EGT Logging revisit
 

I found the previous thread talking shortly about adding EGT logging and probes to Megasquirt. As I understand MSnSE does nothing with this data except log it.

Since that thread a few months ago has anyone further done so? Is it even worth it?

I've got a greddy EGT gauge I'm going to use just because I have it so I'll at least be able to monitor my temps with that.

http://megasquirt.sourceforge.net/ex...gt-circuit.jpg

That plus extra wiring and hassle almost seems like more trouble than its worth?

I struggle to see the value in logging EGT, especially considering the extra work involved. I find my EGT gauge data interesting, but of little actual value.

Talk to Reverant. He logs 4 EGT probes, one for each cylinder.

yeah, but he's using an innovate datalogger.

I know i just figure that someone using information from four EGT probes, even with the LM datalogger assembly might relate to some useful experiences with the EGT logging ability.

I don't really see the point, will your EGTs not be of appropriate level if your timing and fuel is tuned for optimal horsepower considering at that point you'll have optimum burn?
I really don't know myself.

The folks I know doing it tune first fuel with AFR's then watch EGT's and tune till the EGT's are getting out of the safe range so they know how much advance to run. Obviously no one wants to feed their pistons/valves to the turbo.

And I'd love to just be able to 'look at it later'.

Do you know what that chip does? Can you run two EGT's? I don't have two, but I'm curious. :-)

I'm surprised you feel that way.

knowing of the EGT's are too high when at WOT will allow you to advance the timing and stop burning you valves up and prematurely killing your engine.

IMO knowing the EGT's not quite on a level of knowing the AFR's but not far off. it's certanly an invaluable tuning tool.

(that said I've still to build my circuit...... )

car was tuned on a dyno
my egt probe only goes to 1600.
it's cool, but not that useful.

yeah I suppose it's more useful if you're road tuning.

Ben, when you say "only goes to" do you mean you run higher egt than 1600?

not while cruising, but under boost 1500F+ isn't hard to do.
cruising on the highway at 80mph indicated is around 1400F.

yeah - my buddie's diesel is supposed to burn the turbo at 1650* and he runs 1610, with a guage that only reads to 1650. Yipes! To me I'd want a little head room there, I just can't trust something right at the top of it's range.

I've heard Miatas are good to around 2k? Probably wrong though. I see around 1550-1600 on-track.

Good answers. Sounds like its a Go for building the circuit.

Pieced together the parts order from digikey and that little IC is pretty expensive for what it is... 20 bux!

No clue what it does, and don't even remember how thermistors even work.. I think it goes on voltage but I could be wrong? Unfortunately I'm not a circuit designer, just a builder. :(

Does anyone know what optimal EGT ranges are? I know there are a lot of variables, but just a rough guess? Is 2000 the total limit before destruction? Whats optimal with a good tune? Part of the problem is I lack theory on relevance of EGT to the tune itself. I understand that high egts are a bad thing, but was always told a high EGT is a result of a lean mixture under heavy load?

Curious.. What kind of load is that on the engine and whats your boost reading at an 80mph cruise reading 1400?

It's a thermocouple, not a thermister - there's a temperature dependant voltage for any two disimilar metals specially joined (welded). It's VERY small currents, and so you need sensitive equipment to measure it. Technically, you want to run the same wire type from the sensor all the way to the readout, good readout equipment will have the same metal all througout it - the type of metal depends on the thermocouple type - most often in automotive use you find "K-type" wires.

As far as temps, I'm not sure! I've heard so many different numbers I'm always afraid to say. I think 1800 is on the high side, I wouldn't go to 2k unless you verify it's ok! Once fuel is right, move timing till you get optimal temps, that much I know. :-)

(What's weird: For GOOD thermocouple reading, you typically need a second one, attached to a thermister. They are easier to characterize, and are used to correct the meter. I'm not sure if this IC you have has one integrated (but I doubt it, I've never seen it before) but it could lead to errors. Real, lab-grade thermocouples are stuffed full of more thermocouples to ensure they read their channels correctly.

