I've built a fairly simple Temperature logging device on an Arduino Mega 2560 R3. I'm using TMP36's, 12 of them in total to log the data. Each sensors VS and GND pins are connected to common rails and each V_out pin is then connected directly to their own analog sensor pin on the Arduino.
The method for logging the temperatures is to record ten successive measurements on one sensor (pausing for 20ms between each measurement) then averaging those ten values, log that value to a data file, then move onto the next pin, repeating until all sensors have recorded a value. Then, wait until 10 seconds has passed and then repeat the process. (doesn't need to be faster since my experiment is hours to days long).
The first image (labeled Sensor 14) is the plot that i'm getting from one of the sensors attached to my heat source, which is about what I'm expecting (X-axis is seconds, Y axis is temperature in Celsius)
On my last test I only needed to needed to log a few locations and I left the rest of the sensors sitting on the desk essentially measuring the ambient temperature, which I'm 90% sure should be constant. However, I logged the data from the sensors anyways and plotted them for giggles and got the following plot (same axes as first)
This image has a pretty clear periodic temperature change, albeit a very small difference. The results I've gotten from this have no effect on my actual analysis, but the source for the periodic signal is what I'm curious about.
I'm no signals analyst, or electrical engineer, I'm wondering if seeing this type of periodic 'noise' indicative of some type of problem with my test rig or if this is fairly normal to see. (The sensor has a listed +- 2 degrees C accuracy with a 0.5 degree C linearity)
And as a second part to the question, would there be anything 'wrong' with removing this periodic signal from my temperature data? (running an fft on the noise signal, identifying the frequency and then using a bandstop filter to clear it out).
Many thanks for any advice!
I made a better plot in python and zoomed in on one section to show how the two signals look over a shorter period of time: