aRotax 914?
Message text written by Fred Fillinger
>Fully agree on 4 probes, as one tells ya' absolutely nuthin. However,
on the Rotax where you can't adjust mixture, all EGT tells you is
impending upper cylinder problems and importantly who's the culprit.
Arguably nice to know, but the Rotax service record is excellent.
Switching 4 EGT probes can degrade accuracy a lot, and 4-probe
displays are very pricey. If one is handy with electronics, all you
need are 4 little LCD 0-200mv display modules ($10-$25 a pop). Plus,
they now sell high-temp thermocouple probes (c. $25) for digital
multimeters that, with aid of a torch, you can calibrate and thus
equalize the 4 modules. The absolute accuracy of any one cyl's
reading is not as important as comparative temps.
<
Having 4 probes can be helpful in other ways too. For instance if you get
an excessive mag drop finding which is the problem plug is just a matter of
cycling through to find the cylinder with the low EGT. I installed 4 probes
and routed the dedicated wires through the firewall before connecting them
to a 4 way selector switch within a small metal box. Keeping the initial
connections aft of the firewall helps to improve accuracy (by preventing
heating of the cold junction of the thermocouple) and the metal box and
screening help to prevent interference. In my case the output feeds into
the uMonitor display. Having just a small switch on the panel helps to
minimise occupation of valuable panel space.
Nigel Charles
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