What is the deffernce between feedback and feed forward loop in process control?

I would be so happy if you provide some diagrams or suitable links having diagramsWhat is the deffernce between feedback and feed forward loop in process control?
Feedback is where you are measuring the variable that you are trying to control, and then using that info to control it.





Feedforward is where you measure some other related variable, and then use it to control the control variable.





Best example: Driving.





When you drive you try to maintain a certain distance from the car in front of you. Your eyes ';measure'; that distance and if they notice that the distance is shrinking your brain uses that information to have you slow your car down to get back to the initial distance. Feedback.





Say that you are driving, and the person in front of you uses their brakes. That causes the distance between the two of you to get smaller; so you could measure it with the feedback loop of eyeballing the distance and noticing that they are getting closer to you. Or, if their brake lights are working, you notice that the LIGHTS are on. Which has nothing to do with the distance between the cars, but you know that brake lights ON means that the person in front of you is slowing down. Feedforward.





It all has to do with the relationship between the variable you are trying to control, and the variable you are measuring.