PLC Programming for Beginners

Hey, another ChemE...

Some misconception here. Matlab was used in class to show you how a PID block is constructed from scratch; it allow to you how theory turns to actual process control in reality. RSLogix is a programming tool for Allen Bradley Branded PLCs. Each PLC or DCS have their own programming software, it's fun to learn them but keep in mind they are just a tool you learn, much like using IPhone vs Blackberry. Just having RSLogix in your resume is not going to get yourself hired as a process control engineer.

In your position, I would ask your boss or coworker to take on process control projects and learn from the controls guy in your facility. We are the sort that like to what little knowledge to young ones. Good luck.

Unfortunately RsEmulate does not support the "PID" instruction.

See links below for some control stuff.

http://www.controlguru.com/

Scroll down and look for "What is P,I and D"

http://www.ronbeaufort.com/sample_lessons.htm

http://www.plctalk.net/qanda/showthread.php?t=62217

Welcome to the forum and congratulations on your degree. I believe controls engineering is probably the most multidisciplinary engineering field you can find (think chemical [for fluid processing industries], mechanical [for machine control], software, systems, electrical, instruments, human factors,...). So, be prepared to continue learning.

Some advice: even though you've made a great investment in the attainment of your degree, do not stop investing in your education even if it's your money. This can be as simple as buying textbooks or actively seeking solid mentors. For textbooks, look for some of Greg Shinskey's books and Thomas Fisher's 'Batch Control Systems' to get you started; buy used.

If you can, choose opportunities that provide the prospect for the most experience and responsibility over the ones that may provide the highest intitial $.

It's been over 25 years since I got my degrees. It would seem many Chemical Engineering curricula still teach controls from a perspective that is nearly worthless from the applied industrial perspective, particularly for fluid process systems.

Good luck and have fun with it.

-Harry-
Thanks for the info. My boss is actually aware that I would like to cross-train for the Process Control group at work. Unfortunately I won't be able to do this soon since they have me working the graveyard shift (10pm-7am). I'm looking to be under this schedule until November of this year, thus the reason of why I am looking for a book that will guide me through RSLogix. And you're right, just because I will be able to one day add RSLogix to my Resume won't mean that I am guaranteed a job, BUT it will definitely distinguish me from everyone else that does not have this experience.

-Mickey-
Thanks so much for those links! They seem very promising!

-James-
You're absolutely correct. As a matter of fact, I love learning! When I took Process Control as an undergrad, I was not able to grasp the concepts like I should have and the reason is because throughout my entire college career I had to work 50+ hours a week in order to pay for my school (and am so glad to say that when I walked on stage, I was walking debt free!) So because I did not learn Process Control the way I wanted to, I grabbed myself a process control book from Pao Chau and I have been re-teaching myself the course all over again. Unfortunately a professor at MIT told me that Pao Chau's book was not the way to go, thus he directed me to purchasing Bequette's Process Control book instead. Both books, Chau and Bequette, rely on Matlab's Simulink for their problem solving. I will look into buying the two books you mentioned.
About the process control material that is taught in college, you're absolutely right. It's basically pointless. I've also realized that in order to understand process control, one must understand how instruments (i.e. regulators, actuators, thermocouples, etc) work. In order to understand how their I/O works, one must have a knowledge of electrical topics since these instruments take voltage or current inputs in order to output a pressure or temperature value that the operator can understand. My coworker from the Process Control dept at work was telling me that back in the days (whenever this was) ChemE curricula included electrical courses. I really think we should go back to this old curricula for ChemEs because clearly we're being cheated at school. I certainly do have a lot to learn because I can fully comprehend how to tune instruments in the real world.
Also, I was shocked to find out that PID tuning is basically a trial and error procedure. I always expected engineers to use methods such as Cohen-Coon and Ziegler-Nichols to find the proper tuning parameters but it looks like these methods take a long time and industries do not have sufficient free time to perform this. But I still think that trial and error also takes a long time (as was the case when we tried to tune the E/P transducer)

It's true that a lot of what you learned doesn't apply, however, for a few select folks, doing complex control is their calling and the stuff you did learn in Process Control does play a role. Just take a look at some of Peter's posting:

http://www.plctalk.net/qanda/showthread.php?t=9768&page=2

http://plctalk.net/qanda/showthread.php?p=408875

http://www.plctalk.net/qanda//showthread.php?t=26395

www.controlguru.com also have good info from theory to practice.

The problem is that unless you work such problems often, you lose it.

As for PLC, another option for you is to get a cheap SLC or micrologix processor on eBay with one or two I/O card. Should run you for less than $500. However, you still need the software but you may ask to borrow the programing laptop from work during the weekend.

Process control can be a lot of fun and challenging. Finding the optimal control strategy can be as difficult as finding the optimal tuning parameter settings. Different processes and different systems may require varying strategies. Sometimes PID's just don't get it done. As for Z-N, I think you will find that it is a bit of trial and error too as you adjust the tuning parameter settings to find the first point of oscillation.

Anyway, getting an old PLC to practice also requires you to get a process to control. Perhaps, you can get a used proportional water valve that you can hook up with a garden hose, get a level sensor of some type that would fit in a bucket or barrel, and get an old PLC with an analog output that you can control the valve. Then you can play all sorts of games with the PID function (and other technics such as error squared). You can try to optimize level control by going to set point as quick as possible. You can learn about dead time. You can use the valve to control the exit of water from the bucket then you can practice controlling the level by metering the removal of water. Then you can practice shocking the system by dumping a bunch of water into the bucket and work on optimizing your control algorithm. Anyway, you really should create a process to control and then tinker with it.

-Harryting-
You're absolutely right. I will keep pushing buttons to see if my boss could grant me the opportunity to cross-train for the process control dept at work.
Also, thanks for the links!
Could you clear something up for me:
Let's take a pressure transmitter. Say we want to maintain a certain clean air set point of 10 psi for our process. I want to understand the electrical aspect of how this "10" arises, how the pulsations detected by the pressure transmitter get converted to a reading that the operator can comprehend. I know this much: the pressure transmitter requires either a voltage or current input, and would convert this input to a pressure reading? I'm just confused by how this happens.

-kb9ttx-
Thanks for the idea! but wouldn't I need instrument air in order to "open" and "close" my control valve?

Learning about the hardware is part of the learning process and the answer is "maybe, perhaps, sometimes, etc."