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 rea

son for why anybody should bother with root locus. Why, because root locu

s 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 g

rains. A Ki, Kp, Kd and second derivative gain K2. A system having only on

e gain would be a device like a pressure regulator where the spring provide

s 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 solutio

n 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 thorou

ghly understood because open loop transfer functions are not provided in re

al life like they are in your control theory book. I have NEVER seen a sys

tem with an open loop transfer function provide. I have ALWAYS had to comp

ute that one my own. You can't control what you don't understand unless yo

u are willing to try a lot of trial and error ( tweak gains and drink coffe

e ). Even then you may fail because you don't have the right number of ga

ins or you assume that time constants really are constant. ( sometimes the

y 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 crit

ical 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 mor

e poles that may be real or complex. I will investigate many of these comb

inations. 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 ac

curately than you can calculate them directly from the feed back devices.

Just about anything else your instructors will teach you is useless informa

tion that will just fill your mind with garbage.

So finally, here is my video on why the root locus is useless.