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Thanks for your comment. You shouldn't take the word "input" literally. What you are referring to is an "actuator hardware fault" which, indeed, may be catastrophic for a control algorithm. What I understand as input "disturbance" is, say, an abstraction/simplification of a wind gust on a drone, opening your fridge's door, opening the faucet to drink water from a level-controlled tank... let me explain: you have a manipulated "actuator input" variable that can exert, say, a force on something you are moving in the direction and magnitude you wish... that's good; however, other guys may also be exerting unexpected/unmodelled forces (wind on a drone, augmented friction on a mechanical system, somebody pushing...) the end result is that the resultant force is not what you think it will be, and the difference is abstracted in the concept of "input disturbance". There is no "hardware fault" in there: on the contrary, your drone control must be there in order to avoid the drone drifting because of air currents and propeller miscalibration. In general, you may be providing a "manipulated, known" amount of "power" or "inflow" to move/heat/charge some system but the resultant power is not 100% what you thought you were providing; no problem because you get informed of that situation with sensing, nothing is wrong/faulty there: if your sensors detect that the drone is moving left when you thought it should remain motionless, your controller will react and push it rightwards just a little, in order to compensate for that "unknown thing", i.e., disturbance that seems to be moving it. No fault is happening in your propellers, it's just the wind. So, "input disturbance" is the "theoretical abstraction" of these issues when we are not interested in the actual "physics" or "technological detail" of what is causing them/how they happen: the most simple way of simulating the above kind of events to validate a PID behaviour is to add, say, a step on the input side, to see how the PID reacts to compensate for it.

@@ASalaControlEN drone: input disturbance: the motors dont go to the rpm set by the controller output disurbance: wind or a push on the drone out of position fridge: input disturbance: the cooling circuit does not give the cooling it is supposed to output disturbance: opening the door level controlled tank (assuming constant flow out of tank, controlled by water being added): input disturbance: the water being added is not what is expected by the controller output disturbance: opening faucet to empty faster or less flow out of the tank input: actuation output: result input disturbance: error on the actuation output disturbance: error on the result

Dear Rezah, Well, it seems that what I call "manipulated input" or "manipulated actuator" you name it, plainly, "input". And "everything else", you name that as "output". Well, if that's what you understand, that's not what I understand... No problem, we have different opinions, but we can live on our lives happily. My opinion in systems-theory jargon: INPUT: anything that can change the "internal state/energy/mass" of the process I am interested in controlling. There are TWO classes of inputs: the "manipulated ones" in which I can decide its value (manipulated actuation) and the "non-manipulated inputs", which come in as they wish and I must counteract. OUTPUT: what my sensors tell me about the internal state/stored energy/stored mass in my process. Then, in "generic systems theory" there is no such thing as "output disturbance". Disturbances may affect internal states in many ways, so we need to discuss controllability, observability, etc. for each input and sensor. Now, terminology in "single-input single-output process control simplifications" of the above general setup: INPUT DISTURBANCE: any "disturbance input" whose effect is (maybe approximately) equal to that of my "manipulated input"... any "external force" to my drone, any "thermal power drain" in my fridge, etc. OUTPUT DISTURBANCE: any "disturbance input" whose effect on my output of interest might be "faster" than that of my actuator, of which affects other subsystems/states different to those that my actuator is able to change, and important for my control tasks (target motion in tracking, measurement noise, ...). If my system is stable, slow input disturbances can be converted to output ones via a block diagram transformation. Fast output disturbances cannot be converted onto input ones. But, as I said, we are not starting a war here... Just note that classifying everything into "either input or output" is a simplification just as naming a color "either black or white"... there are "grey" things.. and in full-fledged system theory there are inputs, states, outputs, and controllable subsets of states for a given input, and observable subsets of states for a given sensor, and quantitative measures of controllability and observability... so there are many terminology nuances which are needed for a correct formal analysis apart from "input" versus "output". Best regards.

@@ASalaControlEN your definition is so complicated 🙂 it was very interesting to read how theorists view things, if anything that affects the internal states is an input disturbance isn't everything an input disturbance? also when you put the disturbance in front of the system in the block diagram, that is the input of the system, which is the actuation signal anyway, we disagree, no war, in the middle east we argue about everything but as long as there is no insults, everyone is friends

" if anything that affects the internal states is an input disturbance isn't everything an input disturbance?" In an abstract sense, yes: disturbances are always "inputs" to a system. The actuation signal is "just one of the possible inputs" affecting the energy/mass balances of my process. Disturbances "added at the input" or "added at the output" of block diagrams are simplifications for a first approach to testing PID control performance. And, yes, you have many more important issues to discuss in middle East than what is the meaning of "input". Best wishes, my friend.

