When process identification has been done, the controller command law is choosen from the following criteria:

**θ/τ**for stable process, also said with a proportional response,**K×τ**for unstable process, also said with integral response.

Command law for stable process, proportional response Process: Gs static gain, τ pure lag, θ first order time constant, calculate θ/τ |
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θ/τ max | θ/τ min |
Command law |

>20 | Switch (open/close) | |

20 | 10 | P |

10 | 5 | PI |

5 | 2 | PID |

<2 | Closed loop insufficient |

Command law for unstable process, integral response Proces: K static gain, τ pure lag, calculate K×τ |
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K×τ max | K×τ min |
Command law |

>0.5 | Closed loop insufficient | |

0.2 | 0.5 | PID |

0.1 | 0.2 | PI |

0.05 | 0.1 | P |

<0.05 | Switch (open/close) |