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ENCS

XY Graph — signal versus signal

The XY Graph plots one signal against another — the horizontal axis is not time but the value of a chosen X signal. It shines wherever the relationship between two quantities says more than their time courses: Lissajous figures, hysteresis loops (B–H, voltage–current, stress–strain), characteristic curves, or phase portraits.

Stress–strain hysteresis loop in the XY GraphStress–strain hysteresis loop in the XY Graph

The control accepts numeric scalar variables. Each curve point is formed from a pair of samples: a new sample of a Y signal is paired with the value of the X signal at the same instant — by the samples' timestamps (X is interpolated linearly between two samples), not by the order in which the data arrived — and the point (X, Y) is drawn. The curve is free to double back on itself — with a hysteresis loop, that is exactly the point.

Choosing the X signal

Drag the X signal and all Y signals onto the control just like on a regular graph. The first signal you drop becomes the X signal automatically (the X checkbox in the Signals tab ticks itself); every further signal is a Y signal on the first vertical axis. You can change the choice at any time by ticking the X column on another series — there is always exactly one X signal; its caption appears on the horizontal axis and it is not drawn as a curve. The remaining series are Y signals — several can be shown at once.

When you untick the X checkbox or remove the X signal, the chart clears and waits for you to choose a new X — no other signal is promoted to X on its own (that would silently change the meaning of the figure).

XY Graph settings — the X checkbox on the source seriesXY Graph settings — the X checkbox on the source series

Settings

The control's expandable section has three tabs:

  • General — Hor. legend (a horizontal legend), Title (the chart title), and Persistence ms (the age of points): the XY Graph has no time window; instead it keeps a rolling window of the last N milliseconds — older points disappear from the curve. A short persistence shows only the current loop, a long one lets the figure "settle" over several periods.
  • Signals — a table of series: X (the X-signal choice), Label, Visibility, Color, Width (line width 1–20), Style (line style — Solid, Dashed, DenselyDashed, Dotted), and Axis Id (assigning a Y series to a vertical axis — axes from number 2 are offered, the X signal is fixed to axis 1). On the X-signal row Visibility, Color, Width and Style are inactive — the X signal is not drawn. Remove a series with right click → Remove.
  • Axes — a table of axes: Id, Side, Label, Visibility, Color, and a range — AutoScale or a fixed Min/Max. Row 1 is always the horizontal X axis (it drives the caption, colour and range of the bottom axis; without a caption of its own the X signal's name is used), row 2 the first vertical Y axis — both exist from the start and cannot be removed. Add further vertical axes with right click → Add and remove them with → Remove; an axis used by a signal cannot be removed — the disabled item explains why in its tooltip (e.g. "The axis is used by: …").

Axis scaling

AutoScale (the default on all axes) works like an oscilloscope: the X and Y axes follow the minimum and maximum of the points currently in the persistence window — the range grows and shrinks with the data, with a small margin and rounded values. Switching AutoScale off freezes the last range and lets you enter a fixed Min/Max — also at runtime. Mouse zoom and pan in the chart are kept until you change the axis settings or the automatic scale is recomputed.

Context menu

  • Clear Graph — clears the drawn data,
  • Zoom to Fit — fits the axes to the current data,
  • Export Image — saves a snapshot of the chart (PNG, SVG…),
  • Export CSV — saves the series data to CSV,
  • Lock — locks the control on the workspace.

Tips

  • For the figure to make sense, the X and Y signals should be sampled in the same beat — e.g. a pair of values from one ECU DAQ event channel or from the same periodic event. Samples of one event share their timestamps, so they pair exactly.
  • The XY Graph reveals staircase shapes that a time course hides optically: if the X or Y signal is stimulated (bypassed from QInsight, changing only on each write), steps appear in the figure — not a chart error but a faithful picture of the signal. With bypass off the curve is smooth.
  • The control's settings (axes, signal assignment, which signal is X) are saved with the workspace.
  • It helps to keep the time course of the same signals next door in a regular Graph — the XY Graph does not show time.

Next

The instantaneous value in zones is shown by the Gauge.