Microprocessor-controlled signal generator for the functional testing of electrocardiographs

The main concept of the microprocessor-controlled signal generator is that the measurement and recording is done on the paper of the electrocardiograph under test. The signal generator provides signals of an amplitude and pattern which are suitable for determining the response of the electrocardiograph under certain conditions. For the sensitivity test, for example, the signal generator supplies a 1 mv square-wave pulse of duration 0. 2 s at a rat of 1. 2 per s. Ten signals (corresponding to the standard electrode potentials of the 12-lead ECG) emerge from the signal generator and enter the electrocardiograph through the usual patient leads. The unit can therefore be used for both single and multichannel electrocardiographs. Four independent signals are necessary to provide suitable outputs on three channels simultaneously, e. g. Leads I, II and III. A digital design was selected at an early stage for its versatility. Signal amplitudes vary from 50 mu v for the minimum signal to over 1 v for the common mode rejection ratio test. Eight-bit resolution is sufficient for this application provided that the signals can be attenuated independently. The fastest signal for output is a 100 Hz sine wave which is generated from the data in look-up tables. A simulated ECG is provided, the rate of which may be varied (and displayed) over the range 10-250 beats per min to an accuracy of plus or minus 1 beat per min. Fifty-nine tests are implemented, test selection being effected by pushbutton switches. All the tests are based on the Draft British Standard for the performance of single-channel and multichannel electrocardiographs.