How to correctly use Self Tune FB?
I am haveing a bit of confuse trying to use selftune function block.
I was trying to tune a tempreature loop but it is quite a bit tricky. the loop is for controlling condensation ratio of chemical processing factory.
The first loop is for jacket and internal of the vessle. it can be tuned with ease, however the loop that control condensation is quite hard to tune. First i must wait for the first two loop to reach steady state. When condensation start, the condensor loop will have to try to keep a steady tempreature for the process to have consistancy.
The condensation process mean that the loop before condensor will loose quite a bit of heat and will render the loop of jacket to start oscilating. When the jacket of this vessle oscilate it also cause the condensor loop to oscilate.
How Do I use the sefltune function block correctly?
Are there a standard steps to follow?
Voted best answer
If the loop is "hard" to tune then it is unlikely that any Auto-tune algorithm is going to be able to tune this for you. Basically, Auto tuners need to be able to get clear repeatable results from a bump test on a process with no disturbances. If you cant get this manually, then there is very little that the auto-tuner can do any differently.
You need to identify why this looop is "hard". Is the loop stable in manual ? Is the equipment properly serviced and installed ? Has the control loop been designed properly? Is deadtime excessive? ( and it sounds like the answer to this question is "yes". Many self-tuning algorithms cannot handle this properly at all) Is the gain non-linear ( ie it changes as the process changes) is the process "symetrical" ( ie the gain for an increasing process should be equal to the gain for a decreasing process)
You should be able to find some usefull information here -> http://tinyurl.com/kcda75v
Not familiar verymuch with your process requirement, but if you want to control ratio then use C_CR block(Continuous controller, ratio)!
Also it's sensitive playing with loop in realtime, try with your setting on emulator and then implement in realtime.
I saw your previous question, too. try with default values mentioned in manul of self tune block.
CP = 0.5 (Proportional Correction Value)
CD = 1.0 (Derivative action)
TR = 15 sec 00:15.000(reset time) integral time.
TD = 0 sec (rate time) derivative time.
I recommend first to go through detail of C_CU and selftune blocks it is explained very well in help file. and alternatively try with C_CU block and emphasis on 2/3 parameters settings to control your loop
Hope that helps!