ndzied1
Lifetime Supporting Member
Here the original spread sheet with actual position rounded to 3 places and control output rounded to 4 places (close but not exactly 16 bit d/a conversion... Actually is about 17.6 bit equivalent).
ndzied1 said:Now a question on the ITAE. You are taking the error (Target-Actual) and multiplying it by the current time. Then you are summing all these values together.
I have no books here to look this up but this just fells fishy. My inkling would be to multiply the current error by the time step and then sum them all up which is how it would be done for crude numerical integration of say a function. Am I missing something here?
ndzied1 said:ITAE:
So in laymans terms, when you multiply the error by the current time, you are saying that an error is worse if it occurs later in the simulation.
Perhaps this works better for step inputs because errors at the beginning are inevitable and are only multiplied by small time numbers. We would hope the control can match the straight line later in the simulation so errors there would be very bad and thus are multiplied by the larger time numbers.
Would you agree?
I'll check out the google search next.
Dazed and... said:I'll first admit (at some risk) to being a student. I am having trouble making the transition from theory to application with PIDs. My overly general question is...How does one produce a model equation for a process? If I am asked to program control of a temp control valve or an exhaust system fan, how do I calculate the needed values? How can I come up with the equation needed?
Thanks in advance for any insight.
Thomas Sullens said:a:=1/time constant. This has units of frequency in radians per second. This is also known as an exponential frequency.
Thomas Sullens said:l:= lambda. -l is the desired location for the three real poles.
Peter what do you mean by 3 real poles and what is radians per second?
1
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s+3
1 1 1
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(s+3) (s+3) (s+3)
Thomas Sullens said:Is there any hope or should I just read??