Unmutable alarms and EGT curiosities

[lrg775]

Hokay so, the other day an EGT probe wire failed in flight. The value started dancing around, then going off-scale high and low repeatedly. I now have two issues to bring up:

Every time the failed EGT cycled, it set off a master warning and and EXHAUST GAS TEMPERATURE audible warning (repeating some 1545 times). I could do nothing in flight to shut it up and am 600% regretting following the instruction manual to wire the Dynon audio output to the unmuted input on my audio panel. There absolutely needs to be a way to easily inhibit audio alarms. My GRT Mini-X allows for this, and it doesn't even have alarms worth paying attention to.

Second, I've unplugged (and capped the wires to) the failed EGT probe. Yet somehow, it makes up its own values to track the other EGTs:

At high power settings, it'll read as high as 310 degrees. What gives? Is this some kind of software filtering?

Thanks for looking!

 

[GlennB]

This again raises an old feature request of mine: a softkey selection where a nuisance warning can be silenced, never to return till the next reboot. (Airbus calls it "emergency cancel".) In my case it was a failing oil pressure sender which started reading off-scale high, but the result was the same - a recurring warning which served only as a distraction. So far I haven't been able to convince Dynon of the value of such an inhibit function, though I live in hope!

I've had similar EGT failure modes to yours. The fix, at least until you can replace the probe, is to go into the setup menus and disable the EMS input for that channel. That will take the errant EGT off the screen, along with any associated warning messages, while leaving other alerts functional.

 

[lrg775]

Thanks GlennB - I ended up editing the setup file to disable the alarm on that EGT channel.

I'm still pretty concerned with the make believe EGT values though--has anyone calibrated their EGT probes directly? I'm predominantly wondering if this is some kind of voltage transient or if SV is applying some fuzzing to all the channels.

As for being able to mute the alarms, I'm considering moving the Dynon audio to a switched input on my audio panel...curious if anyone on the forum has solved this in a similar manner.

 

[jdubner]

... a softkey selection where a nuisance warning can be silenced, never to return till the next reboot ...

This. Either a softkey as GlennB suggests or an additional alarm type to complement the SELF-CLEAR and LATCHING types (page 7-79 of the Skyview Installation Manual).

And like GlennB I enter the Setup Menu and disable that particular alarm. But that's a lot of button pressing and head down time for something that happens often such as when a fuel tank gets borderline low in the traffic pattern.

And Irg775, the Dynon EGT probes have been notorious for their short lives. In one of my airplanes, I've replaced every single one of them one or two times in 650 hours. YMMV.

--
Joe
RV-8A / Long-EZ

 

[Stevec]

The unusual values when you disconnect an egt probe are interesting. I was fault finding an egt probe problem the other day. When we disconnected the faulty probe we had a red X on that egt display. We decided to swap with the #1 egt and found when we disconnected that one the temperature displayed on #1 went up to 90 degrees C not a red X as we were expecting. The results were consistent.

 

[swatson999]

when a fuel tank gets borderline low in the traffic pattern.

Fuel level alarms are latching in my setup.

Re: EGT probes...I don't think it's the *probe* that is failing so often for everyone, as much as the *connector*. I replaced all of my EGT and CHT probes with those Omega couplers designed for thermocouple wires, and have had zero problems after several hundred hours now (knock on wood!).

 

[GlennB]

I’m guessing that the input on the Skyview floats to some random value when nothing is connected to it.

The usual failure mode on my Dynon probes was to start flicking to a ridiculously high number, shortly before quitting entirely. The fault was in each case an internal break of the very fine wire emerging from the probe. I switched to an aftermarket brand, and never looked back!

FWIW I’m of the belief that no alarm needs to be set for high EGT, as there‘s no published limit apart from TIT on a turbocharger.

 

[jakej]

Joe, you wrote -
"And Irg775, the Dynon EGT probes have been notorious for their short lives. In one of my airplanes, I've replaced every single one of them one or two times in 650 hours. YMMV."

I understand your pain however the Dynon probes do not have short lives in my experience as I've only replaced 2 of them in the 50 RV's I've wired up as nearly all 'failures' alluded too were caused by either the early probe types (single wire conductor) &/or the cheap connectors or poor quality crimping tool. There has been conversations on crimping recently on VAF. I have commented several times on the causes of thermocouple 'issues' in the past.

