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JPI vs EI

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Discover

Joined: 26 Feb 2007
Posts: 429

Posted: Wed Mar 25, 2009 8:14 am Post subject: JPI vs EI

Gary,

 I thought this an interesting thread on the  GG.

 I understand that the JPI probes are grounded  while the EI are not.

 Is it possible that this accounts for th  edifferences in your thorough comparison tests?

 ned

  

  

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GrummanDude

Joined: 15 Jan 2006
Posts: 926
Location: Auburn, CA

Posted: Thu Mar 26, 2009 12:20 am Post subject: JPI vs EI

Dave doesn't know what he's doing. Â I always add the ground and it's still a lot higher.

 

 

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Gary
AuCountry Aviation
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GrummanDude

Joined: 15 Jan 2006
Posts: 926
Location: Auburn, CA

Posted: Thu Mar 26, 2009 12:35 am Post subject: JPI vs EI

I flew with both the EI and JPI installed in my plane for over a year and over 25 flights. Â I had the EI in #3. Â Based on over 300 hours on previous flights over the previous 3 years, I know the #3 should be within 10 degrees of #4. Â  

 

  I tried to explain this the best I could in a write-up in the Star. Â 

  

 

  â€œFor those who believe, no proof is necessary. For those who don't believe, no proof is possible.â€Â Â - Stuart Chase

 

 

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Gary
AuCountry Aviation
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flyv35b(at)minetfiber.com
Guest

Posted: Thu Mar 26, 2009 5:13 am Post subject: JPI vs EI

So if there is the large variation that you say  between EI and JPI, which one is accurate or the most accurate? And why?   Apparently you don't feel that grounding problems are or can be an issue.   Which system did you use for your cowling cooling tests?

  

  

 Cliff

 [quote]   ---

cloudvalley(at)comcast.ne
Guest

Posted: Thu Mar 26, 2009 5:36 am Post subject: JPI vs EI

Hi Cliff, 

 Do you like JPI better? 

Brian 

---

flyv35b(at)minetfiber.com
Guest

Posted: Thu Mar 26, 2009 6:38 am Post subject: JPI vs EI

Not really.  As a company and from a product  support standpoint I think EI is far superior.  EI also makes all of their  own probes, transducer and instruments.  As far as I know JPI doesn't make  anything (themselves).  Having said that I have both instruments in my two  planes and both have been satisfactory.

  

 Cliff

 [quote]   ---

Discover

Joined: 26 Feb 2007
Posts: 429

Posted: Thu Mar 26, 2009 10:02 am Post subject: JPI vs EI

Gary,

 Good enough for me!

 I've read your Star article and thought you  did an excellent job writing it and researching it. I've had an ongoing argument  with another GG'er for over a year defending your work to him. I like your  Stuart Chase quote and think it really does have a lot of merit in all kinds of  situations......unfortionatley, so many people are unable to alter their  beliefs in the face of the facts. Their presuppositions are more important  to them sometimes than reality even with the facts clear  presented.....

 ned

 [quote]   ---

GrummanDude

Joined: 15 Jan 2006
Posts: 926
Location: Auburn, CA

Posted: Thu Mar 26, 2009 11:52 am Post subject: JPI vs EI

If you turn on a soldering iron and touch the tip with a thermometer (thermal couple) you'll get one reading. Â If you move it away from the soldering iron 1/8 of an inch, you'll get another. Â The JPI probes touch the cylinder head. Â The EI probes sit in the well, heated by the surrounding aluminum. Â They are measuring different things. Â 

  

 

 It isn't a question of which one is accurate. Â I would bet that both are within 1 degree of being accurate. Â Do a little research on thermal couples and you'll find that thermal couples come in all configurations. Â Some require grounding, some don't. Â Do I want a system that uses a floating ground (EI)? Â No. 

 

  I forget a lot from my engineering classes regarding thermal couples, but, as I recall, someÂ thermal couples are used as a source voltage themselves in a circuit and otherÂ thermal couples are used is a powered circuit requiring a common source ground. Â 

 

  

 

  As for which one is better, personally, the JPI makes for a much cleaner installation. Â I think the JPI looks more professional and the operating logic is more what I would expect; i.e., less of a learning curve. Â The wires are a lot easier to route and you can cut them to length instead of wrapping up and tying up large bundles of wiring. Â Quite often, on EI installations, the wire gets bundled up under the instrument panel in large wads of wiring. Â Looks l ike shit, but, I guess no one but me cares about what the backside of instrument panel looks like (based on what I see in everything I work on). Â [Note: Â I wish you all could see behind the panelÂ of 26392. Â You'd swear there were no wires at all.] Â The JPI has more features for the same money. Â As for customer service, there have been big changes in the last 3 or 4 years regarding service. Â The warranty is actually better than published. Â The JPI EDM 800 in my plane, since 2004, began displaying weird number flashing on occasion last year. Â I sent it in and they fixed it at no cost. Â I did this with another customers plane with a display that was dim (it was also 3 years out of warrantee). Â No cost. Â Other than those two, I haven't had to send a JPI back for service in the 10 years I've been installing them.

