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Andrew de Quincey 2021-04-30 22:59:55 +01:00
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docs/ziegler_tuning.md
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@ -4,17 +4,18 @@ This uses the Ziegler Nicols method to estimate values for the Kp/Ki/Kd PID cont
The method implemented here is taken from ["Ziegler–Nichols Tuning Method"](https://www.ias.ac.in/article/fulltext/reso/025/10/1385-1397) by Vishakha Vijay Patel The method implemented here is taken from ["Ziegler–Nichols Tuning Method"](https://www.ias.ac.in/article/fulltext/reso/025/10/1385-1397) by Vishakha Vijay Patel
One issue with Ziegler Nicols is that is a **heuristic**: it generally works quite well, but it might not be the optimal values. Further fiddling may be necessary. One issue with Ziegler Nicols is that is a **heuristic**: it generally works quite well, but it might not be the optimal values. Further manual adjustment may be necessary.
## Process Overview ## Process Overview
1. First of all, you will record a temperature profile for your kiln. 1. First of all, you will record a temperature profile for your kiln.
2. Next, we use those figures to estimate the parameters. 2. Next, we use those figures to estimate Kp/Ki/Kd.
## Step 1: Record Temperature Profie ## Step 1: Record Temperature Profie
This must be done without any interference from the real PID control loop. To do so, run: Ensure `kiln-controller` is **stopped** during profile recording: The profile must be recorded without any interference from the actual PID control loop (you also don't want two things changing the same GPIOs at the same time!)
To record the profile, run:
``` ```
python kiln-tuner.py ziegler.csv python kiln-tuner.py ziegler.csv
``` ```
@ -42,7 +43,7 @@ The values will be output to stdout, for example:
``` ```
Kp: 3.853985144980333 1/Ki: 87.78173053095107 Kd: 325.9599328488931 Kp: 3.853985144980333 1/Ki: 87.78173053095107 Kd: 325.9599328488931
``` ```
(Note that the Ki value is already inverted ready for use in config.py) (Note that the Ki value is already inverted ready for use in config)
------ ------
@ -53,12 +54,13 @@ If you run
python zieglernicols.py zn.csv --showplot python zieglernicols.py zn.csv --showplot
``` ```
It will display a plot of the parameters. It should look simular to this ![kiln-tuner-example.png](kiln-tuner-example.png) It will display a plot of the parameters. It should look simular to this ![kiln-tuner-example.png](kiln-tuner-example.png).
(Note: you will need python's `pyplot` installed for this to work.)
Note: you will need python's `pyplot` installed for this to work.
The smooth linear part of the chart is very important. If it is too short, try increasing the target temperature (see later). The smooth linear part of the chart is very important. If it is too short, try increasing the target temperature (see later).
Note the red diagonal line: this **must** follow the smooth part of your chart closely. The red diagonal line: this **must** follow the smooth part of your chart closely.
## My diagonal line isn't right ## My diagonal line isn't right