John,
If now:
1. Only one sender wire connected (all others disconnected from unit)
2. Earth connected directly to battery
3. Engine off along with all other electronics
4. A known, good, +12V connection to battery
and you are still seeing fluctuating readings then time to send it back for repair or replace with new item.
I suspect you troubleshooting/diagnosis phase is now complete!
Tony Nowak
Avionics expert needed.
Moderators: John Dean, Moderator
Hi Tony
The oil pressure reading with the engine off is zero as expected and does not fluctuate. The water temp is also fluctuating with the engine running but is steady with the engine off.
This suggests to me that it is likely to be an installation issue rather than a fault with the unit. Is this correct thinking?
The oil pressure reading with the engine off is zero as expected and does not fluctuate. The water temp is also fluctuating with the engine running but is steady with the engine off.
This suggests to me that it is likely to be an installation issue rather than a fault with the unit. Is this correct thinking?
John Massey
030809
030809
John,
Is the unit that is causing you grief a sealed unit or can you open it up? If the latter, may be worth having a good look to see if there are any lose wires, components or connectors.
Beyond that I suspect your troubleshooting options are a bit limited.
Can you easily remove the unit from your aircraft and take it home? If so, you could try connecting it up to a battery and see what happens. Try the tap test.
Where abouts do you live?
Tony Nowak
Is the unit that is causing you grief a sealed unit or can you open it up? If the latter, may be worth having a good look to see if there are any lose wires, components or connectors.
Beyond that I suspect your troubleshooting options are a bit limited.
Can you easily remove the unit from your aircraft and take it home? If so, you could try connecting it up to a battery and see what happens. Try the tap test.
Where abouts do you live?
Tony Nowak
hi
I have had a chat with Ranier, the chap at MGL who designed the unit and he says that the problem cannot be in the display unit as it just displays what the RDAC tells it. He is at a loss to why I may be getting these fluctuations but is saying that it is usually
1. A corroded or bad connection
2. Ground loops
3. Really large voltage fluctuations supplying the RDAC
I have a friend with an oscilloscope and the next step is to establish exactly what is being input into the RDAC from the sensors and also to check for any voltage spikes.
The fluctuations in the water temp only happen with the engine running so taking the unit out is not going to help me. It is either an installation issue or a joint somewhere that does not like vibration. I am based in Surrey, near Cranleigh.
It keeps me occupied I suppose!
John
I have had a chat with Ranier, the chap at MGL who designed the unit and he says that the problem cannot be in the display unit as it just displays what the RDAC tells it. He is at a loss to why I may be getting these fluctuations but is saying that it is usually
1. A corroded or bad connection
2. Ground loops
3. Really large voltage fluctuations supplying the RDAC
I have a friend with an oscilloscope and the next step is to establish exactly what is being input into the RDAC from the sensors and also to check for any voltage spikes.
The fluctuations in the water temp only happen with the engine running so taking the unit out is not going to help me. It is either an installation issue or a joint somewhere that does not like vibration. I am based in Surrey, near Cranleigh.
It keeps me occupied I suppose!
John
John Massey
030809
030809
-
Simon Clifton
- Posts: 91
- Joined: Sun Feb 24, 2008 5:59 pm
- Location: Worcestershire
John
Ranier is a good guy, he is probably right.
If you do have a ground problem - the sort defined as a change in resistance in the return path through the engine/airframe/battery lead, then I don't think you're going to see that on a 'scope.
You will see spikes though, if there are any.
Simon C
~~~~~~
Ranier is a good guy, he is probably right.
If you do have a ground problem - the sort defined as a change in resistance in the return path through the engine/airframe/battery lead, then I don't think you're going to see that on a 'scope.
You will see spikes though, if there are any.
Simon C
~~~~~~
-
bertdeleporte
- Posts: 68
- Joined: Wed Jul 30, 2008 12:33 pm
- Location: France
Hi John,
did you try to filter your power supply? As Simon, I am not sure you will see some relevant information with a scope. Maybe, once again, the fact to put the scope will make the oscillation vanish. Moreover, the scope will show you fluctuating input at a very fast rate if not triggered and repetitive. The best would be to record the inputs (power supply or sensor and gauge terminals) and review the graphs to find a relationship between them. Most of the numerical scopes offer that function.
