• #### Learning Root Locus is Useless ( well almost, but I have never used it.

From pnachtwey@gmail.com@21:1/5 to All on Sat Aug 20 19:10:56 2016
My videos will concentrate on what people need to know using the tools taht are available today. I despise the propagation of old techniques like Z-N. They are a waste of time and misleading. So is Root Locus. I like to start out any topic with the
question "Why Bother". I can't find a good reason for why anybody should bother with root locus. Why, because root locus deals with how the closed loop poles will move with just one proportional gain. That isn't reality anymore folks. It hasn't been
since the dawn of micro controllers. In many of the systems I get involved in there are 4 grains. A Ki, Kp, Kd and second derivative gain K2. A system having only one gain would be a device like a pressure regulator where the spring provides the
proportional gain.

I used an example transfer function that another YouTuber/professor used in his video. He goes through all the BS of finding the break away point and where the closed loop poles are purely imaginary but he provides NO solution that will result in a
decent closed loop response.

In my videos I will stress 3 things.
1. System identification. This should be the first topic taught and thoroughly understood because open loop transfer functions are not provided in real life like they are in your control theory book. I have NEVER seen a system with an open loop
transfer function provide. I have ALWAYS had to compute that one my own. You can't control what you don't understand unless you are willing to try a lot of trial and error ( tweak gains and drink coffee ). Even then you may fail because you don't
have the right number of gains or you assume that time constants really are constant. ( sometimes they aren't)

2. Pole placement.
There is the mathematical definition of poles that you can read else where but how do they manifest themselves in a real system. Basically, poles are caused by things that store energy. Knowing where the energy goes is critical for a gut feel but the
pole placement allows one to control the system accurately.
There are integrating and non-integrating systems that have one, two or more poles that may be real or complex. I will investigate many of these combinations. All these different types of open loop systems require different techniques to control
properly.

3. Observer or model based control
There is no way you can do this without getting past step one but once you do you can estimate the process value, PV, and its derivatives much more accurately than you can calculate them directly from the feed back devices.

Just about anything else your instructors will teach you is useless information that will just fill your mind with garbage.

So finally, here is my video on why the root locus is useless. https://youtu.be/uYhz3TuTkfM

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