a 5.45 order is generated by a puls with a frequency of 5.45 the running speed. The term "order" refers, to the referring speed (usually the running or driving speed of an installation or plant). Usually, this are even numbers, unless through a combination of gears you have shafts with differents speeds.
An example: a six cilinder 4-stroke engine (one combustion cylce per two revolutions) generates a 3rd order (and harmonics).
Agreed. But I was hinting that maybe it was say 5.5th order, which is a perfectly feasible thing to find on a 6 cylinder internal combustion engine, for example.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
Tmoose, your right, i was thinking in the line of diesels and gearboxes.
In fact, 5.45th order could well be a bearing. I think SKF has a calculator for bearing frequencies on their site.
In automotive NVH problems, you can find something oddball like 5.45-order vibration when the source is e.g. a belt-driven accessory turning some multiple of crankshaft speed.
For example, suppose you had a 5-blade fan driven at 1.09 x crank speed. It could produce a 5.45-order noise.