How should I set the parameters of PID Autotuning such as relay amplitude and PV noise level?

[loghmani]

I want to control the temperature of a room by changing the hot water flow of a radiator with a control valve. The desirable control accuracy is +/- 0.5 degree of centigrade.

What number should I set for relay amplitude? And what number should I set for PV noise level?

[David-A]

Hello loghmani,

Are you using the PID and Fuzzy Logic Toolkit?  If yes, is there a specific example you are looking at?  The Autotuning Smith Predictor.vi in the example finder demonstrates how one would use the PID Autotuning (Tempurature).vi.  You may also want to take a look at some of the examples that address various ways to control tank levels, Simulataion - Tank Level.vi being a relatively simple example.

David A

[loghmani]

Yes, I'm using PID fuzzy logic toolkit. It is a real project not an example. In fact I want to use autotuning for setting PID. I want to know how I should set the parameters of autotuning such as Relay Amplitude, PV noise level, Relay cycles for earning the best result. Is there any relation between desirable accuracy and relay amplitude or PV noise level? I set relay amplitude 1 but during autotuning, control output saturated high or low, should I set relay amplitude lower than 1 or higher?

[David-A]

Hello loghmani,

If your output is saturating try to reduce your relay amplitude and/or reduce the gain K_c of the PID controller before starting the autotuning procedure.  You can find more information about each of the parameters that you've inquired about at this KnowledgeBase article.

I would recommend taking a look at the General Auto PID Simulator.vi example.  You can find this example by doing a search in the example finder or by clicking linked example at the bottom of the detailed help page of the Autotuning PID.vi.

If you haven't looked at the PID user manual that also contains useful information on setting up PID algorithims and Autotuning.

David A