MANY types of physiological applications require measurement of heartrate. Most of these are intended for clinical monitoring where accuracies are limited to 45 %. However, there are other instances, such as monitoring the rate of cardiac pacemakers, where a higher precision is needed. To calibrate or test ratemeters of high accuracy, a pulse generator must be employed whose error is at least one order of magnitude less than that of the ratemeter. The need to check calibration is particularly important for cardiotachometers that use reciprocation techniques based on the hyperbolic relation between R-R interval and the heartrate. Unfortunately, most commercially available pulse generators do not provide calibrated accurate pulse rates at the frequencies of interest. One device (JAMES et al., 1969) utilises the US 60 Hz mains frequency and a number of integrated circuits to provide calibrated pulse rates from 360 to 25 beats per minute (b.p.m.). Even though the mains frequency can be considered as a secondary frequency standard with an

K D Taylor

Papers

Precision cardiotachometer calibrator.