ECG interference suppressed using a harmonic generator

Non-linear loading of the utilities supply introduced significant electromagnetic field (EMF) interference severe enough to disrupt electrocardiograph (ECG) monitoring and recordings in the new Emergency Department (ED) at the Royal Melbourne Hospital (RMH). This interference was evident even though standard Mu-metal shielding had been installed over the main hospital power feed which runs underneath the department. Investigations revealed that the source of the interference was due to 3^rd harmonic currents flowing in the mains cable. This interference was suppressed by introducing third harmonic current into the main power cable in anti-phase to the interfering signal.