YM:S7 Controller Optimization

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1 Usage

Quick tips on how to optimize a S7 temperature controller.

Some basic and valuable information can also be found here: ETS132_Controller_Setup_Rules

or here:

Cascade_Controller_Adjustment_Rules

Example Cascade Controller with electrical heating.

As you see the actual air temperature was quite unstable.

The controller output was fluctuating constantly between 0 and 100%.

So the behaviour was more like a P-control instead of a PI control.

Let's optimize with some basic rules.

Initial (horrible settings):

- Kp = 4.0

- Ti = 5sec

First step: Determine the critical kP-value.

Set Ti to zero - so that we have a pure P-control.

Increase Kp until the behaviour gets unstable and over- and undershooting gets bigger.

This value for kP is called critical kP .

Basic Rule: Set 50% of the so found critical kP.

Now we have a look at the cyclic duration - with this we determine the value for Ti.

While working as a pure P-control we check the cyclic duration. We find approx. 10 minutes.

Basic Rule:

Set Ti to 85% of the so found cycle duration - so set this to 510sec in our example.

Now...result:

Looks good. Different to the initial situation our controller output has a quite constant output, which leads to a constant load and therefore to a good temperature behaviour.

The interesting part starts with a setpoint change:

No further optimization necessary.

We made a setpoint jump from 120°C to 200°C and had an overshooting of 0.5°C - this does not get any better. Also the controller output looks really good.