1. Field of the Invention
This invention relates generally to the production of graphic displays of analog data signals, and relates particularly to such displays that are produced on the basis of intermittently obtained values or samples which represent successive amplitude conditions or values of the signals.
2. Description of the Prior Art
Graphic display apparatus for producing single or multi-channel analog indications and/or records of the amplitude variations of sampled data signals are known in the art. One such known form of apparatus has an undesirable characteristic, however, of producing or plotting each of the curves as a series of separated elements or dots instead of as a substantially continuous line or trace. As a result, the curves produced by such apparatus and the indications and/or records, are often difficult, if not impossible, to interpret and analyze. This is particularly true in the case of a plurality of superimposed or overlapping curves representing data signals having relatively high frequencies and/or irregular wave forms.
In another form of known prior art apparatus, single or multi-channel graphic displays are produced from intermittently sampled data by a so-called connected sampling method that yields substantially continuous, and hence more discernible, curves, notwithstanding the intermittent nature of the sampled data from which the curves are produced. In this form of apparatus, the curves representing the analog signals are obtained by producing successive substantially parallel lines on a display medium, each of the lines being substantially continuous and extending between two points, the positions of which represent, respectively, a corresponding two, consecutively derived ones of the sampled data values. Specifically, each parallel line comprises a line segment connecting the previous and the present values of the data signal. An example of a method and apparatus for producing such a connected sampling graphic display from intermittently sampled data is shown in U.S. Pat. No. 3,605,109. With this prior art method and apparatus, as long as the analog signal or signals are slewing in one direction or the other, there is little or no error in the graphic representation of the signal or signals. If the signal should undergo a very rapid or abrupt change of direction between two sample periods, however, significant peak errors can occur, in that such peaks will not be indicated or recorded. Thus, while graphic display apparatus of this type is extensively used in many applications, such apparatus is not suitable for use where it is desired to indicate and/or record abruptly changing or transient data.