I bought an EGT gauge as an "oh shit" indicator.

That sounds familiar. My brothers company builds and calibrates lab grade testing equipment and they have used Fluke single channel thermocouple and meter for sale.. I commented that I would likely have bought it if the unit had two inputs. Was interested in intercooler in, and intercooler out temps, though actually I only really need the inlet because I have the MAT sensor.. Thats besides the point. He explained in laymen how they work.. was still a little bit over my head. :) Only thing I do remember him saying is what you mentioned about same wire from end to meter for best results.

I don't think this is really rocket science, really.. just need a "close enough" recording.

haha. I don't need anything more to scare me, this project has more than enough things!

Yeah - as long as you're ok being 1.5 margin-of-errors away from the edge. If your pistons melt at 1600, and your guage is only accurate to +/- 50*, then you can't go beyond an indicated 1550. And since it's +/-50*, you might actually be running 1500* but still back off to be safe.

But yeah - there's a point where it's not worth worrying about. I wonder how hard it is to build a corrected circuit, or maybe that chip already does it.

You could switch back and forth. At work we have an old reader with two inputs, it's pretty nice. Also, if you're in a narrow-ish range and you don't care about accuracy so much, thermisters are easy to read (just a resistance).

I dunno about you, but my car has a OEM temp sensor in it. I could probably move it to the other side of the turbo.

I guess I would search on thermocouple multiplexers. If that's easy, one readout could read them all, and you could litter your motor with them. Put one in your passanger seat to see if you're impressing any female passengers, or getting male ones to wet themselves.

-----
in the past, I've used thermos to calibrate my temp guage and similar stuff, they are so small you can slip them under most hoses. I have a single channel readout from some old job that closed down. Some of the better fluke meters will also read thermocouples.

what does an escort GT have to do with megasquirt? LOL

As Abe said, thermocouples have nothing to do with thermistors. Thermocouples are based on the Seebeck effect, where joints of discrete, different metals create a voltage differential between the two metals, on what is called "the hot junction" (where the two metals join and the temperature is measured). The voltage is very small - 0V for 0*C (32*F) and just 4mV for 100*C (212*F), non linear. Typical metals used are Iron-Constantan for type J and Chromel-Alumel for type K. Type J can only read up to 750*C; type K can go up to 1250*C.

The purpose of the AD595CQ chip is to AMPLIFY this voltage, to a measurable magnitude - about 10mV per 1*C and it does so linearly: 0C = 0V, 1200*C = 12V (2192F). You then use a simple 1/2 voltage divider (10K/10K) to scale this to 0C=0V, 1200*C=6V, which means that 1000*C=5V (remember that it is linear).

I have found that most modern gauges lack Cold Junction Compensation. The cold junction is where the two metals join on your circuit (yes, they do join internally on the circuit). The voltage measured at the ends of the thermocouple wire is not only dependant of the temperature of the probe (hot junction) but also of the temperature at the circuit end of the wires (ie where you connect the wires to the circuit) - the cold junction.

For a reliable measurement there MUST be Cold Junction Compensation. If your gauge does NOT include CJC, when your cabin is still cold in the winter (say 5C/40*F) and then you turn on the heater and after 5 mins, the temperature of the gauge (which is very near the heater core and hoses) reaches 50-60*C, you are experiencing a drift error of up to that temperature differential. With an AD595CQ, if you make sure that the temperature of the cold junction (where you solder your wires or connectors on the PCB) is the same as the temperature of the AD595CQ chip, you are golden.[1][2] Just make sure that you solder/connect the wires as near to the AD595 chip as possible and NEVER use any different wires/connectors to extend the thermocouple wire. Only use special type K wires and connectors.

Jim

[1] There is a drift error on the AD595CQ chip as well, as the CJ temperature (ie PCB temperature) drifts from the ideal 25*C: +/- 0.6*C output error per 25*C of difference, which is really insignificant for our type of applications.

[2] The AD595CQ also uses an internal ice-point (0*C) reference for proper measurement which is calibrated during the manufacturing stages and this one of the reasons why the AD595CQ is pretty expensive for what it is.

