I discovered from various sources that the temperature inputs of the Cerbo GX utilise LM335 sensors. I bought a few and before hooking up to my Cerbo (which is 2hrs from home) I hooked them up to a supply, through a resistor to limit the current to 1mA and connected a meter to the output.
the output is meant to be linear with temperature and the spec sheet says that if you calibrate it against a known source at 25 degrees it will be accurate within 1 degree over the measurement range of -55 to 100 degrees So I added a 10 potentiometer to the circuit connected to the adj pin and set it correct at 25 degrees.
My experience is different. At 70 degrees it is 5 degrees out.
There is a suggestion that calibration errors can be accounted for on the Serbo as long as you are logged in as a super user. I see the settings for “offset” and “scale”. Offset is obvious enough, but what is scale? Its default setting is 1.0.
I may be able to get the sensor to read more accurately over my desired range using these settings, but I don’t understand why the sensor output isn’t linear as it is meant to be. Anyone else seen this anomal?
