Need help on PID!!! F1 F1 F1 !!!

[wonbinbk]

discrete pid equation

Hi all!
I wanna ask you a question about discrete PID controller.
I have found out this equation:
PID=PID_last + Kp (e-e1) + (1/2)Ki.T(e+e1) + (1/T).Kd (e- 2.e1+e2)
with: PID is the output of the controller.
PID_last is the last PID calculated.
e is the error
e1 is the error last.
e2 is the error "last last"
Kp, Ki, Kd is 3 number.
T is the sampling time.
The problem is the sampling time T. It is small number. But I can calc it (about 100us, uhm... not sure...).
But is it necessary to calculate T. Could we make it equals to zero then we don't need to calculate it.
If you have some experiences in discrete PID controller, would you please help me out ? Thank in advance.

By the way, anybody have the tutorial on using HT-PIC? Please post it here. I am bored with CCS C (PIC comliler).

 

[baskan]

T is constant so just consider in your (probably wrong PID) equation :

PID=PID_last + Kp (e-e1) + KI(e+e1) + KD(e- 2.e1+e2).

 

[wonbinbk]

T is constant so just consider in your (probably wrong PID) equation :

PID=PID_last + Kp (e-e1) + KI(e+e1) + KD(e- 2.e1+e2).

Thanks!
yeah T is contanst. I see you make Ki/2= KI. So the Ki constant is not the Ki in PID controller, right?
I am not sure 100% about my equation. What the error? please help me.
This equation, I caclculated my self. Yes, It is different a little from the PID equation that I found on the web. uhm... Can you help me?

 

[instruite]

This guy has given a nice tutorial on PID
**broken link removed**

Other links you might like to see
http://bestune.50megs.com/typeABC.htm
**broken link removed**

 

[dqhuy]

If you write PID on that equation, PID does not work. PIDs in practical programming is much more different.

 

[instruite]

dqhuy:

If you write PID on that equation, PID does not work. PIDs in practical programming is much more different.

Its not that PID equation doesnot work, all the Digital PID controllers are based on these equations only
the only thing is you required different Gains (Kp, Ki, Kd) for different processes for which there is something call "Tuning of PID controller"
you can find many tutorials for that if you search on google

 

[jatayu]

T is the sampling time. for example, if you read the input every 2seconds, so T =2. if you read the input every 0,5 seconds, T = 0.5. thats why this equation called "discrete" PID.
i think like that