Thanks for the comment! This is part of a case study, with 7 videos planned... But it'll take some time to complete and I have other videos with other topics in publication queue. It's the first one with just a bit of "motivation" towards understanding what might mean in "practice" what we'll do in next videos when devoting a lot of time to theory and simulation with the transfer function 2/s^2. Nevertheless, I'm a theory guy so the forthcoming videos will deal with ode45 simulations, pole placement, Laplace transform manipulations and the like. Actual "motion control" equipment will be for sure better presented in websites and YT channels of commercial companies in the area, I guess. Spoiler: motion control with reducing gears, hydraulics, etc. is better modelled with 1/s (kinematic control) than with 1/s^2 (dynamic control)... Keep tuned !-)

I am not modelling pressure. So, this extremely simplified model is intentionally useless to compute pressure drops and pumping power needs: I am just modelling thermal energy balance under incompressible and constant specific heat assumptions. Regards!

Thank you for the comment. Best, Antonio.

Indeed, you are right, thanks for the comment. Of course, this is a "toy example": a system with a single uncertain real parameter, plus the fact that it is in "open loop", which makes things even simpler. The true reach of uncertainty descriptions in robust control is usually apprehended in closed-loop configurations, also adding some "ultidyn" (uncertain LTI dynamics) with no prescribed order in order to encompass that "unmodelled dynamics" in the uncertainty description, or using small-gain results to probe robustness even in front of sector-bounded nonlinearities... In summary, this video is just a first glance to the idea, oriented to students that were taught what damping and overshoot is, in order to motivate them towards the interest of more ellaborate approaches, Regards!

Thanks for commenting... and, yes, an experienced technician can do many things... and often be faster than an engineer in doing them... but somebody must invent/define what "phase angle" is, and what "spectrum" is before building the first spectrum analyzer, so everybody is needed: someone must know Maxwell equations to pass them to the next generation but he might have no idea on what a "ground wire" in a home is, and vice-versa, a technician can set up your antennae, fiber, grounding, etc. without knowing who were Laplace and Maxwell , and in a much better way than a Physicist!. Thanks God, all flavours of technical knowledge have its role. Regards, A. Sala.

@@ASalaControlEN my fav sinusoidal waves are photons, may I offer these tidbits from the Popcorn Model of Nature's Reality. This is in the study of the Harmonics and the Harmony of Our Universe in the context of Everything: so, lets use a metaphor where 1 musical note, (*) , represents Nature's Reality; This note, (*) , represents the true existence of Nature's reality. This is the realm of the lord, the almighty GOOD (not a religion but an attitude). The real note in which everything resides. What follows are just harmonics of the supreme existence of reality. 1st harmonic of reality (hor)* the human mind and the MotherVerse. 2nd harmonic of reality * commonly referred to as our universe and where electromagnetic radiative force is dominant. 3rd hor * dark matter, the strong nuclear force dominates. 4th hor * the weak nuclear force dominates. 5th hor * gravity, where the popcorn really explodes. 6th hor * time, the here and now where the rubber meets the road. The 3rd, 4th, and 5th combine to create Dark Energy. This not everything. Undescribed harmonics extend, ad infinitum, above and below the note (*). The harmonics show that space that appears empty is never in fact empty. Between Nothing and Everything is Something :)

Thanks for your comment... From me, wannabe nerd, to actual nerd: if you are in particle physics, this is just a toy problem compared to Einstein, Dirac and the like whose intricacies I fail to comprehend. By the way, you've got quite an eclectic/unconventional channel: pride, Socrates, physics... thumbs up!.

@@ASalaControlEN It's quite nice and I taught myself basic electronics when I was 13. It's ALL connected, one way or another.

Glad it helped ;-)

Concise but intense 🙏

@@ASalaControlEN Thank you for your efforts

You are welcome. Thanks for the comment.

I'm glad to be helpful. Thanks for commenting! Just added a link to the `matrix form' video in the description.

You are welcome!

Thanks 🙏 Gracias

Wow... Maybe power off, reboot and underclock your CPU at 0.75X . 😵‍💫