Will this work for EGT probe? - PeachParts Mercedes-Benz Forum

300SD81 · #1 07-01-2008, 06:29 PM

Ran across this while looking for something else, I'm wondering if it can be used as an EGT probe...

They're only $10 shipped, and I don't mind using my multimeter (includes K-type thermocouple)...

bgkast · #2 07-01-2008, 06:50 PM

It could work, but you wound need to calibrate it. X ohms of resistance on your multi-meter won't mean much otherwise.

300SD81 · #3 07-01-2008, 07:00 PM

That one is a type-K thermocouple, and my multimeter has a built in type-K thermocouple, so theres no calibration involved. Thermocouples generate voltage, not current. I'm working on a circuit that uses a MAX6675 and a microcontroller to interface it to USB now (all parts where free samples

)...

I'm just wondering whether the probe is long enough to give an accurate EGT and not a exhaust manifold temp...

Jeremy5848 · #4 07-01-2008, 07:08 PM

That should work. I don't know whether the exhaust manifold on your engine has any available tapped holes; in any case, you would have to re-tap to use the 1/4 inch thread of the thermocouple.

For best results, the thermocouple must be out in the exhaust stream. The EGT probe in my '85 300D-T was initially used with an adapter that kept most of the probe in the metal of the fittings and the manifold and consequently read on the low side (max about 800F). The "upgraded" version uses a shorter fitting and, when installed in my '87 300D Turbo, should read more accurately.

Jeremy

bgkast · #5 07-01-2008, 07:26 PM

Quote:

Originally Posted by 300SD81

That one is a type-K thermocouple, and my multimeter has a built in type-K thermocouple, so theres no calibration involved. Thermocouples generate voltage, not current.

It sounds like it will work fine then.

I think thermocouples produce resistance

Cervan · #6 07-01-2008, 07:27 PM

For the price of 10$ you could get five of them for each exhaust port and then average them on a single display.

lutzTD · #7 07-01-2008, 07:27 PM

Quote:

Originally Posted by 300SD81

Ran across this while looking for something else, I'm wondering if it can be used as an EGT probe...

They're only $10 shipped, and I don't mind using my multimeter (includes K-type thermocouple)...

wow let us know, thats a great price. Most likely the guages are calibrated for K type as well. I dont thnk J types work well at higher temps.

300SD81 · #8 07-01-2008, 07:32 PM

Theres a ton of them on ebay if you guys are interested...

http://search.ebay.com/search/search.dll?sofocus=bs&sbrftog=1&dfsp=32&catref=C6&from=R40&satitle=K+Type+Thermocouple+Temperature+Probe&sacat=-1%26catref%3DC6&sargn=-1%26saslc%3D2&sadis=200&fpos=ZIP%2FPostal&sabfmts=1&ftrt=1&ftrv=1&saprclo=&saprchi=&fsop=32%26fsoo%3D2&coaction=compare&copagenum=1&coentrypage=search

I'm starting to doubt that these will work for EGT, the probe is only 1/2in long, too far out of the exhaust stream. But why are EGT probes so much more expensive?..Its basically the same construction, just with a longer probe..

300SD81 · #9 07-01-2008, 07:41 PM

Quote:

Originally Posted by bgkast

It sounds like it will work fine then.

I think thermocouples produce resistance

I'm pretty sure its voltage,

http://www.azom.com/details.asp?ArticleID=1208#_How_They_Work

Thermistors are the ones with varying resistance.

lutzTD · #10 07-01-2008, 08:34 PM

Quote:

Originally Posted by 300SD81

Theres a ton of them on ebay if you guys are interested...

http://search.ebay.com/search/search.dll?sofocus=bs&sbrftog=1&dfsp=32&catref=C6&from=R40&satitle=K+Type+Thermocouple+Temperature+Probe&sacat=-1%26catref%3DC6&sargn=-1%26saslc%3D2&sadis=200&fpos=ZIP%2FPostal&sabfmts=1&ftrt=1&ftrv=1&saprclo=&saprchi=&fsop=32%26fsoo%3D2&coaction=compare&copagenum=1&coentrypage=search

I'm starting to doubt that these will work for EGT, the probe is only 1/2in long, too far out of the exhaust stream. But why are EGT probes so much more expensive?..Its basically the same construction, just with a longer probe..

seems like it should be plenty long enough. the walls onthe manifold arent that thick. just try to put it on the outside wall of a turn and the boundary layer there should be pretty thin.

