Command law
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) | |