# Ziegler-Nichols Closed Loop Tuning

A

#### Anthony Kerstens

Has anyone ever tried to implement Ziegler-Nichols Closed Loop Tuning for PID loops in PLC logic?

I'm about to try and was wondering if there are any issues I should address.

Anthony Kerstens P.Eng.

M

#### Mohan

Should be no problem. Just make sure that your PID, while tunning, is not limited in either direction and in addition to integral time and derivative your feed forward is also set to zero.
In addition note that different PLC's have different units for the integral time i.e. Seconds, repeat/second. etc.

Good luck

B

#### Bruce Durdle

Anthony,
Check the algorithm - the standard rules may not apply if the "non-interactive" version is implemented.

Bruce.

D

#### David Bergeron

Also remember that Ziegler-Nichols tuning values will result in quarter wave decay step response. This response means that you will get a closed loop step response that has decaying oscillating wave overshoot such that the amplitude of each wave is 1/4 the amplitude of the previous wave. This type of response is often too aggressive for many industrial processes.

David Bergeron, P.E.
Thompson Equipment Co.
125 Industrial Ave
New Orleans, LA 70121
http://www.thompson-equipment.comPhone: 504-833-6381
Fax: 504-831-4664
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J

#### Johan Bengtsson

When you do the tuning make sure you make SMALL oscillations. If either of the process value or the output value reaches any limitation your oscillation is too big and you need to lower the gain (otherwise you get parameters beeing too close to unstable). It is better if the oscillation is slowly damped than exactly maintained (that exact point is rather hard to find and the work is completely useless as you don't see any significant difference in the end result).

As someone else noted, check how the PID are implemented and what units are used for I and D. Conversion formulas for the parameters exist between different PID implementations if you need them.

/Johan Bengtsson

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