Hey guys, wondering if you could give me some direction with PID tuning. This is my first real attempt at tuning so please bare with me. I've read a lot about PID tuning and the concepts, I'm now trying to put that knowledge to use!
I've attached a graph of my SP, PV, CV values over a 3 hour period of time. I'm controlling the temp of an oven using the PID function of a Controllogix 1756-L62.
PID is Dependent, triggered every 1 sec, loop update 1 sec.
SP-PV
Derivative of PV
Kc = 3
Ti = 3
Td = 0
I used the WAG method to get to these PID values based on the data I've collected during previous test runs.
The response of the system to a set point change isn't that important, stabilization is. Process limits of +/- .5 deg C needs to be maintained through the process (SP does not change during a process run).
As you can see by my graph, I've got some overshoot and undershoot of PV going on but the integral squashes that pretty quickly. After about 25 min it stabilizes (would be great to get this under 20 min, but again not that critical).
As is, it will achieve what we need, but I'd like to fine tune it to eliminate the overshoot, and to just gain experience.
Looking at my graph, what tips you off? I see my CV oscillate a little after the initial ramp, which tells me it could be improved. Do I need more gain, less gain, more integral, less integral...by looking at the graph what stands out that tips you off (besides the overshoot)? What do you see that indicates P or the I or the D need to be changed?
My thoughts by looking at the graph:
Kc: Possibly lower a little to stretch out the initial ramp
Ti: No change
Td: Add in to eliminate the overshoot but I have no clue where to start for a value.....
Hopefully this is a good example…
SP steps are 105, 75, 105
I've attached a graph of my SP, PV, CV values over a 3 hour period of time. I'm controlling the temp of an oven using the PID function of a Controllogix 1756-L62.
PID is Dependent, triggered every 1 sec, loop update 1 sec.
SP-PV
Derivative of PV
Kc = 3
Ti = 3
Td = 0
I used the WAG method to get to these PID values based on the data I've collected during previous test runs.
The response of the system to a set point change isn't that important, stabilization is. Process limits of +/- .5 deg C needs to be maintained through the process (SP does not change during a process run).
As you can see by my graph, I've got some overshoot and undershoot of PV going on but the integral squashes that pretty quickly. After about 25 min it stabilizes (would be great to get this under 20 min, but again not that critical).
As is, it will achieve what we need, but I'd like to fine tune it to eliminate the overshoot, and to just gain experience.
Looking at my graph, what tips you off? I see my CV oscillate a little after the initial ramp, which tells me it could be improved. Do I need more gain, less gain, more integral, less integral...by looking at the graph what stands out that tips you off (besides the overshoot)? What do you see that indicates P or the I or the D need to be changed?
My thoughts by looking at the graph:
Kc: Possibly lower a little to stretch out the initial ramp
Ti: No change
Td: Add in to eliminate the overshoot but I have no clue where to start for a value.....
Hopefully this is a good example…
SP steps are 105, 75, 105