Customizing control limits
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Prerequisites
- Access to the Management > Collection planning (SP003) menu or to the Management > Collection tracking (SP004) menu.
- Planned collection.
Introduction
Control limits help distinguish the normal variations of a process from those caused by failures or deviations. When the data of a process exceed these limits, it means that the variation is not random and may result from a problem that needs to be resolved.
The configuration covered in this article will provide guidance as to how SPC must calculate the control limits of the characteristics. By default, the system is configured with the "Fixed calculated limits" option, but there are other options available.
Follow this tutorial to carry out this step:
Customizing control limits
2. Select the desired collection and click on the 
button.
3. In the Characteristic section, select a characteristic and click on the button.
- Fixed calculated limits: the system calculates the control limits based on the provided samples. Thus, it is necessary to enter at least two samples in the collection.
- Variable calculated limits: the control limit calculation is based on the number of filled out readings, generating a limit in the form of a plateau, instead of a straight line. Option suitable for when not all sample readings have been filled out.
- Fixed limits: allows the user to set limits as needed. In this option, it is necessary to define the lower control limits (LCL) and upper control limits (UCL) for the average (X), range (R), and standard deviation (S) charts. It is also possible to specify an objective Cp (capability index).
5. Click on the 
button.
- By selecting the Fixed limits option, the Lower control limit (LCL) and Upper control limit (UCL) fields must be filled out.
- In the case of variable characteristics, it is possible to define an objective Cp (capability index) for the system.
- The values will follow the measurement unit initially configured. To learn more, access the Configuring a measurement unit article.
Conclusion
Setting control limits ensures that the process is compliant with the standards and regulations, preventing legal and/or security risks.
To continue configuring the characteristics for the collection, return to the Configuring a characteristic for collection article.