  

 

  The question was: Â What system did I use in the FAA portion of the flight testing? Â  EI of course. Â I wanted to get the lowest CHTs possible. Â Besides, the DER already had a certified EI system. Â Running all that shielded wiring, 14 of them, through the ADF hole in the floor of the plane, was interesting. Â I could have run twice that number of JPI wires through the same opening. Â 

  

 

  The question should be: Â What did I find with the JPI set-up in my plane? Â and, what did I find with the JPI set up in the flight test airplane. C2

  

 

  BY-THE-WAY: Â It's trivial to remove a JPI CHT probe. Â The wiring isn't fixed to the nut used to tighten the probe into the cylinder head. Â The JPI uses a separate shell to tighten the probe in place. Â THUS: Â a JPI CHT probe can be removed with the cowling in place in about 1/10 the time it takes to remove an EI probe, WITHOUT REMOVING THE WIRE FROM ITS CONNECTION. Â That being said, on the test plane, the JPI CHT probes were left in place and tie-wrapped to the bundle in the neighborhood of the air leaving the cylinder. Â I was able to measure the temperature drop, of the air (OAT) to the exit air, across cylinder #3 with the #3 probe and across #2 with the #2 probe. Â The #1 CHT probe was placed in the same proximity to the EI probe used to measure the temperature of the air near the alternator. Â The #4 CHT probe was placed in the same proximity to the EI probe used to measure the temperature of the accessory case. Â Both JPI probes showed temps very close to the EI probes used to measure alternator temps and accessory temps,Â respectively.Â Â 

  

 Prior to the FAA climb-cooling tests, I did the same tests with my plane and the JPI 800. The 800 shows percent power so it's trivial to set conditions for 75% power. Â During a Vy climb from 1000 feet to 17,800 feet on an 80 degree day, my CHTs peaked around 470 (roughly 400 on an EI and confirmed during testing with an EI installed  on the test plane) at around 8000 feet. Â Oil temp was stable at 210 before it began to decrease by about the same altitude. Â I ran this same test with the test airplane, climbing to 12,500 feet, and got about the same results, 465 and 205 but it was a cooler day. Â 

  

 

  About 6 months ago, I was flying at tree tops around Lake Berryessa (spelling), a bit northeast of Napa. Â I was near full throttle most of the time. Â OAT was in the high 80s. Â  #3 cylinder began flashing at 465 (that is where I set my limit). Â This surprised me. Â Lots of fat, cool air over a lake and I was still pushing CHTs. Â Anyway, had I not flown for a year with an EI installed in my plane, I would have been worried. Â I know that 465 was somewhere around 400 on an EI. Â 

  

 

  So, if you're using an EI, will you be wondering what the temperature of the aluminum is near the combustion chamber really is when you see 400 degrees? Â If you're using a JPI, will you panic if you see 410 in cruise? Â (my typical cruise temp) Â Maybe.

  

 

  â€œFor those who believe, no proof is necessary. For those who don't believe, no proof is possible.â€Â Â - Stuart Chase

 

  

 

  PS, I wonder why there is so much skepticismÂ over my results with the EI vs JPI.=2 0Â I think someone else needs to go out and duplicate the tests. Â Cliff? Â The next time you get a plane in with a JPI, take one of the spare EIs (you must have a spare) and temporarilyÂ install it and go fly. Â 

  

 

  

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Gary
AuCountry Aviation
Home of Team Grumman

pitts_pilot(at)bellsouth.
Guest

Posted: Thu Mar 26, 2009 1:50 pm Post subject: JPI vs EI

teamgrumman(at)aol.com wrote:

 	  Quote: 	
		   If you turn on a soldering iron and touch the tip with a thermometer 

 (thermal couple) you'll get one reading.  If you move it away from the 

 soldering iron 1/8 of an inch, you'll get another.  The JPI probes 

 touch the cylinder head.  The EI probes sit in the well, heated by the 

 surrounding aluminum.  They are measuring different things.

