PMUX

[PJF]

I'm studying ( general ) info on FADEC for an exam and have come across the term PMUX ( performance multiplexer ) in relation to CFM56-5 engines.
Can someone please give me a brief explination of PMUX.

[barit1]

The PMUX I'm familiar with captures N1, N2, EGT etc along with ambient conditions for trend monitoring purposes. I think it was optional equipment, and some customers declined it.

But I know nothing of its use on CFM's.

[ICT_SLB]

PMUX (Propulsion Multiplexer) is just another word for EEC (Electronic Engine Control) - it's, in effect, a single channel FADEC in that it has limited authority to optimize the engine relative to the loads on it (thrust, electrivcal & especially bleeds). For a given engine model it is not optional (at least it wasn't on the early '67s when I worked at the Lazy B). It's other, possibly more important, job is collecting (multiplexing on to the 429 bus) all the engine data (N1, N2, EGT, bleed discretes) for the EICAS - hence the name.

Barit's comment probably came from GE originally didn't think installing the PMUX was required as it would have marginal impact on fuel consumption (at least that was what I was told). The equivalent P&W (Ham-Std) EEC did have a relatively large impact on their engine (3 -5% if memory serves).

[barit1]

My comment was more generic to the early 80's - among other things it assessed the reliability of data gathered from the engine.

You're right in that later, the functions of the early PMUX were absorbed into the FADEC.