Tutorial: PID control with SPLat

Welcome to our tutorial on practical PID control using SPLat.

What you will get out of it

The purpose of this material is to help you implement a PID control function within your SPLat controller as simply as possible. I will keep it result-oriented, so the approach will be pragmatic and as non-mathematical as I can make it. Do keep in mind though, that this is a complex subject that people make whole careers out of, and for which there is no clear-cut, definitive set of solutions. At the end of the day it comes down to developing something of a gut feel and maybe even getting a bit lucky!

On the face of it, it may look as if there is an excessive amount of material to plow through here "just" to be able to control something with PID. Trust me on this: It is very easy to get lost in the PID wilderness. Unless you have a lot of prior experience with PID you could save literally days, maybe weeks, by using this systematic, structured PID roadmap and the tools that come with it.

What you will need

To use this material fully you will need:

• The PIDassist program installed in your computer. PIDassist is available free on our website, if you don't already have a CD with it (it may pay to check the website, anyhow, to make sure you have the latest version). When you install PIDassist you also get several SPLat support programs and Excel spreadsheets. You can find PIDAssist in the downloads section of our website.
• A SPLat controller with analog capability. The very best choice in an MMi200DK216 (or MMi99DK216), because I use the LCD display in several programs. Naturally you need it hooked up to a power supply and your computer.
• Access to the process you wish to control. Note: The structure of this material and the procedures set out are suitable only for work on a process that you can fiddle with without doing any damage. They are not suitable for in situ tuning of process plants. So, you can use this if you are developing a temperature controlled biofuel digester, but not if you are controlling an aquarium that's already full of fish.
• Excel or a equivalent spreadsheet program. If you don't have Excel, you can download a free office suite called OpenOffice from www.openoffice.org. This contains a spreadsheet program that will do some of what Excel can do (It doesn't do macros and VBA code like Excel, so you will miss out on some of the functionality).
• The motivation to learn and a willingness to knuckle down and work systematically and studiously through the material.

Skills prerequisites

As a rough guide this material will work best for you if you have the following skills:

• Reasonable proficiency with SPLat programming. You need to have gone past FastTrack and have an understanding of the floating point instructions, subroutines and analog I/O. You should be fully up to speed with the SPLat/PC programming software, and know how to connect to a board, translate and download programs to the board.
• Reasonable proficiency with Excel, including graphing, absolute and relative cell references and block copying and pasting. I make a lot of use of Excel in this material.
• Knowledge of the system, product or process that you wish to control.
• SPLat Controls Pty Ltd

Acknowledgement

My sincerest thanks to my friend Bruce Varley for his constructive inputs to this tutorial. Bruce has been a senior plant engineer in process plants world wide, and has probably forgotten more about PID control than I will ever know. Thanks, mate!

Please note that this material is educational in nature and is not intended as professional advice. It is up to you to apply this material intelligently, to do very extensive testing on any system you create and to seek competent advice where appropriate. You are responsible for the outcomes.