G Series 3-4
Periodic Temperature Variation
is a new form of engine analysis.
Some valve related engine faults
produce a slow periodic variation in
The oscillation rate is on the order
of one cycle every minute or two. This
is just too slow to be identified by
occasional observation of the
temperatures alone. Yet it is very
important to discover this phenomenon
because it may lead to a catastrophic
engine failure. It readily appears in a
slow sampled spectrum analysis.
Temperature samples are collected
once per second for each cylinder and
analyzed each second. The entire sample
interval is about 8 minutes. A normal
indication will be a flat line with a
little noise, while a trouble indication
will show as an obvious spectral peak.