https://www.youtube.com/watch?v=T3jBxgzMeLY
When to Use Each Response of PID in BAS Part 6 – Building Automation Systems Training
Welcome to building controls part 6 when to use each response this is the sixth course in the building controls series if you have not already done so please participate in building controls one through five prior to taking this course.
At the completion of this course you will be able to understand how tuning the three terms in a PID response adjust the control for particular needs explain why floating response is more appropriate for fast responding systems and will be able to identify specific uses for each type of response buildings vary widely in the needs that are placed upon control loops to provide comfort to the occupants in an efficient way.
The control loops must be well designed to meet those needs in the previous class we said that a slow responding system would be best fit with a proportional response in this case proportional response is the simplest and gives good stability as well as reasonable offset so how much offset is reasonable well that’s defined by the needs in some cases plus or minus one degree is completely fine.
However in some projects there is a need for plus or minus one tenth of a degree if the system is stable with offset that means it has stabilized at a certain temperature above the set point as long as it stabilizes with tolerable offset.
That’s okay if it stabilizes with too much offset more work would be needed tosatisfy the requirements but why does the system stabilize with an offset why doesn’t it stabilize at the setpoint. It has to do with how the system is tuned.
Let’s see how tuning adjusts the response for different conditions these ideas may be difficult to grasp at first however if you study them and also continue to the next class in the series which has some useful
examples you should readily master these concepts.
A system is tuned to best respond to a certain load condition in the next class we will see this quite clearly with an interactive simulation but for now let’s use an analogy imagine a small puppy the owner can easily control him because she has more strength than he does however if the puppy grows into a big dog he will now match his owner in strength if the owner opposes him to control him.
She will be at a standstill now think of the owner as the system and think of the puppy or the dog as the load on the system.
Let’s summarize some of the information that we have learned in this course today we learn that a system is tuned to best respond to a certain load condition a slow responding system would be best fit with a proportional response.
We discussed why it is beneficial to add the I term to the P what P I responses will give us for moderate responses is the ability to decrease the gain for stability what is gained when you change the gain.
You are changing what the step is up and down for every temperature change we also learned that a derivative term can be beneficial when there are set point changes the term would detect a rapid change in temperature and moderate the reaction from the integral term an alternative is to change set points gradually over time next.
We saw that a floating control is more appropriate for fast responding systems because the dead band helps prevent a controller overworking by adjusting to every change lastly we also looked at a practical example of where each control loop response might be used in our next course you’ll be presented with an interactive illustration of the PID response.