 Reliability HotWire

Issue 108, February 2010

Hot Topics

Using the Chart Wizard to Create a Custom Plot

A wide variety of plots are built into the Weibull++ software, as well as the ability to combine separate data sets on a single plot using the MultiPlot. However, sometimes a desired plot is not available. For example, suppose that you want to plot component reliabilities and the system reliability obtained from a reliability block diagram on a single plot. In Weibull++, you can obtain the plot of the component reliability versus time in the Standard Folio, and the plot of system reliability versus time using the Diagram. You can then create a custom plot that combines these plots. This article will show the steps to create such a custom plot in Weibull++.

Consider the case of a system that consists of two identical components arranged reliability-wise in parallel. A set of failure data is collected for 5 specimens with the following times to failure in days: 29, 71, 74, 79 and 103. A Weibull distribution is fitted to the data and the parameters β = 2.3325 and η = 81.3094 days are computed. In addition, a Diagram representing the system is created and the system reliability equation is found to be: A table of component and system reliabilities is created in a General Spreadsheet for times from 0 to 60 days, as shown in Figure 1. Figure 1: Component and System Reliabilities for 0 to 60 Days

In order to use the Chart Wizard built in to Weibull++ to create a scatter (XY) plot with N series, each with M data points, the data must be rearranged into the format shown in Table 1, where S represents a series, and X and Y represent the x- and y-values of the data points.

Table 1: Data Format for Scatter Plot

 S1 Label S2 Label SN Label S1 X1 S1 Y1 S2 X1 S2 Y1 SN X1 SN Y1 S1 X2 S1 Y2 S2 X2 S2 Y2 SN X2 SN Y2 S1 XM S1 YM S2 XM S2 YM SN XM SN YM

Another table is created in the General Spreadsheet to rearrange the reliability data into this format, as shown in Figure 2. Figure 2: Component and System Reliabilities Ready for Plot

The steps to create the plot are as follows:

• Select all the cells that contain the series labels and the x- and y-values for the plot (in this example, cells E1 through H32).
• Click the Chart Wizard icon. • Click in the desired location for the top left corner of the plot and drag to the desired location for the bottom right corner of the plot.
• The Chart Wizard will appear. On the Gallery page, select to use 2D charts and select the XY (Scat) chart type, as shown in Figure 3, then click Next. Figure 3: Chart Type Options

• On the Style page, select the first chart style, as shown in Figure 4, then click Next. Figure 4: Chart Style Options

• On the Layout page, enter the Chart Title, Chart Footnote and add a Chart Legend, if desired, and then click Next. For this example, a legend was placed at the bottom of the chart, as shown in Figure 5. Figure 5: Chart Layout Options

• On the Axes page, enter the appropriate axis titles, if desired, and then click Finish. For this example, the Category (X) label was set to "Time" and the Value (Y) label was set to "Reliability," as shown in Figure 6. Figure 6: Chart Axes Options

Figure 7 shows the resulting plot of the component and system reliabilities as functions of time. Figure 7: Component and System Reliabilities on a Single Plot 