Hi all
I have a rv7a with a mgl glass panel
Some time ago I started to have some noise on the rpm, start good on ground but sometime in flight it sometime jump from 2000 to 3000 rpm irradictly.
i changed the rpm input to use the plasma spark plug output the issue remain.
I have tried to play with the rdac filter but didn't work.
I suspect electric noise.
You guys have an idea on what to check more?
Thanks
RPM issue
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Re: RPM issue
Can you get your hands on an oscilloscope ? That tends to show you immediately what it going on. It can be tricky to figure out problems like this if you do not have such a device - you end up guessing.
In the past one of our customers came up with a brilliant idea that seemed to work very well on these engines - he used two of the A/C leads going to the rectifier/regulator module and connected these to a simple, small 1:1 600 ohm audio transformer on one side and the other coil one end to ground and the other to the RPM input. This appeared to provide a stable signal removing any high frequency noise (can't make it though the transformer and there was no DC offset which tends to happen based on the state of charge and electrical loads).
In the past one of our customers came up with a brilliant idea that seemed to work very well on these engines - he used two of the A/C leads going to the rectifier/regulator module and connected these to a simple, small 1:1 600 ohm audio transformer on one side and the other coil one end to ground and the other to the RPM input. This appeared to provide a stable signal removing any high frequency noise (can't make it though the transformer and there was no DC offset which tends to happen based on the state of charge and electrical loads).
Re: RPM issue
Hi
I did some test today
I checked with a scope the signal
At 1000 rpm I have a pretty clean signal (which ill send later)
With 500usec pulse at 30hz. At 10v peak
Went flying and didnsome test again at more than 2000rpm the tach seem to become eratic(will provide video).
I rebooted the efis and rdac, the issue remain.
Ap, radio on or off change nothing.
Currently the signal is comming from a plasma electronic ignition.
The wire is a shielded wire with one side of the shield connected to 0v in the plasma db9.
I will try to connect the shield to the rdac gnd too.
One funny thing happend with I tried to set rpm2 filter and ballast dip swith to on.
As soon the key had the plasma hot (not turning) the efis showed me 0 or 60000 rpm.
Set the rpm2 switches to off and it return to the same previous behavior.
I did some test today
I checked with a scope the signal
At 1000 rpm I have a pretty clean signal (which ill send later)
With 500usec pulse at 30hz. At 10v peak
Went flying and didnsome test again at more than 2000rpm the tach seem to become eratic(will provide video).
I rebooted the efis and rdac, the issue remain.
Ap, radio on or off change nothing.
Currently the signal is comming from a plasma electronic ignition.
The wire is a shielded wire with one side of the shield connected to 0v in the plasma db9.
I will try to connect the shield to the rdac gnd too.
One funny thing happend with I tried to set rpm2 filter and ballast dip swith to on.
As soon the key had the plasma hot (not turning) the efis showed me 0 or 60000 rpm.
Set the rpm2 switches to off and it return to the same previous behavior.
Re: RPM issue
https://youtu.be/PoefI6ysTtE
Btw I wasnt piloting in the video and it was a windy day
Here for the video
Connecting the shield to both end (on in the db9 the other at rdac gnd terminal) haven't fix my problem.
I will send the picture of the scope trace soon.
But I don't have the impression that noise is my problem here.
I have triples checked for loose connection too. (As its only over 2000rpm)
The rdac was inspected by mgl two year ago (mostly for pressure reading error)
What could be the cause and what to check?
Btw I wasnt piloting in the video and it was a windy day
Here for the video
Connecting the shield to both end (on in the db9 the other at rdac gnd terminal) haven't fix my problem.
I will send the picture of the scope trace soon.
But I don't have the impression that noise is my problem here.
I have triples checked for loose connection too. (As its only over 2000rpm)
The rdac was inspected by mgl two year ago (mostly for pressure reading error)
What could be the cause and what to check?
Re: RPM issue
The second image seem to miss some pulse but I think it was due to my scope being too slow for that time range
- Attachments
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- 1000rpm2.jpg (111.27 KiB) Viewed 3092 times
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- 1000RPM.jpg (116.72 KiB) Viewed 3092 times
Re: RPM issue
I am afraid I don't have a fix for this...but I have exactly the same problem.
I have an Explorer Lite with RDAc XG, engine is a Jabiru. All worked perfectly for the first 2 years and now I get erratic RPM above 2000rpm for the first 5 mins of a flight. It then settles down and works fine.
I also have an ECB Box which I can switch the main power supply on and off. Switching it off each individual CB doesn't help, but turning off the entire ECB seems to cure the problem. I can answer why just yet and havent had much time for more diagnosis.
I have an Explorer Lite with RDAc XG, engine is a Jabiru. All worked perfectly for the first 2 years and now I get erratic RPM above 2000rpm for the first 5 mins of a flight. It then settles down and works fine.
I also have an ECB Box which I can switch the main power supply on and off. Switching it off each individual CB doesn't help, but turning off the entire ECB seems to cure the problem. I can answer why just yet and havent had much time for more diagnosis.