I built for logging auditing purposes a simple Temperature & Humidity datalogger, using an DS18B20 temp sensor for sensing an equipment rack and a AM2302 (also know as DHT22) Temperature & Humidity sensor for registering the ambient temperature inside the room.
This setup is running 24 hours a day registering all three sensors values once every minute, then storing the readings in a plain text file for later retrieval, all of this thanks a Python script, called via a cron job every minute.
Graph generation is done via an script using the venerable gnuplot utility.
The device has been running from March 7, but the fact is once a while I got some spikes in the humidity reading, they are no more than a couple of spikes in a single 24 logging day and has been appearing 3 or four times in about 48 days of logging.
The room were the device is running is a small (about 6 square meters) datacenter with no A/C (This is why I put the device in!) and have no AC motors nearby that be causing AC interference, also there is no lights on, also the room is manned a few days a week, the spikes appear whatever the room is manned or not.
Both sensors are connected to the Raspberry Pi by a short cable (about 1.2 meters long); the Temp&Hum sensor cable run straight outside the rack, as you can see in the picture below.
What would be the cause of those random spikes?