Glenn wrote - "The fault was in each case an internal break of the very fine wire emerging from the probe. I switched to an aftermarket brand, and never looked back!"

Basically - the early probes, & Dynon egt/cht harnesses, had a single (1 strand of wire) wire conductor which really should be doubled over 2 or 3 times then crimped into a faston connector with a quality double jawed crimper.
EGT/CHT wiring & probes - they both are now supplied as being multi stranded wires.
Connectors - after some analysis I stopped using the supplied ones & changed over to the TE/AMP brand types. There are other types like the OLC's etc, however I've stayed with the push on types on my aircraft without any issues.
Ps - I usually spray the connections with contact cleaner before crimping as we're measuring millivolts here & I figure oxidisation of the joints may be a factor too. HTH.

 

[lrg775]

A service bulletin about the EGT probe design change sure would have been nice--my failure was of the single strand conductor mid-span.

I also thought it might just float to a random value, but it consistently tracks what the other EGTs are doing. I remember some fishiness like what Stevec saw when I swapped probes while troubleshooting--it acted in a different weird manner depending on what channel it was plugged into.

As for alarms, I agree I probably don't need them for high EGT. But...that's just a patch for this one particular failure. I'd like to leave audible alarms in place for many other sensors, and absolutely need a way to silence them if they get out of hand.

Any comment from Dynon here? Specifically about alarm inhibit, and maybe also about the behavior of the EGT amplifier when probes are disconnected.

Thank you all, by the way--this has been helpful.

 

[Dynon]

There isn't currently away to inhibit alarms in a permanent way other than the way you've suggested, by having it on a muted input.

As for the behavior - it may have to do how the internal electricals work on the EGT probes when the connection is "open". I'm not certain. But, know that if you short the two sides of the probe wires, that should stabilize the reading.

 

[kellym]

Joe, you wrote -
"And Irg775, the Dynon EGT probes have been notorious for their short lives. In one of my airplanes, I've replaced every single one of them one or two times in 650 hours. YMMV."

I understand your pain however the Dynon probes do not have short lives in my experience as I've only replaced 2 of them in the 50 RV's I've wired up as nearly all 'failures' alluded too were caused by either the early probe types (single wire conductor) &/or the cheap connectors or poor quality crimping tool. There has been conversations on crimping recently on VAF. I have commented several times on the causes of thermocouple 'issues' in the past.

Glenn wrote - "The fault was in each case an internal break of the very fine wire emerging from the probe. I switched to an aftermarket brand, and never looked back!"

Basically - the early probes, & Dynon egt/cht harnesses, had a single (1 strand of wire) wire conductor which really should be doubled over 2 or 3 times then crimped into a faston connector with a quality double jawed crimper.
EGT/CHT wiring & probes - they both are now supplied as being multi stranded wires.
Connectors - after some analysis I stopped using the supplied ones & changed over to the TE/AMP brand types. There are other types like the OLC's etc, however I've stayed with the push on types on my aircraft without any issues.
Ps - I usually spray the connections with contact cleaner before crimping as we're measuring millivolts here & I figure oxidisation of the joints may be a factor too. HTH.

Over the past 20 years I installed a UBG-16 analyzer in the Mooney I owned previous to my RV, and had frequent problems with probes, doing a lot of recrimping spade connectors. I switched to the OLC connectors and problems went away. First couple years with RV with Dynon probes and connectors had problems even though I was doubling over all wires before crimping, had frequent problems. Switched all to OLC-2 connectors, and problems disappeared...no probe failure since. The $1 per OLC connector from EI is money well spent. Very positive connections with low resistance. When I made the change on fuel flow that had been intermittent, not only did the readings become rock solid, but the K factor had to be reduced from somewhere above 70K to somewhere around 67K and has been very accurate since.

 

[Dynon]

There isn't currently away to inhibit alarms in a permanent way other than the way you've suggested, by having it on a muted input.

One other way to get around this is to make the alarm latching. That'll also ensure that you'll see any momentary alarm (because it will remain in the alert area)