It all depends on where your probe is. My application is naturally aspirated and I easily see temps of up to 850*C (1600*F). Friends with Greddy turbos see up to 1400-1450*F. I have the probe about 1.5" away from the head; they have the probe about 2" away from the turbo, which acts a huge heatsink (remember that the purpose of the turbo is to absorb the energy of the exhaust gas - kinetic energy and heat which is in fact tiny kinetic energy in the nanoworld), so the temps AFTER the turbo are guaranteed to be lower than before the turbo. Depending on the size of the turbo as well as several other parameters, I expect to see 100-150*C of lower EGT after the turbo (ie: 950*C before, 800*C after).

Jim

First of all; a big:bigtu: to elesjuan for starting this thread and to all previous posters for contributing. I repeat what I've said before; you young guys never cease to amaze me! This kind of thread is what separates you from other forums.

Now, on to my question to reverant; Jim, my question is: why AFTER the turbo? If I read your post correctly, temperatures before the turbo would be higher. And back to a question already asked: what would be the ideal (?) temperature anyone should shoot for?

I come from an era when there were no EMSs in the cars and tuners would always tune based on EGTs but I never found a tuner that could give me a solid answer. The closest was to tell me to watch out not to go over 1600 degrees

Thanks,

Rafa

BTW, MERRY CHRISTMAS TO ALL!

Best to have the probe before the turbo. You want to measure "Exhaust Gas Temperature" before it is modified by the turbo and its' heatsink properties.

Ok, got it; never had a turbo car before. Still, what is the best EGT range anyone should shoot for?

I found this interesting:

http://www.sdsefi.com/techegt.htm

^ link = :bowdown::bowdown::bowdown:

olderguy thanks for posting that was a good read

Nice bit of information there! Well, it wouldn't be hard to run thermocouple line out of the MS and leave a connector dangling. Then your junction could be the pin of the IC, hard to imagine a big offset there.

I'm definately going to do this soon...

Wow man! Thats probably the single most impressive piece of information I've ever read on something technical like this. :eek: :bowdown:

Thank you very much for the info!

I do have a quasi-related thermodynamic question about turbochargers and myths of heat..

Given that an engine is turbocharged and in moderate tune to produce a good amount of power, lets say for example the temps right outside the exhaust ports are around 1500*. What differential would you say that is from the actual combustion CHAMBER vs. the probe measurement? The cylinder heads are aluminum which remove heat from the combustion pretty well, pistons are aluminum and oil cooled, plus the valves (which I wouldn't factor much cooling properties from the steel valves just wanted to mention them.) Adding on the turbo manifold which is cast iron in my case, plus the turbocharger which is cast iron. Turbos by design are mufflers and heat sinks, they use thermal energy along with gas / air flow to spin the turbine.

Taking that information into consideration, are there really benefits from adding thermal or ceramic coatings to Pistons, Manifolds, and turbine housings? Do these benefits contribute more to keeping say, my brake master cylinder from melting or the efficiency of the engines combustion process? I've heard old myths before that "header wrap" especially on high heat applications ie. turbochargers will actually cause the materials wrapped in to physically fatigue?


So if I bought one of the K-type units I found from the other thread I need to find more K-type wire and the connectors all the way to the PCB where the AD595 chip is soldered on? That board will be inside the megasquirt case, I mounted a small expansion PCB to the inside of the cover for small circuits like this.

You can't readily associate the exhaust gas temperature with the chamber temperature. Let's assume for a moment that the exhaust gas is homegenous, ie all the gas has the same temperature. Which point in the combustion chamber are you interested in measuring? Piston top? Crown? Skirt? Ring land? Cylinder walls? (where and which cylinder?) Valves? There are a myriad locations and rest assured that each one will have different temperatures depending on the flow of coolant as well (is there a coolant jacket near the measurement point?)

