Simple Examples of Open Loop and Closed Loop Control

I am a teacher in university, and i want to teach students of undergrad level about open loop and close loop control system. Looking for examples from any process industry.
 
We have a casting furnace temperature control system that can be operated in either open loop or closed loop mode.

The temperature of the molten metal is measured with a thermocouple. The reading is visible on a display which also converts the T/C signal to an analog signal that's wired to a temperature controller.

The temperature is affected by (among a host of other things...) furnace power level, how full the furnace is, how far it's tilted, ambient temperature, etc.

In open loop mode, the operators watch the display and adjust the power output level of the furnace power supply to keep the temperature within the desired range. As the furnace empties, they make adjustments to the power level based on experience, trying to "feed forward" what they know the system will need. In this mode, the operators are "closing the loop" to maintain the proper temperature.

In closed loop mode, the temperature controller sends an analog signal to the furnace power supply to adjust its power output. There is a primitive feed-forward that adjusts the gains based on furnace tilt angle. The system isn't always very stable since there are a LOT of other variables.
 
For systems I run in open loop, the output is calculated and I can live with the error. If I can't, feedback is required and I move to closed loop. Once example in power generation is AGC control, where you calculate or measure the site losses (hotel loads) and add to the required generator output to achieve the site NET output. Small errors will be evident (transformer losses, etc.), but in many cases can be considered insignificant. If greater accuracy is required, you feedback from your site revenue meters and move the system to closed loop.
 
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