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CHTs everywhere

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rampil

Joined: 04 May 2007
Posts: 870

Posted: Wed Apr 09, 2008 4:49 am Post subject: CHTs everywhere

I finally completed my cylinder head temp monitoring system so now

I have 3 sites of measurement: Regular Rotax VDO probes into

the heads of Cylinders 2, 3 going to an analog gauge;

 Ring-type CHTs installed under the Rotax CHT probes and monitored by

my Blue Mountain EFIS, and finally the Lockwood/Rotax coolant temp

probe with a Blue Mountain probe going into the EFIS.



So far, I have only done cowl-off, static testing but the results are

interesting:  

The coolant temp at 4000 rpm is 20F higher than the Rotax/VDO

which is about 20F higher than the ring probes outside the block.



These will probably change when cowled and at cruise and climb which

I plan to test when I return from SnF.

_________________
Ira N224XS

sidsel.svein(at)oslo.onli
Guest

Posted: Wed Apr 09, 2008 9:33 am Post subject: CHTs everywhere

Ira,



 	  Quote: 	
		  - - - - - - -  the Rotax/VDO

 which is about 20F higher than the ring probes outside the block.


	


I do not have the Rotax/VDO probes into the block, only ring probes fitted 

with a bolt into the original probe holes.  I found that the ring probes in 

flight were cooled considerably by the air flowing in under the cowling.  I 

smeared a generous amount of heat resistant (red) Loctite silicone sealant 

all around the area.  This appears to have effectively insulated the rign 

probes from direct air cooling.



Regards,

Svein

LN-SKJ

rampil

Joined: 04 May 2007
Posts: 870

Posted: Wed Apr 09, 2008 12:03 pm Post subject: Re: CHTs everywhere

Hi Svein!



I suspect the same!.  After I get back from Lakeland, I will try to rig

some sort of insulating surround for the probes.  A little fire-stop

caulk or hi-temp silicone may be just the ticket as you have done.

I'll let you know.

Cheers!



Ira

_________________
Ira N224XS

hurstkr(at)redzone.com.au
Guest

Posted: Thu Apr 10, 2008 1:27 am Post subject: CHTs everywhere

Hello Ira,



I've yet to get to this exciting stage but I'm just wondering if you have 

calibrated all the sensors and their respective monitors by putting all the 

sensors in a pot of cold water and then bringing it all to boiling point to 

ascertain any discrepancies which might exist in these items alone ?



Best regards

Kingsley in Oz.



---

josok-e(at)ukolo.fi
Guest

Posted: Thu Apr 10, 2008 3:18 am Post subject: CHTs everywhere

Interesting data!

On my bird there are ring probes under the spark plugs, and one Rotax cht probe is in use. The ring probe on #3 indicates about 15 C higher as the Rotax probe. Since oil- and coolant temperature are coupled in the oi-water heat exchanger, i am using the oil temperature as coolant temperature indication. All the temperatures are within 1 degree when the engine is cold. If the engine pre-heater is on and the cowl under it's blanket, all temperatures are again within 1 degree of about 50 C. 

My concern is in flight, especially on low power, like 55%, the front ring terminals are around 60 C, and the hottest rear is around 100, with 95 C for the other. Oil will typically be 85 to 90 C That's with an OAT of -5 to -10 C. My next move is to temporarily block the standard air cooling openings and see if the Rotax shroud and it's intake will produce a more even picture. And then hope for acceptable results in the hot summer. 



Regards,



Jos Okhuijsen

Visit -  www.EuropaOwners.org

europa(at)pstewart.f2s.co
Guest

Posted: Thu Apr 10, 2008 3:26 am Post subject: CHTs everywhere

Ira



Are you not monitoring the VDO probes with your EFIS because they are  

ungrounded probes?