If you need to be able to disconnect the sensor from the MS PCB, you need K-type connectors:

http://export.farnell.com/jsp/Connec...sp?sku=8598282
http://export.farnell.com/jsp/Connec...sp?sku=3810628

Jim

Reverant is right, in that you're getting sort of course information here.... But, there's some interesting caveats, you might at first think it's obvious the cylinder is hotter than the gas, but it's the gas doing the heating, if it's not in the chamber long enough, the chamber won't necessarily get to the temperature of the gas (theoretically it can't) not to mention there's boundary layer issues: On broad, flat surfaces gas doesn't really "scrape" the surfaces - the whole thing about how your car can stay dirty driving at 100 mph, the boundary layer keeps the moving air from "touching" the surface of your car.
Anyway, I've heard the metal in the chamber is often colder than the gas coming out - and I assume since the egt probe is "sharp" it does a better job of measuring the temps of the flowing air.

The links didn't work to the parts, but the idea is nice! Beats soldering to the board!

The earlier link was odd - mostly I have heard what it said before - the tuning systems they sell are a bit simplistic, and it seemed to be dumbed down just a bit? Anyway, I'm learning stuff, keep it coming. :-)

Abe: I sifted through that link Reverant posted and found the parts he was trying to post. Javascript on the page makes links hard to post on a forum.

http://export.farnell.com/productima...d/42420793.jpg
http://export.farnell.com/productima...d/42419341.jpg

Went to the root page http://www.farnell.com clicked on United States, Connectors, industrial, Thermocouples.

Good find!! They're not too expensive from there either.

Even found this on there! http://export.farnell.com/productima...9818504-40.jpg

http://www.egauges.com/vdo_indS.asp?...ad&PN=R660-6PL

Place in the states, I think thats acceptable wire for a thermocouple using one of their sensors like this one: http://www.egauges.com/vdo_indS.asp?...1_5&PN=R650SPL

Add those K-type plugs for the megasquirt case and you're golden!

k-type in green? That's just weird. Green is... I forget, not k type. Purple is t, J is brown? I don't remember.

Anyway, if it's labled k, it's probably right. And yeah, adding them in the case would be great. It's on my short list of must-do's

I think I still like the probe I got better, very exposed tip, must be pretty fast. Then again, you can get even more exposed so.... It's always a trade off.

One thing left to find... According to Reverant the wires from the Case plug to the board need to be thermocouple wire also? Where would one find say 6" of that type of wire, or will regular copper work in that position?

You should keep the same metal as far along as you can - you could get a thermocouple passthrough, which will work great but be pricey. Personally, I'll probably just use a pigtail, or mount the board right near the edge so the thermo standard connector can plug in through the side. The trouble with changing wires outside the box is there's more likely to be different temps inside the box than outside.

Okay I think I have a good solution.

I'll cut a small notch in the endplate of the case to run the cable through inside then mount one of the K-type sockets directly to the board. That way the sensor plugs into the harness cable, then that cable plugs into the circuit board but can be disconnected easily. Hopefully that'll work.

Green is K-Type in the UK (imperial) while it is yellow in the US. Chromel/Alumel (+/-) cables are respectively Green/White in the UK while Yellow/Red in the US.

Jim

The plug I posted is PCB-type, which means that you solder the connector to the board. If you want a connector that you can attach to the case, then cut some wire from the thermocouple sensor's own wire.

COPPER WILL NOT DO!!

Jim

The place I posted sells the sensor, with connectors, and the cable by the foot as well.

Maybe it didn't make it into this thread.

http://www.teamrip.com/accessories.html

pics of my probe:
http://abefm.smugmug.com/gallery/4022112#234090908

Oh, the guy is terrible with email, etc - the parts came, just after I started to worry they wouldn't. Effectively, it was fine - pay and nice parts come. But don't expect to start a conversation with the guy.

If anyone's looking for open-element ones, I have a friend who found some cheap. Might be worth checking into, though they don't last long. If I were going to bother running 4 sensors (hint to no one in particular) wouldn't it be worth having them FAST?

oh you dirty bastard.. walkin round, showin your probe on a public forum..

:D

Thanks for the linkage.