page_title: Control–feedback–abort loop
section_title: Control charts
hierarchical_section_title: Control–feedback–abort loop / Control charts
caption_attribution_description: English: Control Chart showing in-bounds area
context_page_description: Too often systems fail, sometimes leading to significant loss of life, fortunes and confidence in the provider of a product or service. It was determined that a simple and useful tool was needed to help in the analysis of interactions of groups and systems to determine possible unexpected consequences. The tool didn’t need to provide every possible outcome of the interactions but needed to provide a means for analysts and product/service development stakeholders to evaluate the potential risks associated with implementing new functionality in a system. They needed a brainstorming tool to help ascertain if a concept was viable from a business perspective. The control–feedback–abort loop and the analysis diagram is one such tool that has helped organizations analyze their system workflows and workflow exceptions.
  The concept of the Control–Feedback–Abort loop is based upon another concept called the ‘Control – Feedback Loop'. The Control – Feedback Loop has been around for many years and was the key concept in the development of many electronic designs such as Phase-Lock Loops.
context_section_description: Control Charts have a very close relationship to the CFA Loop. Control Charts are used to provide a means of tracking the trend and condition of a specific measured item. The Control Chart (see Figure 9) uses the standard deviation of sampled items to determine whether the item is in-bounds (within acceptable conditions) or out of bounds (outside of acceptable conditions). The +3s is also identified as the Upper Defined-Control Limit or UDL. The -3s is also known as the Lower Defined-Control Limit or LDL.
  Those items that are in bounds are considered to be in control (see Figure 10). They can be the Control element of the CFA Loop.
  Those items that are out of bounds are said to be out of control (see Figure 11). The out of bounds areas can also be identified as the Abort element of the CFA Loop.
  Remember that it was mentioned earlier in this document that the CFA Loop and the Control Chart share the similar functions, the difference is in the use and objectives. We have already seen the Control and Abort similarities.
  Let’s look at a Control Chart (see Figure 12) and compare the information in the Control Chart with the CFA Loop elements.
  The ‘in bounds’ area is our Control element. As long as our data points, sometimes called items, are within the ‘in bounds’ area, we are said to be in control. The data points are the Feedback element. The ‘out of bounds’ areas are the Abort elements. Notice that data point 4 is in the ‘out of bounds’ area, which should lead to control being passed to the Abort element in order to take action to bring the future data points back into control. During the analysis of the system operation using the CFA Loop, the abort mechanism should have been clearly identified so that when the system goes out of bounds during operation, the alternate control should have been activated and the alternate action should be no surprise to the system designers.
  The benefit of using control charts is due to its ability to report dynamic conditions of a system in operation. By data point 2, we should be able to see that if the data follows the trend set by the previous data points, the data will go out of control at some point. This ability to see the trend allows for the chart user to take early action to ensure that the system stays in control or to monitor automated abort processes used to bring the system back into control.
caption: Figure 10 – Control chart in-bounds area
exif: {}