Stupid Question-- Why not Open-loop?

The first thing to realise about a system is where the boundaries are going to be. Until you have defined the boundaries of the system you cannot analyse the system for open or closed loop behaviour. Draw the boundaries in a different place and the whole aspect of the system can be changed.

The message is, draw the boundary appropriately, ensure you specify the boundary conditions properly and be mindful of the limiting conditions of imposing such a boundary.

Sure, Paul, but while that's important for technical analysis, it's not very useful for ordinary discourse. The question of whether a rowboat is an open- or closed-loop device shouldn't even come up.

Jerry

I don't think it was mere quibbling about a definition, and I don't think it was even about the difference between open loop and closed loop. I was trying to give examples that would sound immediately like open loop. It was intended to be about the overlooking of things that are open loop control. I would think there are many examples of open loop control around that people don't think of as 'open loop control', maybe because they hardly think of them as controlled, or maybe because they hardly think of them at all.

According to the discussion that you don't think is quibbling, any intentional corrective (or disruptive!) action isn't open loop because the intender closes the loop. If you buy the quibbles.

Jerry