What would cause a TEMPer2 USB temperature sensor to 'stick' at certain temperatures?

Question for the temperature sensor experts.

I’ve set up two temperature sensors to run a comparison between my roof space and living areas along with the AIR outside. The two sensors are TEMPer2 USB devices: https://pcsensor.com/usb-thermometer/temper2.html

I’ve noticed that the temperatures reported by the sensors tends to ‘stick’ at particular temperatures as I’ve highlighted in the graph (I’m using the ‘external’ sensors, not the internal ones). What would cause this behaviour?


look at detailed raw data, maybe there are gaps in the data and it just ‘links’ last and newer data points (making a straight line)

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That was my original thought but I’ve confirmed that’s the data being reported by the sensors and it’s being reported at every poll. It’s at the same temperatures that the flat line occurs e.g. 18degC on the red line. The weekly chart below shows this better.

Just to clarify – the data plots with the flatlines are NOT your AIR…is that correct? If so, we can’t investigate your raw data and can only speculate: There must be some weird anomaly in the way your TEMPer2 USB devices collect, interpolate, and report data. It is a bit baffling and when compared to your AIR data does not appear to reflect actual environmental conditions (apologies for the “duh” statement). :nerd_face:

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I will suggest you have defective hardware. Where did you buy them?

Definitely not the AIR, that’s working perfectly.

No doubt that it’s cheap hardware. Possibly faulty. They came from eBay so I’m not surprised at the results. It’s purely out of interest that I’m asking.

I think the sensor is a FM75 low-voltage two-wire. I’ll check the datasheet and see if I’m using them correctly.