Problem AG4108 SNF 2008-06-13 21:14:48: Temperature Faults

shott at snf.stanford.edu shott at snf.stanford.edu
Sat Aug 2 16:44:15 PDT 2008


Preliminary investigation of this problem:
We got some replacement overtemp snap switches from AllWin.  I mounted some of them on an aluminum block with silicone heat sink compound and then also placed one of the in-use ones (the most readily accessible top plate unit) on the same block.  I then heated the aluminum block on the digital hot plate in litho in 5 deg C increments.  All three switches tripped at an indicated hot plate temperature of 75 degrees C within 1 degree C.  I was surprised how close they were.  The replacement ones seem to indicate a trip point of 150F which is about 65C.
In any event, I think that our premature over temp is NOT a temperature switch problem and is likely indicative of a real cooling problem.
As soon as we can, I would like to place flow meters temporarily in each of the 7 cooling legs that run in parallel to see how the 2-2.5 gal/min cooling flow is divided amongst the 7 paths.
My guess is that it is not terrribly even.
John




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