Accurate temperature sensor for industrial freezer

1

Hello all,

I have a request to setup a monitoring temperature sensor for a industrial freezer , that is operating at -17 and -24 Celsius.

I have a Shelly 1PM + Addon with a DS18B20. The temperature sensor was working fine for 2 days, but the the readings are off the chart , occasionally it show -4 Celsius with is unrealistic.

Dos anyone have a recommendation for a temperature sensor that is working in a freezer. I can use also a ESP32 board if needed.

Thank you in advance,

2

Looks like dallas tops out at -55c but it’s functional range is -10c. An rtd or thermocouple operating range is around -200c

3

Hello @Mikefila

Do you recommend me to use a rtd with the GitHub - milesburton/Arduino-Temperature-Control-Library: Arduino Temperature Library and one wire connection?

Regards,

4

I’ve only used thermocouples. I favor esphome for these types of projects. There are components for both types. The max31856 platform is only for k type thermocouples.

5

I soldered an MAX31865 and a 3wire temperature sensor and in my freezer I have the same problems:

at 11:55 the temp is -24.26
image

and then at 1:25 the temp is -14.75

esphome:
  name: temp-sensor
  friendly_name: temp_sensor

esp32:
  board: esp32dev
  framework:
    type: arduino

# Enable logging
logger:

# Enable Home Assistant API
api:
  encryption:
    key: "1234"

ota:
  - platform: esphome
    password: "1234"

esp32_ble_tracker:
  scan_parameters:
    interval: 1100ms
    window: 1100ms
    active: true

bluetooth_proxy:
  active: true
  
wifi:
  ssid: !secret new_wifi_ssid
  password: !secret new_wifi_password
  manual_ip:
    static_ip: 10.10.1.247
    gateway: 10.10.0.1
    subnet: 255.255.254.0

  # Enable fallback hotspot (captive portal) in case wifi connection fails
  ap:
    ssid: "Temp-Sensor Fallback Hotspot"
    password: "1234"

captive_portal:

web_server:
  port: 80

time:
  - platform: sntp
    id: sntp_time
    servers:
      - 0.pool.ntp.org
      - 1.pool.ntp.org
      - 2.pool.ntp.org

spi:
  miso_pin: GPIO19
  mosi_pin: GPIO23
  clk_pin: GPIO18

sensor:
  - platform: max31865
    name: "Living Room Temperature"
    cs_pin: GPIO5
    update_interval: 300s
    reference_resistance: 430 Ω
    rtd_nominal_resistance: 100 Ω
    rtd_wires: 3

I used the code from here

6

In the first post the problem was you were getting -4 when the temperature was actually lower. The unit’s operates in the range of -17 to -24.

The graph you posted shows the temp is ranging from -14 to -24. The problem now is the last spike? The plot seems to show consistent rise in temp as opposed to it jumping up several degrees from one reading to the next. Is it possible someone opened the freezer?

7

Hello,

no, the readings are from 23:00 until 7:00 next day. During the night no one is open the freezer.

I don’t think the freezer loses that much energy in this interval.

Now I ordered:

Adafruit Universal Thermocouple Amplifier MAX31856 Breakout Module
K-Type Thermocouple with Insulated Temperature Resistant Wire and Stainless Steel Tip

I will test with those and let you know.

Thank you