ABSTRACT
Whereas the time axis is generated by moving the chart at constant velocity, the ordinate can be marked in an analog or a digital manner. Analog recorder transducers generate a physical displacement of the writing device, e.g., a pen or a printhead. With digital transducers, moving parts are absent and the writing device is a stationary rectilinear array of equidistant writing points covering the complete width of the chart; the writing act then consists in activating the point situated at the site corresponding to the signal magnitude and putting a dot on the paper. Analog recorders thus can produce continuous lines, whereas digital recorders generate dotted lines. If ordinate and time axis resolutions are sufficient, digital recordings have excellent graphic quality regarding visual impression of continuity. Analog transducers can be used in a discontinuous mode and thus handle a set of slowly varying signals; during the scanning cycle a dot is set on the paper by the moving writing device at the sites corresponding to the magnitudes of the signal. A single digital transducer and a single analog transducer applied in the scanning mode can handle a set of signals; a single analog transducer can process only one signal in the continuous mode. For a digital transducer the number of signals recorded is essentially unlimited; it is thus programmed to draw the necessary calibration lines. With analog transducers calibrated paper is used. In this case, generally ink writing is applied and different colors ensure excellent tracing identifiability. With the digital array, dot printing can be more or less intensified for different channels or more than one adjacent points can be activated, resulting in more or less increased line blackness and thickness. However, tracing identification is usually performed by alphanumeric annotations.
