Calibration of Elctrocardiograph (ECG) Simulators

Abstract

The Standards and Calibration Laboratory (SCL) in Hong Kong has set up a calibration facility for electro-cardio graph (ECG) simulators. ECGs are medical devices designed to measure the electrical signals associated with cardiac activity. They are used to diagnose heart diseases and arrhythmias, which are commonly used in hospitals, emergency facilities and medical institutes. Routine performance check of ECGs could be performed by ECG simulator. In order to ensure the accuracy of the instruments, calibration procedures which are traceable to primary standards or SI units are essential. At the SCL, the output signal from an ECG simulator is measured by a differential amplifier and a high speed digital sampling system. The system also includes a reference voltage source, an inductive voltage divider and a control computer. Digital sampling system enables the calibration of non-sinusoidal wave with high accuracy. Signal characteristics including signal amplitude, frequency and wave form could be evaluated by an in-house developed program for normal sinus rhythm waveforms as well as for ECG performance waveforms (sinusoidal, triangle, square and pulse). Since the test signal is in the sub-millivolt (mV) range, a differential amplifier with high common mode rejection ratio is used to amplify the test signal. The frequency response of the differential amplifier is calibrated by a reference voltage source and an inductive voltage divider, whereas the digital sampling system is calibrated against the laboratory's voltage and frequency reference standards. The developed calibration system is capable of measuring signals in the sub-mV level with test uncertainty ratio (TUR) better than 4. Details of the system configurations and the uncertainty evaluation will be described in the paper.