However, when using the scope, if you have dual channels, make EXTRA CARE of not creating a shortcut between the "ground" terminals of both channels on the PCB or the unit. On most of the scopes, the two channels share the outter lead connection of both BNC terminals. It is thus very easy to make a shortcut, as it is very tempting to plug the channels on circuits which are not at the same potential. The best is to connect earth+line of one channel, and only the line of the other channel. You get both signals displayed according to only one reference, but you are sure to make no hurt to the unit.
Bertrand
did you try to filter your power supply? As Simon, I am not sure you will see some relevant information with a scope. Maybe, once again, the fact to put the scope will make the oscillation vanish. Moreover, the scope will show you fluctuating input at a very fast rate if not triggered and repetitive. The best would be to record the inputs (power supply or sensor and gauge terminals) and review the graphs to find a relationship between them. Most of the numerical scopes offer that function.
However, when using the scope, if you have dual channels, make EXTRA CARE of not creating a shortcut between the "ground" terminals of both channels on the PCB or the unit. On most of the scopes, the two channels share the outter lead connection of both BNC terminals. It is thus very easy to make a shortcut, as it is very tempting to plug the channels on circuits which are not at the same potential. The best is to connect earth+line of one channel, and only the line of the other channel. You get both signals displayed according to only one reference, but you are sure to make no hurt to the unit.
Bertrand
I have put a noise filter on the power supply and also tried running the engine without the alternator connected. No difference.
Rainer has suggested using an oscilloscope. I have a friend with one but I don't understand anything complicated( or even simple for that matter !)
If any of you know how to test for earth loops that I might understand then I would love to hear. I cannot test the unit out of the plane as the problem only occurs with the engine running.
Also if any of you might have the expertise and/or gear to find the problem then I would be happy to fly anywhere in SE England to you. I have spent so much time looking at the issue that I feel I cannot see the wood for the trees. Having no understanding of electronics is a great handicap too!
cheers
John
Rainer has suggested using an oscilloscope. I have a friend with one but I don't understand anything complicated( or even simple for that matter !)
If any of you know how to test for earth loops that I might understand then I would love to hear. I cannot test the unit out of the plane as the problem only occurs with the engine running.
Also if any of you might have the expertise and/or gear to find the problem then I would be happy to fly anywhere in SE England to you. I have spent so much time looking at the issue that I feel I cannot see the wood for the trees. Having no understanding of electronics is a great handicap too!
cheers
John
John Massey
030809
030809
1. When you run your engine, can you detect any ignition interference on your radio? Just wondering if the RDAC is picking up ignition intereference.
2. I think you said you have already swapped out the RDAC and the same problems exist? correct?
I think you are getting very close to eliminating what it isn't! If you ONLY have one sensor connected and that sensor ONLY fluctuates when the engine is running, there can't be many areas left to investigate.
Did you manage to check the unit(s) using a completely separate, independant, battery supply? That will eliminate any potential issues with your installed electrical system.
Earth loops can't easily be tested for without resorting to expesive test equipment, however an inspection of how the RDAC is wired up will tell you if earth loops are likely to be the cause.
Does the RDAC have a metal case / enclosure?
Is it attached directly to your metal structure?
How is the RDAC earth wire connected to your airframe/electrical system?
I don't live all that far from you. If you really get stuck I am happy to come over and see if I can spot anything.
Tony Nowak
2. I think you said you have already swapped out the RDAC and the same problems exist? correct?
I think you are getting very close to eliminating what it isn't! If you ONLY have one sensor connected and that sensor ONLY fluctuates when the engine is running, there can't be many areas left to investigate.
Did you manage to check the unit(s) using a completely separate, independant, battery supply? That will eliminate any potential issues with your installed electrical system.
Earth loops can't easily be tested for without resorting to expesive test equipment, however an inspection of how the RDAC is wired up will tell you if earth loops are likely to be the cause.
Does the RDAC have a metal case / enclosure?
Is it attached directly to your metal structure?
How is the RDAC earth wire connected to your airframe/electrical system?
