This might seem like a dumb question however I can't see the difference and can't test it as I don't have an allen bradley PLC available.
In the PIDE block the function is CV = CV-1 + Kp* Delta E + ...
How is the action of the proportional gain any different to the derivative in this case? Eg Kp * Delta E vs Kd * (E -2En-2 + En-1)
Eg the following values:
SP: 50
PV: 50
CV : 0
KP = 1
KI = 0
KD = 0
Change PV to 75 with a Kp of 1 and scan time of 1 second
Delta E is 25 hence CV = 0 + 1*25 so CV = 25
OR
SP: 50
PV: 50
CV : 0
KP = 0
KI = 0
KD = 1
Change PV to to 75
CV = 0 + 0*25 + 1*(25 - 0 + 0 )/ 1 so CV = 25
if you use the traditional equation of CV = KP * E then the proportional gain operates quite differently to the derivative, however if you use change in PV as your proportional gain entry in a PIDE block I'm curious how this acts any differently to derivative gain?
Can someone explain where I am going wrong? The reason I ask this question is I have the following example in the field where the PIDE simply does not work.
SP: 10000
PV: 1000
CV : 0
in 1 second PV jumps from 1000-3000, so a delta E of 2000, even with a tiny Kp this results in movement of the CV despite the PV being absolutely no where near the SP. I would expect this behaviour from Kd however there seems no way to avoid it when using a PIDE block.
The solution is to use a PI block instead however it raised the question of how is Kp different from Kd in a PIDE block?
In the PIDE block the function is CV = CV-1 + Kp* Delta E + ...
How is the action of the proportional gain any different to the derivative in this case? Eg Kp * Delta E vs Kd * (E -2En-2 + En-1)
Eg the following values:
SP: 50
PV: 50
CV : 0
KP = 1
KI = 0
KD = 0
Change PV to 75 with a Kp of 1 and scan time of 1 second
Delta E is 25 hence CV = 0 + 1*25 so CV = 25
OR
SP: 50
PV: 50
CV : 0
KP = 0
KI = 0
KD = 1
Change PV to to 75
CV = 0 + 0*25 + 1*(25 - 0 + 0 )/ 1 so CV = 25
if you use the traditional equation of CV = KP * E then the proportional gain operates quite differently to the derivative, however if you use change in PV as your proportional gain entry in a PIDE block I'm curious how this acts any differently to derivative gain?
Can someone explain where I am going wrong? The reason I ask this question is I have the following example in the field where the PIDE simply does not work.
SP: 10000
PV: 1000
CV : 0
in 1 second PV jumps from 1000-3000, so a delta E of 2000, even with a tiny Kp this results in movement of the CV despite the PV being absolutely no where near the SP. I would expect this behaviour from Kd however there seems no way to avoid it when using a PIDE block.
The solution is to use a PI block instead however it raised the question of how is Kp different from Kd in a PIDE block?