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My goal is to have an accurate measurement of the current temperature in my room, which I will use for a thermostat. The problem I have is I bought this breakout board and soldered it to about 5cm long cables and I get too high temperature values (and not only offset, but in a range of about 1.5 degrees Celsius and nonlinear over the range I saw).

Using a laser thermometer I can see that the board is at 22 degC, while the room is at 20 degC. As a host processor I use a Raspberry Pi zero w, which I put a box on top, so it wouldn't distract the measurement.

Is there any reason, why I can't measure the actual room temperature? How is this done in 5$ cheap thermo-stations? They don't have to use extremely long cables or such an extreme isolation, do they?

So the setup looks as follows: I have used a laser thermometer, a cheap thermometer station and the sensor, all measuring right next to each other. If i measure the floor I get good understanding of laser+station, but the sensor breakout board is 1 degC higher than what the other two devices measure.

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  • \$\begingroup\$ You're not turning on the heater, are you? \$\endgroup\$ Mar 2, 2020 at 21:08
  • \$\begingroup\$ The default is off, and I specifically turn it off during initialization, since I had the same thought. Also, when heated I think it should be a much much greater difference, shouldn't it? I just tried it out and yeah - heating really does increase the temperature significantly and very fast. \$\endgroup\$
    – mike
    Mar 2, 2020 at 21:49
  • \$\begingroup\$ @mike Can you answer a few questions I have. (1) You use a laser thermometer to measure a board that measures itself. You gave the laser's results, but not the board's. Why not both readings? (2) You say the room's temperature, but you don't tell me how you measured it. How did you measure it? (3) You have at least two, maybe three, temperature measuring devices. Why don't you see what they each say about an ice bath that has been allowed to stabilize its temperature? (Big icebox, lots of ice, wait an hour or two, then submerge, water-tight where needed, and get measurements. Compare.) \$\endgroup\$
    – jonk
    Mar 2, 2020 at 21:58
  • \$\begingroup\$ I tried to calibratte using ice, but I couln't get that bath to an equilibrium and had unstable measurements throughout the experiment.. \$\endgroup\$
    – mike
    Mar 2, 2020 at 22:36
  • \$\begingroup\$ "... but I couldn't get that bath to an equilibrium ..." Why not? All you've got to do is let the ice melt until it's all floating. Stir it around and you should have 0°C. Am I missing something? \$\endgroup\$
    – Transistor
    Mar 3, 2020 at 0:36

1 Answer 1

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It turns out that with a cable length of about 20cm I am able to get believable results. And I am able to confirm these measurements with a weather station right besides the sensor. It is to 0.05 degC exactly the same. This is what initially I expected these measurements to be.

I will leave this question here for reference for anyone wondering what a huge influence the circuit-board heat can have even with moderately long cables of about 7cm.

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