The waveform chart is a special type of numeric indicator that displays one or more plots of data typically acquired at a constant rate. The following front panel shows an example of a waveform chart.

The waveform chart maintains a history of data, or buffer, from previous updates. Right-click the chart and select Chart History Length from the shortcut menu to configure the buffer. The default chart history length for a waveform chart is 1,024 data points. The frequency at which you send data to the chart determines how often the chart redraws.

Displaying a Single Plot on Waveform Charts

If you pass the chart a single value or multiple values at a time, LabVIEW interprets the data as points on the chart and increments the x index by one starting at x = 0. The chart treats these inputs as new data for a single plot.

The waveform chart accepts the waveform data type, which carries the data, start time, and delta t of a waveform. Use the Build Waveform (Analog Waveform) function to plot time on the x-axis of the chart and automatically use the correct interval between markers on the x-scale of the chart. A waveform that specifies t0 and a single-element Y array is useful for plotting data that is not evenly sampled because each data point has its own time stamp.

Refer to the labview\examples\Controls and Indicators\Graphs and Charts\Waveform Graphs and Charts\Waveform Graphs and Charts.lvproj for examples of the waveform chart.

Displaying Multiple Plots on Waveform Charts

To pass data for multiple plots to a waveform chart, you can bundle the data together into a cluster of scalar numeric values, where each numeric represents a single point for each of the plots.

If you want to pass multiple points per plot in a single update, wire an array of clusters of numeric values to the chart. Each numeric represents a single y value point for each of the plots.

You can use the waveform data type to create multiple plots on a waveform chart. Use the Build Waveform function to plot time on the x-axis of the chart and automatically use the correct interval between markers on the x-scale of the chart. A 1D array of waveforms that each specify t0 and a single-element Y array is useful for plotting data that is not evenly sampled because each data point has its own time stamp.

If you cannot determine the number of plots you want to display until run time, or you want to pass multiple points for multiple plots in a single update, wire a 2D array of numeric values or waveforms to the chart. By default, the waveform chart treats each column in the array as a single plot. Wire a 2D array data type to the chart, right-click the chart, and select Transpose Array from the shortcut menu to treat each row in the array as a single plot.

Refer to the labview\examples\Controls and Indicators\Graphs and Charts\Waveform Graphs and Charts\Waveform Graphs and Charts.lvproj for examples of the waveform chart.

Waveform Data Type

The waveform data type carries the data, start time, and delta t of a waveform. You can create a waveform using the Build Waveform function. Many of the VIs and functions you use to acquire or analyze waveforms accept and return waveform data by default. When you wire waveform data to a waveform graph or chart, the graph or chart automatically plots a waveform based on the data, start time, and delta x of the waveform. When you wire an array of waveform data to a waveform graph or chart, the graph or chart automatically plots all waveforms.