Update on CHT & EGT jumping when I press the PTT

[jakej]

Thanks Dennis, however I am aware of that, but I figured these 'issues' were with earlier units

I'll pm you.

Jake J

 

[DennisW]

Jake, the issue is not with the display, but with RF getting into the EMS.

 

[preid]

I have no idea how new my display is, but I dont think I have any filters, regardless if the capacitors on the EMS did not resolve the issue than how do we know that RF is getting into the EMS? the capacitors should have cleared that up. at least a little bit anyway.
So we know filters on displays- no resolution, capacitors on the EMS, some say it works others do not. I have literally moved everything around, turned everything off except the SL-40 and Dynon and even with antennas feet away I still get the spikes.
I am interested in seeing this resolved, because this has turned into something quite fascinating for me. I don't think it's RF interference, I have no idea what it is but my moving everything far away capacitors not working for some and still getting the same results leads me to think it is not RF.
Fortunately, this is not a safety issues, except the passengers that yell my engine is going to blow and I have to calm them down as saying I'm just full of hot air when I talk and the spikes are normal ;D..

 

[jakej]

Have you tried turning off the alternator (when on the ground) then using the PTT ?

Sounds weird I know but these 2 others (using different sytems, 1 x Dynon legacy & 1 x Rocky Mountains) are an example---

Aircraft 1 - CHTs were working ok before engine pulled but when engine replaced #1 & #3 CHTs were all over the place, (CHTs were just removed from Cylinders, wiring not disconnected) sheilded wire to Alt field fixed it.

Aircraft 2 - Alt Field circuit breaker would pop sometimes when using PTT, sheilded field wire fixed that too. Another aircraft wired with the same systems etc, at the same time, had no issues. Go figure !

I'm not saying this will fix the problem/s however just illustrating that sometimes the solution can be unexpected.

HTH

Jake J

 

[DennisW]

My system has the alternator tied to the master switch (one switch, not two). I have tested the system without the engine running and the temps still jump.

 

[preid]

Agree!
I have done most of the troubleshooting on the ground with nothing but 1 screen and the SL40 running and the spikes are there. I don't recall if I did it with the SL40 off, although I am pretty certain I did.

 

[jakej]

Bear with me guys, I'm only trying to help here to find a solution.

Where do you have the PTT grounded ?

Jake J

 

[DennisW]

I need to look, but I think both PTTs are grounded to my ground buss mounted under the pilot's seat. This is the master ground buss, I have another mounted behind my 10 inch screen on the instrument panel mount. Both are strapped together and tied to the engine block.

 

[jakej]

Dennis

In composite aircraft I 'bond' all the 'boxes' and instrument panels with braided straps, reduces chances of the types of issues you are seeing.

It may be worthwhile using a MuMetal cover on the EMS & ADAHRS cosidering where you have these mounted in relation to the Com antennas. However I tried the bonding straps first.

FYI - MuMetal is also used in power transformers (mounted on steet poles in places here) & is much more cost effective then buying from aviation suppliers

HTH

Jake J

 

[dynonsupport]

Please don't cover your ADAHRS with Mu-metal. The H is for Heading and the whole point of Mu-metal is to block magnetic fields (it's 16% iron).

 

[jakej]

I should have thought about that more & stated it would be ok around the EMS module only, however I've never had to use Mu Metal in any aircraft yet either.

Jake J

 

[DennisW]

I am an electrical engineer, I would not have covered the ADAHRS with mu-metal. I have used this before in other applications. The ground straps can't hurt and might help. I'll do that and let everyone know if anything changes.

 

[mikeperkins]

It might be worth checking the SWR (standing wave ratio) on the comm radio's installation. A high SWR can cause excessive emissions from the cable and also from the radio itself. Usually an SWR of 1.5 is good enough, but the closer to 1.0, the better (1.2 is about as good as it gets.) To measure SWR, one must have an SWR meter - all avionics techs will have one and know how to use it. SWR can be adjusted by changing the length of the coax (shortest is not always the best for getting a low SWR), plus other ways the tech will know about. It is also possible on fiberglass stripline antennas to trim their length for the lowest SWR. Also, double-shielding the coax with braided shield and grounding it on one end, say to the antenna ground plate, can help reduce the unwanted emissions from coax.  But it's always best to get the SWR below 1.5 first.

 

[DennisW]

I know how to use a SWR meter, but I don't have one. I will eventually get this done at the avionics shop. Thanks.

 

[DennisW]

Ok, the other day I checked the change in CHT/EGT change for Comm 1 and Comm 2. Comm 1 had a change of over 100 degrees when pushing the PTT. Comm 2 was around 10 degrees difference. The difference between the two? The RF cable for Comm 1 runs very close to the cable that runs from the ADAHRS to the EMS computer. The antenna is within 2 feet of the ADAHRS. The Comm 2 cable runs on the other side of the aircraft and the antenna is in the vertical stabilizer. This afternoon, I moved the RF cable for Comm 1 to the other side of the aircraft. Now the delta is around 12 to 15 degrees when I push the PTT on Comm 1. I still have some vertical speed movement when I push the PTT so I am going to move the L-Comm filter for the 9 pin connector from the EMS module to the ADAHRS. I'll let you know what I find after I do that. Another option is to buy the MGT ferrite bead filters and clip them on the end of the RF cables next to the antennas. I will likely order a couple of these later this week. Actually, I am having fun working out these little issues.

 

[DennisW]

Yesterday, I moved the L-Comm filter from the EMS to the ADAHRS. This fixed the vertical speed movement when I pushed the PTT. It did not make any difference in the EGT and CHT changes, so no worse, no better. Maybe a little filtering in the computers might be a good thing for those of us with plastic airplanes. I think when I am at Sun N Fun, I'll pick up those ferrite filters.

 

[preid]

" Maybe a little filtering in the computers might be a good thing for those of us with plastic airplanes."

I have an aluminum plane and it does the same thing! RG-400, plenty of space, avionics shop confirmed there was no noise coming from the SL-40 connections to the antenna.

There is something else causing the issue.

 

[HeritageAviation]

We have a 2009 Flight Design CTLS here. We have the EMS 120 but, my understanding is the the EGT and CHT circuitry in the 120 and skyview are pretty equivalent. The CHT and sometimes the EGT sky rocket when the PTT is pressed and more commonly when the electric flaps are moved. We just purchased a set of 3 filters from L-Com today and will be installing them and testing the result as soon as they get here. I will be sure to report back as to whether or not they helped our situation.

 

[dynonsupport]

Unfortunately, the filters are unlikely to help in this case.

The CHT's on a Rotax are not thermocouples, they are thermistors (variable resistors). The fact that they change is much more indicative of a bad ground than EMI, as they are highly resistant to EMI. The fact that your electric flaps effects them, as well as transmitting on the radio which draws a lot of current, points a lot to a ground issue.

The filters will only help if the interference you are getting is RF on the cables. It can't filer out DC issues like a ground problem.

It's possible that your engine is badly enough grounded that the voltage between it and the rest of the airplane gets high enough to also mess up the EGT's. I'd look into grounding, and get the CHT's fixed before you worry about the EGTs.

 

[ultraliviano]

I have the same problem than Richard Fazzio, I have Sky View in a Europa with a Rotax engine When I pressed the PTT for my com radio the EGT temps jumped up.
I did some trial tests run antenna coax far from wiring etc.
with no results, I tried with a handy powered with bateries  and the EGT still jump.. I really do not know what else to do..