Prototype for real-time adaptive sampling using the fan algorithm.

Abstract

Retrospective studies have established that the fan algorithm is an effective means of acquiring high-quality digital cardiac measurements. A prototype has now been constructed that samples adaptively in real time. The prototype uses two Texas Instruments TMS32010 signal processors and 79 additional TTL integrated circuits, at a component cost of approximately US$1000. The device acquires transient samples of the incoming analogue signal at up to 16000 samples s−1, selects samples from this input stream according to the fan algorithm, and transmits the samples and the time intervals between them at a fixed permanent rate. The permanent rate is between 100 and 400 samples s−1, as selected by the user. To respond to changing waveforms and repetition rates, while maintaining a fixed transmission rate, the prototype varies the fan tolerance. The lowest fan tolerance that will allow transmission of samples and time intervals at a rate not exceeding the permanent rate is used. If permanent samples at uniform intervals result in lower peak error than the fan samples, the prototype transmits the uniformly spaced samples instead of the fan samples. Results with test and real signals show that the device performs as designed and can accurately measure fast waveforms at low average sampling rates. For example, bipolar pulses 350 μs in duration were recorded with permanent rates of only 400 samples s−1, and cardiac signals were measured with 10–390 times lower peak error than would have resulted from uniform sampling at the same average rates.