After my own tribulations with getting a Blaze EMS-2 to give consistent readings and hearing many more stories both here and by talking to others, I'm beginning to wonder if they are simply very intolerant to interference and some sort of shielding of the unit would be a help as the case is entirely plastic.
I considered simply applying foil tape to the rear portion of the case but as that would still leave the front face unshielded so not sure if it's even worth trying.
Anyone have any thoughts on this subject?
Shielding
Forum rules
Please keep your posts friendly and on topic. No politics or discussions of a controversial nature not related to our favorite subject of flying and avionics. Offending posts may be removed or moderated.
Please keep your posts friendly and on topic. No politics or discussions of a controversial nature not related to our favorite subject of flying and avionics. Offending posts may be removed or moderated.
Re: Shielding
No they are not intolerant to interference.
If you are not getting consistent readings - consider what the EMS sees. What does it measure ? It measures a voltage between an input and it's own power supply ground. That voltage is either created by some sensor or it is a voltage drop over a resistive sensor connected to ground (usually the engine block). The voltage is as a result of the EMS injecting a small current through the resistor.
Thermocouples are differential sensors - often they are grounded at the thermocouple itself (to the engine block). This means one of the two wires goes negative while the other goes positive - and we are talking just micro-volts per degree.
The most common issue is incorrect grounding of the item that measures the voltage. Does not matter if it is the EMS or an RDAC. The same thing applies.
To make it work - it's very simple. The EMS (or RDAC) get's it's power supply ground from the engine block. One wire. You do NOT share that wire with any other electrical user. You do NOT connect that wire to the airframe, power supply ground distribution point (or bus bar), you do not connect it to the battery negative or anything else. One ground wire from the EMS or RDAC to the engine block. No more no less.
If your EMS or RDAC has other ground terminals (like the RDAC gives you a few more) do NOT connect these to another ground point. These terminals are intended to be connected to ISOLATED sensors. Typical example would be a resistive fuel level sender - often these have a nice big metal flange screwed to the side of a metal fuel tank which happens to be connected to ground. That flange is the negative connection of the variable resistor. Not good. Fine for a car but not for an aircraft - isolate that ground connection and run a ground wire back to the RDAC or EMS.
What happens if you do not do that ? If your RDAC or EMS is the ONLY electrical user in your system (not even a alternator/battery charger or any sort) then you do not have a problem. The moment there are other currents flowing in various ground connections your EMS or RDAC ground now no longer sees the voltage drop from your sensor but instead sees that voltage PLUS whatever voltages are dropped over your various other ground connections. Currents are flowing in all sorts of directions and your grounding system is nothing but a complex resistive network.
Do not for a moment underestimate the effect this can have on your readings - it can be really bad.
The only other thing that causes havoc is a (much) less than perfect DC supply - that is more common than you think. The only way you will find out is to connect a scope to your power supply. A voltmeter tells you absolutely nothing in this regard. Errant ignition system currents, regulator artifacts and electrical noise generated from faulty or badly designed equipment (some cheap USB chargers come to mind) can seriously affect the quality of your power. If bad enough - that will also affect your readings as these various signals that are on-top of your power can be very fast exceeding your devices ability to regulate and filter them out.
if it starts going wrong after several years of no issues - and you have checked your wiring for damage and corrosion - simply run your EMS/RDAC with your engine off. Heat one or two sensors and see what your readings do. If everything is stable now - start looking very closely at your regulator/rectifier - they do have the habit of failing. Even a battery that is getting tired can contribute as its internal resistance starts to increase - the battery forms a vital part of the regulator/rectifier circuit which tends to be just a fast on/off switch and relies on the battery to smooth things out.
If you are not getting consistent readings - consider what the EMS sees. What does it measure ? It measures a voltage between an input and it's own power supply ground. That voltage is either created by some sensor or it is a voltage drop over a resistive sensor connected to ground (usually the engine block). The voltage is as a result of the EMS injecting a small current through the resistor.
Thermocouples are differential sensors - often they are grounded at the thermocouple itself (to the engine block). This means one of the two wires goes negative while the other goes positive - and we are talking just micro-volts per degree.
The most common issue is incorrect grounding of the item that measures the voltage. Does not matter if it is the EMS or an RDAC. The same thing applies.
To make it work - it's very simple. The EMS (or RDAC) get's it's power supply ground from the engine block. One wire. You do NOT share that wire with any other electrical user. You do NOT connect that wire to the airframe, power supply ground distribution point (or bus bar), you do not connect it to the battery negative or anything else. One ground wire from the EMS or RDAC to the engine block. No more no less.
If your EMS or RDAC has other ground terminals (like the RDAC gives you a few more) do NOT connect these to another ground point. These terminals are intended to be connected to ISOLATED sensors. Typical example would be a resistive fuel level sender - often these have a nice big metal flange screwed to the side of a metal fuel tank which happens to be connected to ground. That flange is the negative connection of the variable resistor. Not good. Fine for a car but not for an aircraft - isolate that ground connection and run a ground wire back to the RDAC or EMS.
What happens if you do not do that ? If your RDAC or EMS is the ONLY electrical user in your system (not even a alternator/battery charger or any sort) then you do not have a problem. The moment there are other currents flowing in various ground connections your EMS or RDAC ground now no longer sees the voltage drop from your sensor but instead sees that voltage PLUS whatever voltages are dropped over your various other ground connections. Currents are flowing in all sorts of directions and your grounding system is nothing but a complex resistive network.
Do not for a moment underestimate the effect this can have on your readings - it can be really bad.
