Temperature stability for a Proofing oven

ESPHome
1

Im looking to modify a oven and use the bottom element switched with a relay controlled by a ESP32 for a temperature stability of around 26°C (78°F)

Ive fitted a thermocouple into the oven but have found the temperature readings to be unstable, I need to have quite a quick response due to transfer coefficient of the heating element (about 6A) -

Sample of temp readings over an hour

Screenshot 2024-01-20 at 11.43.20 am
Screenshot 2024-01-20 at 11.43.20 am2396×856 143 KB

The oven wasn’t on during this measurement, its just showing the ambient temperature.

Is there a way to stable this or a better sensor for the job.

The code I’m using -

ESPHome code for thermocouple 
spi:
  miso_pin: 12
  clk_pin: 14

sensor:
  - platform: max6675
    name: "Oven Temperature"
    cs_pin: 15
    id: oven_temp
    update_interval: 30s

I then plan to use a ‘Bang Bang’ or Thermostat controller PID for the relay switching but the issue is getting a stable reading first. Any thoughts would be appreciated.

2

Seems like you maybe have a bad sensor or amplifier (or bad wiring), because if the temperature is actually stable, you shouldn’t be getting that much noise. I’ve used a thermocouple with that same amp and there’s no noise in my readings.

Are your thermocouple wires soldered to the amp or are you maybe using a breadboard?

3

Thank you, they are clamped with the existing folk terminals and a 0.01uF cap across them (the cap made no difference but left it there).

4

A thermocouple seems a bit of overkill for a proofing oven. Isn’t 26 degrees right at the bottom of the range for something that can typically read to over 1000 degrees?

In my proofing cabinet I use a good quality DS18B20, it’s extremely stable and responsive. Temperature range of the cabinet varies about 1.5 degrees around the set temperature once it gets running.

5

Yes your right but I’m working on a project to modify our own oven meaning when its not proofing, its baking at around 260C and then the poor little DS18B20 would melt.

If it doesn’t work out, I might end up using the DS on a unit I can place in the oven just for proofing and remove for baking but would prefer a fix device.

When the proofing control is off, i.e. when the ovens baking, the relay on the bottom element would reconnect the oven to work as normal as the relay would be in its resting state, that’s the aim.