Functional Design of the Control Algorithm

Design for safety includes more than simply the physical components but also the control components. We start by considering the design of the control algorithm. 

The controller algorithm is responsible for processing inputs and feedback, initializing and updating the process model, and using the process model plus other knowledge and inputs to produce control outputs. Each of these is considered in turn. 

The basic function of the algorithm is to implement a feedback control loop, as defined by the controller responsibilities, along with appropriate checks to detect internal or external failures or errors. 

Feedback is critical for safe control. Without feedback, controllers do not know whether their control actions were received and performed properly or whether 

Updating process models requires feedback about the current state of the system and any changes that occur. In a system where rapid response is necessary, timing requirements must be placed on the feedback information that the controller uses to make decisions. In addition, when task performance requires or implies a need for the controller to assess timeliness of information, the feedback should include time and date information. 

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