-channel devices. Key specifications include a sampling rate of 1000Hz, a 12-bit A/D converter, and a frequency response of 0.05Hz to 150Hz. These machines often feature a thermal printer for recording and can be used in both manual and automatic modes. Safety features include defibrillator protection and low patient leakage current.