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how to adjust the PID (or RID) of the aquastream xt ?

thomassss

Newbie

Beiträge: 3

how to adjust the PID (or RID) of the aquastream xt ?

Dienstag, 2. Juni 2009, 19:46

Hi,
I'm student in a school of engineering and I try to adjust the RID of my aquastream xt for my computer
I would like to ask the question:
What type is the RID : is it (Kr+Ki/p+Kd.p) ? is it Kr,Ki and Kd that we can adjust in the RID ?
and why can't we put Ki=0 and Kd=0 ? (I don't understand why we are limited to 1)

thank you

thomassss

Newbie

Beiträge: 3

Donnerstag, 4. Juni 2009, 14:42

Hi,
Its me again, I can se that nobody anbswered me.
So I wondered: Is Aquacomputer the manufacturer of the pump aquastream or only the retailer ?
And does someone as the mail of the manufacturer of the pump ?
because they isn't any explanation for the PID of the pump aquastream xp anywhere.
I would need to know how the pump is manufactured to adjust it.

thank you

majorblue

Full Member

Beiträge: 59

Freitag, 5. Juni 2009, 08:08

Hello thomassss,

first of all, welcome to the english forum of AC.

The aquastream pump is controlled by a PID-Controller. That means there is a P element (proportional), a I element (integral) and a D element (derivative). So it is a proportional–integral–derivative controller. It doesn't matter what type, a PID-Controler always has three values you can adjust. How do you want to get the ideal vaulues? By trying or with the method of Ziegler-Nichols?
The reason that you can't put Ki=0 and Kd=0 is, that if you put Ki=0 you have a PD-Controler only. A PD-Controller is the very fast controller but he always has an offset. So you never reach the set-point. If you put Kd=0 you have a PI-Controler only. A PI-Controler reaches the set-point without an offset but it is a very slow controler. To combine the advantages of the PD- and PI-Controller it is necessary to put Ki>0 and Kd>0.

Please answer if you have more questions.

Kind regards.
"Man kann nicht immer gewinnen! Wer es aber nicht versucht, hat schon verloren."

thomassss

Newbie

Beiträge: 3

Mittwoch, 10. Juni 2009, 20:32

Hello,
really thank you for your answer, it really help me.
I worked on my problems but I still have some questions:
- the problem is that if you want to identify the laplace-fonction of your system ( stroida method (open loop) ) you have to put ki=0 and kd=0 ( but i think i have understood that ki=1 and kd=1 are a good approximation because we usualy work with values about 100.)

- the other problem is that the PID type can be : R(p) = K[1 + 1/Tip + Tdp] or R(p) = K' + 1/Ti'p + Td'p and so K=K' Ti/K=Ti' KTd=Td' so its different to adjust Ti or Ti' Td or Td'

if we follow the Ziegler-Nichols'method :


The open loop method allows to calculate PID parameters from the process parameters. The procedure:
  • Step 1: Make an open loop plant test (e.g. a step test)
  • Step 2: Determine the process parameters: Process gain, deadtime, time constant (see below: draw a tangent through the
    inflection point and measure L and T as shown. By the way: Today we have better and easier methods).
  • Step 3: Calculate the parameters according to the following formulas:K = time constant / (process gain * deadtime)
    PI: Proportional gain = 0.9 * K, integral time = 3.3 * deadtime
    PID: Proportional gain = 1.2 * K, integral time = 2 * deadtime, derivative time = 0.5 * deadtime


    Process gain = dPV / dOP, deadtime = L, time constant = T



    so we can calculate K, Ti, and Td
    I think that these values are the one that you put in the PID system, but i would apreciate that someone confirm...because i'm not sure
    If anyone has the answer
    thank you

majorblue

Full Member

Beiträge: 59

Montag, 15. Juni 2009, 07:25

Hi thomassss.

You are right with the conclusion, that K, Ti, and Td are the values you can adjust when you use a PID-controler. That's why I wrote that it doesn't matter what PID-controler it is.
You always can only adjust the gain, the integral time and the derivative time. I think for a PID-controler of a pump in a water cooling system, you can use the values calculated in the way you wrote down. You can also use other methods to calculate the parameters of the PID-controler, but you will always get only the three values (the gain, the integral time and the derivative time).

It is up to you with which method you calculate the parameters. The Ziegler-Nichols'method is only one example. Always keep in mind, that the results of all methods for PID-controler are the gain, the integral time and the derivative time. These three values are the parameters for the PID-controler you can adjust.

Kind regards.
"Man kann nicht immer gewinnen! Wer es aber nicht versucht, hat schon verloren."

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