Temp Sensor Controlling?

1

Hello Team,

First time poster here, I am just wanting to understand a little more about how this whole system works before I pull the trigger. I have one main question;

Does the BrewPi use both temp sensors in its code to control the temperature or does it just use one sensor and log the other for the graph?

Can you only use one temp sensor in this system? If so would inside the thermowell or the ambient temp of the fridge be the best one to use?

2

It really depends on your setup. Is this for fermentation inside a fridge? If so you will need a temperature sensor to measure the air temperature within the fridge and another in a thermowell deep inside the beer. You can have other sensors for logging only.

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3

@Dan yes this is inside a fridge. I was more asking from an actual control point of view, does the program/code control off both sensors or does it just use one sensor to control the temp and just log the other sensor for show and tell?

4

Yes it uses both. Fridge temperature sensor is the input for the PID loop that is controlling the beer temperature.

5

To expand on what Dan said:

  • It measures the beer temperature, compares it to the beer setpoint and uses PID to calculate the needed fridge setpoint from that.
  • Two other PIDs (one for heating, one for cooling) manage bring the fridge temperature to the fridge setpoint.

So that means for example that when your beer is fermenting and generating heat:

  • Beer stays at 20 degrees
  • Fridge stays at 15 degrees to offset the heat generated by fermentation. Cooler turns on periodically to manage that.
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6

Thanks @Elco. Since the relays are digital (on or off) is the PID algorithm use some sort of time proportional control?

7

Yes, it uses PWM (pulse width modulation). Not on the Arduino though, only on the Spark.

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