Use the XMR Chart Function
You can use the XMR Chart function to calculate a central line that remains constant. The central line is utilized to monitor the consistency and fluctuation of a process over a period of time. It comprises two distinct charts:
- Individual (X) Chart: Used to trace individual values.
- Moving Range (MR) chart: Used to observe the variation between consecutive measurements.
Review the following scenario for the XMR Chart function. Then, you will simulate PLC data and calculate the central line.
In a pharmaceutical production plant, consistent dosage in pill manufacturing is paramount for patient safety and regulatory compliance. High-precision scales measure the weight of individual pills, with data points collected at regular intervals.
The XMR Chart function is integral to this process, providing real-time monitoring of dosage weights. By establishing a central line from initial measurements and calculating moving ranges, the plant ensures each pill is within the stringent weight specifications.
Follow the steps to Connect a Device and configure the following parameters:
- Device Type: Simulator
- Driver Name: Generator
- Enable Alias Topics: Select the checkbox.
After connecting the device, add the following tag. See Add Tags to learn more.
- Name: Select S - Random value generator
- Value Type: Select float64
- Polling Interval: Enter 1
- Tag Name: Enter input1
- Min_value: Enter 101
- Max_value: Enter 199
You can now create the analytics flows using data from the device and tag you previously created.
To create an analytics flow with the XMR Chart Processor function:
- In Litmus Edge, navigate to Analytics.
On the analytics canvas, click Add processor. The Create a processor dialog box displays.
The Add processor option- Select DataHub Subscribe.
In the Topic field, click the Search icon, select the device you previously created, and then select the alias topic for the input1 tag.
Create a Processor dialog box- Click Save.
- Click Add processor again and select the XMR Chart processor. The Edit a Processor dialog box appears.
- Window Size: Enter a value that represents the range to apply the XMR chart function. For this example, we input a value of 100.
- Process Limit Multiplier: It is used to calculate the upper and lower process limits. For this example, we input a value of 2.66.
- TimeInterval: If you know your input is going to publish at the expected interval, it is better to disable this timer by entering 0 in the field.
Click Save.
Edit a Processor dialog box
- Connect the DataHub Subscribe processor (tag: input1) to the XMR Chart processor with a wire and use the events connection.
- On the analytics canvas, click Save. The configured analytics flows should look like the following:
Click the View icon in the XMR Chart processor to view the output values.
The output of the XMR Chart function shows a central line at 150.29, with an upper process limit of 229.14 and a lower process limit of 71.44.
Once the window is filled, other fields that are calculated as follows:
- Moving Ranges: Difference of successive values.
- Average Moving Range: Average of the moving ranges.
- Process Limit Multiplier: Calculates the upper and lower process limits.
- Upper and Lower Natural Process limit: Calculated by taking the product of process limit multiplier and average moving range, and adding/subtracting it from the central line.
In some cases, the central line is adjusted. Here are the cases:
- If current value is outside the process limits multiple times in a row.
- If the multiple values in a row are closer to either limit than they are to the central line.