Tymbrymi · #11 07-02-2008, 10:12 AM

Quote:

Originally Posted by 300SD81

That one is a type-K thermocouple, and my multimeter has a built in type-K thermocouple, so theres no calibration involved. Thermocouples generate voltage, not current. I'm working on a circuit that uses a MAX6675 and a microcontroller to interface it to USB now (all parts where free samples

)...

That MAX6675 chip is a good one. A friend used it in his senior design project and it was easy to setup and worked flawlessly.

What micro do you plan on using? And why the USB? Connecting it to a laptop for a display? If you'd like a quick and dirty way to talk to the outside world without the hassle of USB software on the PC check out FTDI FT232R. I've never used USB other than that, so it might be really easy... I just haven't played with it yet so have no idea.

An EGT probe you may want to try is this one . Some folks on the VW forum have had good luck with them, and they are fairly cheap as well.

Keep us posted!

Bajaman · #12 07-02-2008, 10:22 AM

I think that with that you will be measuring the temperature of the manifold more that the exhaust. If you look at a proper EGT thermocouple, they extend at least to the center of the flow. What you have is right on the edge, and its likely that it will not give you a true measure of EGT.

bgkast · #13 07-02-2008, 11:04 AM

That thermocouple looks like it measures from the tip which should extend plenty into the exhaust stream for a good reading.

300SD81 · #14 07-03-2008, 04:44 PM

Quote:

Originally Posted by Tymbrymi

That MAX6675 chip is a good one. A friend used it in his senior design project and it was easy to setup and worked flawlessly.

What micro do you plan on using? And why the USB? Connecting it to a laptop for a display? If you'd like a quick and dirty way to talk to the outside world without the hassle of USB software on the PC check out FTDI FT232R. I've never used USB other than that, so it might be really easy... I just haven't played with it yet so have no idea.

An EGT probe you may want to try is this one . Some folks on the VW forum have had good luck with them, and they are fairly cheap as well.

Keep us posted!

I'm using a Microchip PIC18F4553, it has a built in USB serial port device that can be accessed easily from C code. I'm making a Car PC out of parts of a broken media center PC (mini-ITX) I got for free. The screen is going to be mounted in a hollowed out sun visor and heres a preview of the display I'm working on...

If I can find a good way to read a thermistor and calculate out the extreme non-linearity, I'll be making one for oil and tranny temp, and I'll probably be making ones for oil/tranny pressures too, using these things makes adding gauges so cheap, I can't believe noones thought of it before... The only parts I can't get as free samples or junkyard parts are the circuit board and thermocouple, the rest is in software...

Tymbrymi · #15 07-04-2008, 07:38 PM

Quote:

Originally Posted by 300SD81

I'm using a Microchip PIC18F4553, it has a built in USB serial port device that can be accessed easily from C code. I'm making a Car PC out of parts of a broken media center PC (mini-ITX) I got for free. The screen is going to be mounted in a hollowed out sun visor and heres a preview of the display I'm working on...

Very nice looking display!! What language/toolkit did you use to program it? My GUI programming is limited to Java, and a little bit of Microsoft MFC. Neither of which would easily display that on their own!

Quote:

Originally Posted by 300SD81

If I can find a good way to read a thermistor and calculate out the extreme non-linearity, I'll be making one for oil and tranny temp, and I'll probably be making ones for oil/tranny pressures too, using these things makes adding gauges so cheap, I can't believe noones thought of it before... The only parts I can't get as free samples or junkyard parts are the circuit board and thermocouple, the rest is in software...

Besides the price, why not just use thermocouples?

If you're looking for PCB mfgrs.. I know of two good ones.

http://www.pcbfabexpress.com/
http://www.4pcb.com/

PCB Fab Express used to be a lot better than they are now... its been about two years since I've used them.

G'luck and let me know if you need anything

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