I am hoping that changing the VDO probes to Westach grounded  

alternatives (which fit the holes in the head) will work. They  

certainly read on the EFIS but we haven't had the engine running yet.



regards



Paul

On 9 Apr 2008, at 13:49, rampil wrote:



 	  Quote: 	
		   



 I finally completed my cylinder head temp monitoring system so now

 I have 3 sites of measurement: Regular Rotax VDO probes into

 the heads of Cylinders 2, 3 going to an analog gauge;

  Ring-type CHTs installed under the Rotax CHT probes and monitored by

 my Blue Mountain EFIS, and finally the Lockwood/Rotax coolant temp

 probe with a Blue Mountain probe going into the EFIS.



 So far, I have only done cowl-off, static testing but the results are

 interesting:

 The coolant temp at 4000 rpm is 20F higher than the Rotax/VDO

 which is about 20F higher than the ring probes outside the block.



 These will probably change when cowled and at cruise and climb which

 I plan to test when I return from SnF.



 --------

 Ira N224XS





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=175679#175679

rampil

Joined: 04 May 2007
Posts: 870

Posted: Thu Apr 10, 2008 4:02 am Post subject: Re: CHTs everywhere

Hi Kingsley,



Be a former quant, yes, I love calibration! In situ the probes all read equal

when the engine is cold.



Hi Jos,

It would be very interesting to compare the ring location I have vs the 

spark plug site.  I was advised by Kerry at Lockwood not to go there

because the relationship between temps there and the "official" site

were not known or at least documented.  I am enclosing a pic of the 

two probes installed.   When using the VDO probes on 2,3 on my old

BMA EFIS, there was usually a 20F delta between front and back. The

shroud should certainly help but it is very expensive.  Homebrew anyone?

Hi Paul,

You are correct!  The unipolar probes will not work at all. By design of the

engine pod, the voltage across the temp sensitive resistor is not

ground referenced and grounding the bottom of the resistor will

screw the constant current injector driving the probe.  Greg and I tried

it anyway to see if it might work, but it was No Go.



I would suspect that Westach probes will not work. Blue Mountain does

not publish the sensor specs or cal curves but they use a UMA oem

sensor element.  If you are using a Gen4 unit, you as a user can not

recalibrate to a different sensor.  If you are using a previous generation

EFIS, anything can be made to work but you will need to calibrate it.

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_________________
Ira N224XS

josok-e(at)ukolo.fi
Guest

Posted: Thu Apr 10, 2008 4:06 am Post subject: CHTs everywhere

Paul,



The Rotax cht probes are grounded, one side, the housing is ground, and the other side is the connector. They are of the PTCor NTC  type, that is a resistor, which changes it's resistance with temperature. Other types of probes are thermocouples, usually designated as "J" or "K" type probes, which produce a tiny voltage depending on the temperature of the junction. Those can be grounded or not. Whether you need resistive probes or "J" or "K" types probes is dependent on the EIS and it's inputs. My Dynon D180 accepts both, but only on certain positions.



Regards,



Jos Okhuijsen

Visit -  www.EuropaOwners.org

europa(at)pstewart.f2s.co
Guest

Posted: Thu Apr 10, 2008 7:08 am Post subject: CHTs everywhere

Jos

It's using aircraft ground which a believe is the problem with the  

BMA EFIS - hence the need to use a thermistor with two wires. I  

believe the E1 uses it's own internal ground as reference so CHT and  

Oli temp need grounds going back to a ground pin on the EFIS.



At the risk of upsetting Ira, and accepting I have very little  

expertise in the area, I wouldn't buy the Blue Mountain unit again.  

Not for a Rotax anyway and not flying in Europe. Still you live and  

learn.