I don't live all that far from you. If you really get stuck I am happy to come over and see if I can spot anything.
Tony Nowak
-
Will Greenwood
- Posts: 147
- Joined: Mon Jan 07, 2008 6:08 pm
- Location: EAST SUSSEX UK
- Contact:
Hi
I have now spoken Nicol, the R & D man at MGL and it does seem as though I have an earth loop issue. I have tried hooking the oil pressure sender up to a totally separate MGL TP1 electronic gauge and get the same fluctuations. Given that I have also tried running the RDAC off a separate battery and also have run the engine with the alternator disconnected it is unlikely to be a power issue.
The RDAC is in a plastic box and the earth wire runs to the engine block, as directed in the manual. It is attached to the firewall on metal standoffs supplied with the unit.
I will be away next week but am tempted to follow Will's advice and have Adrian at South Coast Avionics take a look. Although he is not familiar with the MGL kit, he will be au-fait with the dreaded ground loops which it seems can wreak havoc.
Thanks for everyones help. I will report back as soon as I find the answer so that hopefully others can learn from my woes.
cheers
john
I have now spoken Nicol, the R & D man at MGL and it does seem as though I have an earth loop issue. I have tried hooking the oil pressure sender up to a totally separate MGL TP1 electronic gauge and get the same fluctuations. Given that I have also tried running the RDAC off a separate battery and also have run the engine with the alternator disconnected it is unlikely to be a power issue.
The RDAC is in a plastic box and the earth wire runs to the engine block, as directed in the manual. It is attached to the firewall on metal standoffs supplied with the unit.
I will be away next week but am tempted to follow Will's advice and have Adrian at South Coast Avionics take a look. Although he is not familiar with the MGL kit, he will be au-fait with the dreaded ground loops which it seems can wreak havoc.
Thanks for everyones help. I will report back as soon as I find the answer so that hopefully others can learn from my woes.
cheers
john
John Massey
030809
030809
In all the above I can't see any mention if the wire between the RDAC and the display has been changed at all.
Some of what's been reported would seem to indicate against that as a problem, but the 5 minute 'RDAC failure' and all the comments about earth loops coupled with the intermittent nature of the problems (works OK for an hour then carp again) makes me think that there could be a loose earth either in the main lead between the units, or a plug is not making proper contact at one end or the other.
I'll come clean and say I don't have any 'glass cockpit' experience other than reading up on the Odyssey and Voyager (and want one). Am I correct in thinking Stratomaster kit uses 'phono' plugs for the data connection between the 2 units?
I've played with hi-fi long enough to know the vagaries of these little connectors, and that high-end, professional, and even home-made audio equipment tends to use XLRs partly as they are electrically a better solution, and they are a hell of a lot more reliable!
Some of what's been reported would seem to indicate against that as a problem, but the 5 minute 'RDAC failure' and all the comments about earth loops coupled with the intermittent nature of the problems (works OK for an hour then carp again) makes me think that there could be a loose earth either in the main lead between the units, or a plug is not making proper contact at one end or the other.
I'll come clean and say I don't have any 'glass cockpit' experience other than reading up on the Odyssey and Voyager (and want one). Am I correct in thinking Stratomaster kit uses 'phono' plugs for the data connection between the 2 units?
I've played with hi-fi long enough to know the vagaries of these little connectors, and that high-end, professional, and even home-made audio equipment tends to use XLRs partly as they are electrically a better solution, and they are a hell of a lot more reliable!
Rob Swain
If the good Lord had intended man to fly, He would have given him more money.
If the good Lord had intended man to fly, He would have given him more money.
-
Simon Clifton
- Posts: 91
- Joined: Sun Feb 24, 2008 5:59 pm
- Location: Worcestershire
Rob
I have an MGL electronic compass. It uses a remote magnetic sensor, built into a neat box not a lot bigger than a 9-way D-type shell.
The connection between the remote sensor and the instrument is a 'RCA' phono cable, supplied in the kit. I believe it is a digital bus multi-drop interface, so although it wouldn't be my choice of connector (there is no built-in strain relief, and the outer connection can be less-than tight), it does seem to work okay. The installation instructions mention squeezing the outer connector with pliers to create a tight fit if needed.
