XY Plot+

Overview

XY Plot+ plots one measured value against another instead of against time, so you can see how two process values relate: head against flow, power against load, temperature against pressure. It adds fitted lines, reference curves, operating envelopes and a time trail to the scatter plot, and counts the points that fall inside or outside them.

XY Plot+ is a Vision Library+ symbol. The native XY Plot that ships with PI Vision is a separate symbol.

When to use it

Use this symbol when you need to:

• Show how one measurement responds to another, rather than how either changes over time.
• Pair several Y values with one X value, each X with its own sampling and time range.
• Fit a trend line and read its equation and R squared.
• Compare the live operating points with a manufacturer curve or count how many lie inside an operating envelope.
• Follow the direction of a trajectory, such as a start-up transient.
• Leave out the pairs taken while the equipment was stopped or outside a speed band.

Choose Combo Chart+ when time belongs on the horizontal axis.

Before you begin

• Choose numeric PI Points or AF attributes for X and Y. Non-numeric and bad values are dropped, not plotted at the axis minimum.
• Configure PI Web API for Vision Library+. The chart loads its own history.
• To convert units, use AF attributes with a unit of measure. A PI Point always shows its own units.
• For a curve or envelope, have its coefficients or its x,y pairs ready.

Add and set up the symbol

1. Select XY Plot+ in the PI Vision symbol gallery.
2. Drag the data source for the horizontal axis onto the display, then drag the data sources for the vertical axis onto the chart.
3. Right-click the chart and select Configure XY Plot+....
4. In the data sources section, select the first row. Use as is X. Every later row starts as Y.
5. Select each Y row and check that Pair with names the X.
6. Close the pane. Each Y appears as a series of points against the X, and the legend names each series.

Common tasks

Pair several Y data sources with one X data source

Use this when several measurements share the same X, or when one chart needs two X data sources with their own sampling.

1. Right-click the chart and select Configure XY Plot+....
2. In the data sources section, select the row for the X value (1) and set Use as to X.
3. Select a Y row (2).
4. Set Pair with (3) to the X. Every X on the chart is offered.
5. Leave Pairing on Timestamp and Method (4) on Interpolated. These read each Y at the X's own timestamps.

A Y with no X shows Unpaired and is not plotted. To plot a Y against its own window instead, for example yesterday against today, set Pairing to Position. To sample an X differently, select the X row and use its Data Retrieval group.

Add a regression line and read its equation

Use a regression to quantify how strongly Y follows X.

1. Select the Y row in the data sources section.
2. Expand Analysis and turn Regression on (1).
3. Choose the Model (2): Linear, Polynomial, Exponential, Logarithmic or Power.
4. Keep Show Equation (3) and Show R² (4) on.

The chart draws the fitted line (1) with its equation and R² at its end (2). The legend repeats them in an entry that follows the series (3).

A fit that cannot be computed draws nothing, and the point count notice states why. Save as Reference Curve copies a linear or polynomial fit into a reference curve, so you can keep today's behavior as a baseline.

Compare the points with a reference curve

Use a reference curve for a manufacturer curve or a design line, and count the points above and below it.

1. Expand Chart > Reference Curves and select + (1).
2. Enter a Label (2). The legend and the end of the curve show it.
3. Leave Type on Polynomial and enter the Coefficients (3), highest power first. The pane echoes the equation under the field.
4. Enter X Minimum and X Maximum (4). The curve is drawn over this range.

1. Turn Color points by this curve on (5).
2. To add a band around the curve, set Tolerance (6) to Absolute or Percent and enter the Value.

The points turn red above the curve, blue within the band and green below it. The legend states the count of each class.

Points outside the curve's X range keep their series color and are counted as Unclassified. Only one curve or line colors the points at a time. To mark a limit instead, add a reference line under Reference Lines: choose Axis X or Axis Y, enter the Value and turn Color points by this line on if you want the classes.

Count the points inside an operating envelope

Use a closed list for a permitted region such as a surge map boundary.

1. Under Reference Curves, select + and enter a Label.
2. Set Type to Closed List (1).
3. Paste the outline into Point List (2), one x,y pair per line, in order around the shape. The last point joins the first by itself.
4. Turn Fill on (3) to shade the region.
5. Turn Color points by this curve on (4).

The points inside turn green and those outside red. The legend reads, for example, Inside (962) and Outside (119).

A closed list needs at least three distinct points. A point exactly on the outline counts as inside.

Show the direction of change over time

Use the time trail for a hysteresis loop or a start-up transient. It colors the points by age and joins them in time order.

1. Set the display time range to a short period, such as 6 minutes.
2. Select the X row. Under Data Retrieval, turn Automatic Interval off and set Interval to 10 seconds, so the trail has few enough points to follow.
3. Expand Chart > Time Trail and turn Enabled on (1).
4. Turn Connect in Time Order on (2), then Direction Arrows (3).
5. Set Recent Points (4) to 5.

The points run from the Oldest to the Newest color, arrows show the direction, and the last five points are drawn larger.

The trail is not available while a multi-state attribute or a curve colors the points.

Keep only the pairs from one operating condition

Use a gate to leave out the pairs taken while the equipment was stopped, in another mode or outside a speed band.

1. Select the data source that states the condition, and set Use as to Gate (1). It is no longer plotted.
2. For a number, set Mode to Range (2) and enter Minimum (3) or Maximum. Leave one empty to leave that end open.
3. For a state, set Mode to State and type the state name exactly as the digital state set spells it, for example Running.
4. Turn Invert on to keep the pairs that do not meet the condition.

The pairs that fail the condition leave the plot. Set Toolbar > Reveal to Always to show the count of drawn pairs in the corner. Its tooltip lists the pairs excluded for each series.

With several gates, a pair must pass all of them. A pair with no usable gate value is left out. A gate with no condition filters nothing.

Use the symbol

• Hover a point to see its Y value, X value and time. When a multi-state attribute colors the points, its value is shown too.
• Hover a legend entry to fade the other points. Curves, envelopes and lines stay in view.
• Click a legend entry to hide that series, color band or class. Hiding changes only your view, and the counts and fits do not change.
• Zoom with the mouse wheel or the toolbar, and drag to pan or box zoom. Zooming never changes the display time range.
• Download saves a picture (PNG, SVG, PDF) or the paired data (CSV, JSON, XLSX). Curves, lines and fits are not exported.
• With a multi-state attribute or a curve coloring the points, the bands or classes replace the series entries in the legend.

Nothing in the chart writes data to the PI System.

Configure the symbol

The pane has these sections: the data sources section, Chart, Scales, Time Bar and Interactivity. Multi-state settings open from the chart's context menu.

Data sources

The list groups each X with the Y rows paired with it. Chips mark X1, X2, Y, Unpaired and G for a gate. Select a row to edit it, and use the delete button to remove it.

Chart

When several rules could color a point, the order is a Multi-State attribute, then a curve or line, then the time trail, then the series colors.

Scales

Time Bar and Interactivity

Troubleshooting and limitations

• Limitation: There is no fullscreen view, and no event frame or period overlay. To compare two periods, copy the chart and give each X its own custom time range.
• Limitation: Several gates are always combined so that all must pass, and a state name is typed, not picked from a list.
• Limitation: The trail's connecting line has one color. The end labels of horizontal reference lines are kept apart, but labels of curves, fits, vertical lines and Center labels that end close together can still overlap.