Low-frequency response characteristics of three Grass model 7 polygraphs.
A low-frequency response analysis of three Grass model 7 polygraphs was undertaken. Observed error was generally found to fall within the manufacturer's stated range of +5 to -10% of DC signal height over the frequency range of human respiration (0.1-3 Hz), but this was not the case for frequencies greater than 6 Hz under certain circumstances. The magnitude of error was seen to vary directly with frequency and indirectly with pen-deflection amplitude and paper speed. The pen-oscillograph apparatus was the predominant source of low-frequency error, and this is probably due to pen inertia and pen friction on the writing surface. Two schemes to reduce such error are presented.
D002138:Calibration; D004868:Equipment Failure; D006801:Humans; D009991:Oscillometry; D010827:Physiology / Q000295:instrumentation*; D012119:Respiration