Pulling pre-moulded RCA cables through thin conduit is another matter!
I have to say I am impressed with the instrument.
Cheers
Simon C
~~~~~~
I have an MGL electronic compass. It uses a remote magnetic sensor, built into a neat box not a lot bigger than a 9-way D-type shell.
The connection between the remote sensor and the instrument is a 'RCA' phono cable, supplied in the kit. I believe it is a digital bus multi-drop interface, so although it wouldn't be my choice of connector (there is no built-in strain relief, and the outer connection can be less-than tight), it does seem to work okay. The installation instructions mention squeezing the outer connector with pliers to create a tight fit if needed.
Pulling pre-moulded RCA cables through thin conduit is another matter!
I have to say I am impressed with the instrument.
Cheers
Simon C
~~~~~~
John, did you ever fix it?
I was just looking at the RDAC schematic diagram, and I notice that the oil temp & pressure are single wire sensors, whereas CHT and EGY are 2 wire sensors.
All the sensors work in tone of 2 ways way, the 2 wire sensors generate a small voltage, the single wire sensors alter their resistor which means a varying small voltage appears across the sensor inputs.
So if you have CHT and or EGT and the readings are steady whilst the oil T7P fluctuate then it must be something affecting either the 12v supply to the RDAC or the earth return path.
I would guess that the RDAC has some supply smoothing capacitor, so momentary interruptions to the supply will cause the voltage across the RDAC to decay perhaps taking a couple of secs, during that time the current flowing through any resistive type sensors will decay, but as long as there is still 8v supply voltage, the RDAC will continue to send data, but with only 8v, the RDAC will indicate only 8/12 of the proper reading, so for example the oil pressure could change from 60psi to 40psi.
So it could be a dry joint on the RDAC or on the ground lead or 12v supply coming from the Ultra or between the battery and the Ultra - possibly a loose fuse fitting.
Or it could be something causing large swings in the voltage supplied to the ultra - remember that will continue to work down to 8v, it could even be loose battery connectors.
One simple test is to connect an AVO ( analog meter) across the RDAC supply and watch the needle - hold the thing otherwise the vibrations from the engine will send the needle evry which way. Digital meters are useless in this context as they have very slow refresh rates so they miss intermittent spikes. If you see any movement of the needle, try using a separate 12v battery to supply just the RDAC and see what happens then.
If you do see fluctuations and rule out bad connections, it could be your alternator ( worn brushes ) or strobe lights, transponder
Good luck
I was just looking at the RDAC schematic diagram, and I notice that the oil temp & pressure are single wire sensors, whereas CHT and EGY are 2 wire sensors.
All the sensors work in tone of 2 ways way, the 2 wire sensors generate a small voltage, the single wire sensors alter their resistor which means a varying small voltage appears across the sensor inputs.
So if you have CHT and or EGT and the readings are steady whilst the oil T7P fluctuate then it must be something affecting either the 12v supply to the RDAC or the earth return path.
I would guess that the RDAC has some supply smoothing capacitor, so momentary interruptions to the supply will cause the voltage across the RDAC to decay perhaps taking a couple of secs, during that time the current flowing through any resistive type sensors will decay, but as long as there is still 8v supply voltage, the RDAC will continue to send data, but with only 8v, the RDAC will indicate only 8/12 of the proper reading, so for example the oil pressure could change from 60psi to 40psi.
So it could be a dry joint on the RDAC or on the ground lead or 12v supply coming from the Ultra or between the battery and the Ultra - possibly a loose fuse fitting.
Or it could be something causing large swings in the voltage supplied to the ultra - remember that will continue to work down to 8v, it could even be loose battery connectors.
One simple test is to connect an AVO ( analog meter) across the RDAC supply and watch the needle - hold the thing otherwise the vibrations from the engine will send the needle evry which way. Digital meters are useless in this context as they have very slow refresh rates so they miss intermittent spikes. If you see any movement of the needle, try using a separate 12v battery to supply just the RDAC and see what happens then.
If you do see fluctuations and rule out bad connections, it could be your alternator ( worn brushes ) or strobe lights, transponder
Good luck
Peter Diffey
029340
029340