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Electronics project; DIY EGT / CHT engine monitor

BruceMe

Well Known Member
I'm handy with programming and electronics and I kinda want to experiment with a poor man's engine monitor. When I've bought engine monitors in the past, I just forked over the $800 for engine probes, I kinda want to try doing it on the cheap this time and sourcing my own.

The Lycoming head takes 3/8" NPT threaded bayonet-style probes. How long can they be?

How does this look?


Cheaper EGT with strap...


Just the EGT probe...


And the strap/clamp


Note: I'm not positive that the clamp matches the thermocouple.

All 8 of these these thermocouples channels will go through this signal processor to generate digital signals I'll read with an MC and display on my android tablet / phone.

In total it will cost between $100 and $200 (depending on how the sensors actually work out).

I'm posting if anyone has any better ideas on how to source high temperature probes for $20 per.

Also... any ideas, I'd love to hear them!

Thanks!
 
Remember thermocouples just measure the temperature difference between, say, the exhaust, and a reference junction (usually at the electronics box). Since cockpit temperatures can vary a fair bit, the better boxes use a thermistor or equivalent to measure the reference temperature. Inexpensive boxes just assume it's 72 F.
 
And also remember cold junction compensation... if you run your thermocouple through a connector that doesn't use thermocouple-material pins, you induce a temperature bias equal to the temperature of the connector. For EGT this isn't super-critical since EGT's are used relative to their neighboring cylinder's EGT readings. CHT is more critical since we're interested in absolute, rather than relative readings. It's kind of important to know that 400 degrees really is 400, not 400 plus or minus some amount of bias.
 
BruceMe - I would really, really encourage you to push forward on a DIY engine monitor. I believe that for homebuilt aircraft, an engine monitor is a very significant component of the overall safety picture.

There are many engine monitors commercially available, but they are expensive and often marry you to an overall (EFIS) instrument system that one may not want or may be difficult to retrofit into one's existing panel.

It would be nice to have all the engine parameters (CHT,EGT, Oil T&P, Tach, Hobbs, etc), but I think the most useful, simplest device is the way to start a DIY. For such, I would vote for 4 CHT channels and tach with time stamped memory. Memory is important. Experimental planes often have cooling issues to troubleshoot and this needs to be addressed asap.

One other feature that would be great, especially for pusher engines, is to separate the display/microcontroller module from the DAC/thermocouple unit.
(MGL does this.) The DAC unit should be in the engine compartment to keep the thermocouple leads short and directly connected to the (temp. compensated) DAC without intermediate dissimilar metal connections. Consequently, simple copper wires can then be run from the DAC unit to the display unit.

BTW, don't worry about the thermocouples. They are cheap and can also be DIY out of J-type thermocouple wire and spark plug washers. The Aerolectric Connection book also discusses how to make bayonet types that screw into the cylinder thermocouple wells. Your challenge is the instrument, not the sensors.
 
EGT probe without exhaust pipe penetration?

Hi Bruce, Do you think it would be possible to determine the EGT by having a probe connected to the exhaust pipe - externally? Mainly to avoid the hole in the pipe and the clamp. I know the normal EGT probes have been used for years without problem, just curious if it would be possible. Surely there would be more lag than a regular probe.
 
i was planning on working up a prototype with an Arduino until my VM1000 bit the dust this spring. i had even developed some code to talk to my GRT Sport. i didnt want to go the whole summer debugging an engine monitor without something reliable so i just went out and bought an EIS400 from Grand Rapids. oh well.... at least it works really really well :eek:

Don
 
EGT/CHT display optimization

Hi All

I'm working on my DIY EMS and trying to optimize my display screen.

So here is a question - from practical standpoint would you prefer
1. to see all the individual temperatures on all cylinders (see image below), or
2. it would be OK just to see the highest one and other temperatures displayed as relative bar graphs???

The second approach would help greatly to save some real estate on the display

Here is an example of the first approach:
EMS-600x266.jpg
 
Being an old electronics tech myself, I admire the efforts.
One thing the "top of the line" engine monitors have done is spent a lot of time on how and where information is displayed. It is relatively easy to get the raw data out, but what makes or breaks it for me is in the presentation, especially alarms. I know one of the Beta testers for one of these companies and they spend a great deal of time "flying" their monitors from the couch.
Color is good! Being able to perform my scan and see "all in the green" simplifies my scan when I am in a busy environment. I would carefully consider, if your not going to the expense of a color display, how you present alarms.
Another item that I have found very useful is the data logging. Again, not just the data, but the presentation of that data which helps analyze trends or look at specific events for a given flight or portion thereof. You need memory, and lots of it, unless you dump frequently. Then you need a piece of software to crunch it and display it in a manner that makes it easy to digest.
Anyway, Those are a couple things that make a good engine monitor more than just displaying the data. It is also what drives the cost up - significantly!
Have fun with the project. This is truly what experimental aviation is supposed to be about.
 
Oleg, I like your display. Keeps things cheap and direct. Sure, you can explore other ways of displaying the cht/egt data. There is more than one useable way of displaying things.
Perhaps you can superimpose cht on the same egt bars to save space. The cht can be a white space somewhere in the middle of the egt bar, for example. Then you can display only the highest egt/cht values as you suggest, or display the values for each cylinder in a sequence or select to show only egt or cht values.
I do agree that color and especially data logging, are important. However, you've done a great job so far. Please keep at it.
 
Thanks JonJay,

It is interesting though about alarms and "all green". Thanks!

I can simply define a few checks and illuminate an LED light next to the display if these checks fail.
This way I can keep the simplicity of the monochrome LCD display and display the alarms keeping all the detail data on the screen.
I guess it is like a "Check Engine" light in a car.

I'll add this idea into my "todo" list. :)

Cheers,
 
Thanks JonJay,

It is interesting though about alarms and "all green". Thanks!

I can simply define a few checks and illuminate an LED light next to the display if these checks fail.
This way I can keep the simplicity of the monochrome LCD display and display the alarms keeping all the detail data on the screen.
I guess it is like a "Check Engine" light in a car.

I'll add this idea into my "todo" list. :)

Cheers,

You bet. I wasn't being critical at all. Just throwing out some ideas. I love what your doing.
 
Hi,

I didn't take it as a criticism. I actually think a set of alarm lights is a good idea.

I got carried away trying to replicate Dynon and Garmin and fit everything in one screen, so I completely forgot about good old annunciator. :)

It is also a cheap and easy way to expand the functionality of the system.

Now that makes me think about audio notification. Simple beep-beep stuff, nothing fancy.

Is it good idea to have an audio alarm or it just unnecessary increases stress level?
 
Audio alarms are tough little beasts to integrate. Not technically, of course, but from a human factors perspective. We got to a point in legacy airline cockpits that we had a ton of beepers and bongers and squealers and chimes. So much so that nobody could tell, in an emergency situation, which device was sounding the alarm. In fact, some pilots have told me that most of this type of audio alarming was really only of any use to the teams doing post-crash analysis of the cockpit voice recorders.

Along came more modern technology and we started to use human voices to tell us exactly what was wrong... "Oil Pressure, Oil Pressure". This approach works much better than beepers and bongers.

With respect to engine data presentation, many helicopter pilots who were experienced in lifting external sling loads would rotate the engine instruments so all the pointers pointed in the same direction (example, 3 o'clock) when the engines were running normally and within torque and temperature limits. When your living is made with your head outside the helicopter looking down at a sling load, it's really helpful to have a very quick glance at the instruments tell you that all is well in the power department.
 
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