The only other thing that causes havoc is a (much) less than perfect DC supply - that is more common than you think. The only way you will find out is to connect a scope to your power supply. A voltmeter tells you absolutely nothing in this regard. Errant ignition system currents, regulator artifacts and electrical noise generated from faulty or badly designed equipment (some cheap USB chargers come to mind) can seriously affect the quality of your power. If bad enough - that will also affect your readings as these various signals that are on-top of your power can be very fast exceeding your devices ability to regulate and filter them out.
if it starts going wrong after several years of no issues - and you have checked your wiring for damage and corrosion - simply run your EMS/RDAC with your engine off. Heat one or two sensors and see what your readings do. If everything is stable now - start looking very closely at your regulator/rectifier - they do have the habit of failing. Even a battery that is getting tired can contribute as its internal resistance starts to increase - the battery forms a vital part of the regulator/rectifier circuit which tends to be just a fast on/off switch and relies on the battery to smooth things out.
Re: Shielding
Hi All,
From a fellow aircraft owner and further to the topic of EMF and shielding and EFIS issues.
I purchased a second hand aircraft with just under 1000 hours on it, it had been twice around Australia with it's two MGL Voyager EFIS and was told once set up properly when new, worked without issue.
Then a new engine was installed just before I purchased the aircraft. Many of us would think an engine change would have little affect on the operation of the EFIS. In my case the engine charge also included a different charging system.
What I found during the inspection and purchase of this aircraft, all the EFIS engine monitoring gauge seemed to be in-actuate or very flaky, but did read within their ranges.
On my third cross country flight, a few minutes after take off, I suddenly had wild fluctuating oil pressure and temperature alerts on both my EFISs for what seemed a life time. I turned back immediately to land and by the time we got to the circuit pattern, the wild fluctuating oil pressure and temperature had slowly started to read with range.
Back on the ground and after checking oil quantity and quality and checking and flexing some wiring terminals, I could make the oil temp fluctuate without the engine running. So with some trepidation we headed home without any further issues.
I guess I am lucky as I have some understanding of electronics and how the EFIS electrical sensor system works, but everyone should lean the basics if you have any type of Glass avionics, regardless of brand, as they all work basically the same way.
So what caused my sudden EFIS melt down. Well after much testing of all the CHT, EGT, Oil and Fuel Gauges sensor on the bench and all proved to be within tolerance. I then checked all the positive and negative bus terminations and cleaned them all.
I would also say, if your electrical wiring to your sensors in the engine bay look old, corroded, dirty or oily, this could be causing you EFIS issues. I would think about cleaning all your engine bay electrical bus connections every 5 years is a good idea. Start by disconnecting all your batteries from the aircraft electrical system, sometimes like my aircraft you may have a EFIS back-up power supply battery installed as well. This is not the EFIS button battery used for data back-up.
Then undo and clean up all the cable terminals you can find for corrosion or oxidation. If any of the cable terminators look old or even slightly corroded or oily or have broken wire strands, then cut the wire cable terminators off and crimp new ones on, but first check you have enough cable length to do this.
In my case, I found that the earth wires from my fuel gauge sensors were terminated back to the instrument panel negative bus and not the RDAC negative bus as they should have been. This was causing an earthing differentials for the RADC and so causing all my EFIS engine monitoring sensor to be unstable.
Cheers
JimJab
From a fellow aircraft owner and further to the topic of EMF and shielding and EFIS issues.
I purchased a second hand aircraft with just under 1000 hours on it, it had been twice around Australia with it's two MGL Voyager EFIS and was told once set up properly when new, worked without issue.
Then a new engine was installed just before I purchased the aircraft. Many of us would think an engine change would have little affect on the operation of the EFIS. In my case the engine charge also included a different charging system.
What I found during the inspection and purchase of this aircraft, all the EFIS engine monitoring gauge seemed to be in-actuate or very flaky, but did read within their ranges.
On my third cross country flight, a few minutes after take off, I suddenly had wild fluctuating oil pressure and temperature alerts on both my EFISs for what seemed a life time. I turned back immediately to land and by the time we got to the circuit pattern, the wild fluctuating oil pressure and temperature had slowly started to read with range.
Back on the ground and after checking oil quantity and quality and checking and flexing some wiring terminals, I could make the oil temp fluctuate without the engine running. So with some trepidation we headed home without any further issues.
I guess I am lucky as I have some understanding of electronics and how the EFIS electrical sensor system works, but everyone should lean the basics if you have any type of Glass avionics, regardless of brand, as they all work basically the same way.
So what caused my sudden EFIS melt down. Well after much testing of all the CHT, EGT, Oil and Fuel Gauges sensor on the bench and all proved to be within tolerance. I then checked all the positive and negative bus terminations and cleaned them all.
I would also say, if your electrical wiring to your sensors in the engine bay look old, corroded, dirty or oily, this could be causing you EFIS issues. I would think about cleaning all your engine bay electrical bus connections every 5 years is a good idea. Start by disconnecting all your batteries from the aircraft electrical system, sometimes like my aircraft you may have a EFIS back-up power supply battery installed as well. This is not the EFIS button battery used for data back-up.
Then undo and clean up all the cable terminals you can find for corrosion or oxidation. If any of the cable terminators look old or even slightly corroded or oily or have broken wire strands, then cut the wire cable terminators off and crimp new ones on, but first check you have enough cable length to do this.
In my case, I found that the earth wires from my fuel gauge sensors were terminated back to the instrument panel negative bus and not the RDAC negative bus as they should have been. This was causing an earthing differentials for the RADC and so causing all my EFIS engine monitoring sensor to be unstable.
Cheers
JimJab
Older MGL units