[evlatests] Mystery temperature swings

[Kevin Ryan]

The WIDAR Prototype Correlator (PTC) is in a half-height rack sitting  
in a corner in the outer screen room in the old VLA correlator room.   
It contains 5 boards each with 5 or 6 temperature sensors.  While  
developing software to monitor these temperatures, I've noticed a  
weird oscillation that occurs for a ~ 2-hour period roughly centered  
around midnight local time.  I've asked Ray Ferraro and Bob Broilo  
about it but they did not know of anything that would cause it other  
than that Ray stated that the temperature in that corner is affected  
by the doors opening and closing.

So now I'm asking more people for ideas.  A graph of the temps on one  
board (they are all similar) over the last two days can be seen here:
http://www.aoc.nrao.edu/asg/widar/temps/mystery-ptc-temps.jpg

The swings from normal daily activity are apparent starting around  
0600 - presumably from the door opening and closing and use of the  
boards for testing - but what about those oscillations around midnight?

It is certainly possible that this is not being caused by ambient  
temperature swings at all; like something going on on the boards  
themselves or possibly even the data gathering system itself.  Can we  
place a recorder near the PTC to monitor its ambient temperature for  
24-hours?

Kevin