Do I need to tune my controller?

[alvinalexander]

Hi:)

Just finished my fridge build with the help of a friend and I am currently running a test on a small bucket of water.

Just like other people here i’m not exactly sure how to tell if the controller is behaving appropriately for my setup.

If its not too much to ask I would just like some feedback on my system and if the activity looks normal. The beer temp seems be maintained quite nicely but I have noticed that the heating elemenet is switcing on and of repeatedly every 4 seconds is during heating. Is that normal behavior? Intuitively I would think that heating for a longer continuos period of time is better and more efficient.

Any feedback would be appreciated.

Thanks
Alvin

 {
      "kind": "Pid",
      "name": "beer2fridge",
      "enabled": true,
      "setPoint": {
        "kind": "SetPointSimple",
        "name": "beer1set",
        "value": 20
      },
      "inputSensor": {
        "kind": "TempSensor",
        "name": "beer1",
        "sensor": {
          "kind": "OneWireTempSensor",
          "value": 15.6875,
          "connected": true,
          "address": "281DD6C00700008E",
          "calibrationOffset": 0
        }
      },
      "inputError": -4.3398,
      "Kp": 2,
      "Ti": 7200,
      "Td": 1200,
      "p": 8.6797,
      "i": 0,
      "d": 57.9219,
      "actuatorIsNegative": false,
      "outputActuator": {
        "kind": "ActuatorSetPoint",
        "targetSetPoint": {
          "kind": "SetPointSimple",
          "name": "fridgeset",
          "value": 30
        },
        "targetSensor": {
          "kind": "TempSensor",
          "name": "fridge",
          "sensor": {
            "kind": "OneWireTempSensor",
            "value": 21.5,
            "connected": true,
            "address": "281092C1070000BD",
            "calibrationOffset": 0
          }
        },
        "referenceSetPoint": {
          "kind": "SetPointSimple",
          "name": "beer1set",
          "value": 20
        },
        "output": 10,
        "achieved": 1.5,
        "minimum": -10,
        "maximum": 10
      }
    }
  ]
}

[Elco]

It looks like your cooler has quite direct influence on beer temperature, instead of mostly having effect on air temperature.
Near the end of your chart, you can see that the room temperature is very high, and the fridge is cooling to keep it around 20. The fridge air temp is above beer temp, but the beer temp is not rising.

I think you would benefit from increasing beer to fridge Kp. I hope that will increase the effect of the fridge temperature on the beer.

[alvinalexander]

HI Elco,

Thanks a lot for a prompt reply:)

What do you suggest that i change the beer do fridge Kp to ?

Here is an updated screenshot of the graph. seems like the the negative overshoot?

[Elco]

Yes, if your beer-to-fridge Kp is now 2 (the default), set it to 5.

Also reduce your cooler Kp (multiply by 0.5) and increase the cooler Td (multiply by 2).