Regards



Paul

G-GIDY

On 10 Apr 2008, at 13:04, josok wrote:



 	  Quote: 	
		   



 Paul,



 The Rotax cht probes are grounded, one side, the housing is ground,  

 and the other side is the connector. They are of the PTCor NTC   

 type, that is a resistor, which changes it's resistance with  

 temperature. Other types of probes are thermocouples, usually  

 designated as "J" or "K" type probes, which produce a tiny voltage  

 depending on the temperature of the junction. Those can be grounded  

 or not. Whether you need resistive probes or "J" or "K" types  

 probes is dependent on the EIS and it's inputs. My Dynon D180  

 accepts both, but only on certain positions.



 Regards,



 Jos Okhuijsen

 Visit -  www.EuropaOwners.org

josok-e(at)ukolo.fi
Guest

Posted: Thu Apr 10, 2008 10:09 am Post subject: CHTs everywhere

Hi Ira,



Because there is no factory data available for under spark plug temperatures, i did compare those with the original Rotax probes in head 1 and 3, and came to the 15 C higher outcome under normal loads. The spark plug sensors react much faster then the rotax probes, which can be expected, thermocouples have a much lower lag. The main reason for going this way however was to have an early warning available in case one of the barrels goes out of the normal. This, together with 4 EGT probes gives a pretty good picture on what's going on. I did go the expensive way, Rotax shroud. Which function is pretty much inhibited by the standard openings as i am experiencing now. I will come back and report on the next, closed eyes experiment. After all, this is an experimental!



Regards,



Jos Okhuijsen

Visit -  www.EuropaOwners.org

josok-e(at)ukolo.fi
Guest

Posted: Thu Apr 10, 2008 11:07 am Post subject: CHTs everywhere

Paul, 

While i don't really want to be knit-picking, i don't quite understand why or where the engine ground would differ from internal ground. Unless there is a bad connection somewhere in between. However unlike thermocouples, there are many different characteristics for resistance probes. It may very well be that BMA thinks it's too much trouble to cope for Rotax probes in software. We'll certainly manage to upset Ira!



Regards,



Jos Okhuijsen

Visit -  www.EuropaOwners.org

europa(at)pstewart.f2s.co
Guest

Posted: Fri Apr 11, 2008 3:46 am Post subject: CHTs everywhere

Jos



What I think happens is that 12v into the EFIS goes through a DC/DC  

converter which isolates it from a/c ground and sets its own internal  

reference (this was how it was explained to me by Jim Butcher).



My comment about the BMA unit was merely that for the less able it is  

a complex unit to set up for the Rotax. It's clear from the BMA  

discussion board that there are many owners who understand and enjoy  

its flexibility (and complexity). When we bought we were not  

anticipating having to swap out engine sensors or being unable to use  

the Rotax tacho output - we hoped for more of a 'plug and play'.



Still when it flies maybe all will be forgotten.



Regards



Paul

On 10 Apr 2008, at 20:03, josok wrote:



 	  Quote: 	
		   



 Paul,

 While i don't really want to be knit-picking, i don't quite  

 understand why or where the engine ground would differ from  

 internal ground. Unless there is a bad connection somewhere in  

 between. However unlike thermocouples, there are many different  

 characteristics for resistance probes. It may very well be that BMA  

 thinks it's too much trouble to cope for Rotax probes in software.  

 We'll certainly manage to upset Ira!



 Regards,



 Jos Okhuijsen

 Visit -  www.EuropaOwners.org

rampil

Joined: 04 May 2007
Posts: 870

Posted: Fri Apr 11, 2008 4:06 am Post subject: Re: CHTs everywhere

Hi All,



I'm not upset --- I'm at Sun & Fun!



The Engine ground is technically suboptimal as a path for small signals

like the millivolts of a T/C or a small resistance probe 200-240 ohms

because it has a lot of electrical noise on it. For example,

the spark plus return their kilovolt jolt through it, etc. Any tiny resistance

will make very big voltages from the sparks.



The Gen4 Blue Mountains are completely simple to hook up. No more

understanding of electronics is required. You use their probes and it

is set - no cal, no programming, easier than most of the competition.

_________________
Ira N224XS

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