One measures the temp of the aluminum head, the other measures the temp 
	


of the air in the well ...... and air isn't the best medium for heat 

transfer.

 	  Quote: 	
		   It isn't a question of which one is accurate.  I would bet that both 

 are within 1 degree of being accurate.  Do a little research on 

 thermal couples and you'll find that thermal couples come in all 

 configurations.  Some require grounding, some don't.  Do I want a 

 system that uses a floating ground (EI)?  No.



 I forget a lot from my engineering classes regarding thermal couples, 

 but, as I recall, some thermal couples are used as a source voltage 

 themselves in a circuit and other thermal couples are used is a 

 powered circuit requiring a common source ground.

Go to http://en.wikipedia.org/wiki/Thermocouple for far more info than 
	


you really want   (Google and Wiki are my friends!).    All 

thermocouples generate their own little voltage based on the temperature 

of the junction.   The thermocouple may have a common ground at the 

engine, or a floating input at the instrument.  I consider the common 

ground at the engine poor design.  YMMV.

 	  Quote: 	
		  

 As for which one is better, personally, the JPI makes for a much 

 cleaner installation.  I think the JPI looks more professional and the 

 operating logic is more what I would expect; i.e., less of a learning 

 curve.  The wires are a lot easier to route and you can cut them to 

 length instead of wrapping up and tying up large bundles of wiring. 

  Quite often, on EI installations, the wire gets bundled up under the 

 instrument panel in large wads of wiring.

If the two thermocouple wires go all the way back to the instrument, 
	


both installations shouldn't suffer from trimming off the 'wads'.  Where 

errors occur is when the thermocouple wiring goes through multiple 

connections going back to the instrument.  Each connection introduces 

error ..... unless the connecting contacts are the same type material as 

the wire .... hence 'real' thermocouple connectors.  Depending on the 

instrument, the errors can be removed by adjustments.  However, I think 

for our needs the connector errors are negligible.

snip!!!

Linn

flyv35b(at)minetfiber.com
Guest

Posted: Thu Mar 26, 2009 2:13 pm Post subject: JPI vs EI

[quote] ---

flyv35b(at)minetfiber.com
Guest

Posted: Thu Mar 26, 2009 2:35 pm Post subject: JPI vs EI

  

  2If you turn on a soldering iron and touch the tip with a thermometer  (thermal couple) you'll get one reading.  If you move it away from the  soldering iron 1/8 of an inch, you'll get another.  The JPI probes touch  the cylinder head.  The EI probes sit in the well, heated by the  surrounding aluminum.  They are measuring different things. 2  

  

  Gary, you have obviously done more comparative testing that anyone I know  of and I can't fault what you have done.  Having said that, there still are  a couple of things that have not been explained, to my satisfaction at  least.  Everyone always brings up the different types of CHT probes as an  explanation as to why there is such a larger difference between the JPI and EI  readings.  As I mentioned in an email to the gang recently, EI sells the  exact same type of spring loaded bayonet CHT probe as JPI uses (it is an  option).  And one test I know of with an EI instrument resulted in almost  no temperature variation between the standard P-100 CHT probe and the P-110  spring loaded probe.  That would appear to refute the  2theory 2 that the  temperature difference is due to the different probe styles.  So what else  is there?  Different grounding?

  

  2The wires are a lot easier to route and you can cut them to length instead  of wrapping up and tying up large bundles of wiring.  Quite often, on EI  installations, the wire gets bundled up under the instrument panel in large wads  of wiring.  Looks l ike shit, but, I guess no one but me cares about what  the backside of instrument panel looks like (based on what I see in everything I  work on). 2

  

 I guess you haven't installed an EI system recently.  I agree with you  about the older braided EI wires.  I hated them as well.  EI now uses  the same type of wires as JPI and you can cut them off or get them to not  install the terminals on the circular connector so you can cut them to the exact  length you want the them crimp on the terminals and plug them into the  connector.

  

  2I think someone else needs to go out and duplicate the tests.  Cliff?   The next time you get a plane in with a JPI, take one of the spare EIs  (you must have a spare) and temporarily install it and go fly. 2

  

 I guess you're right, I need to do so further testing as I think there are  still some things that need to be explained.  And I don't think that  the two different style of probes account for 70 F temperature variation, or at  least they shouldn't based on my conversations with EI.  

  

 At one time you were going to test a spring loaded EI probe.  I guess  you never got around to doing that?

  

 Cliff  





 [quote]   ---

GrummanDude

Joined: 15 Jan 2006
Posts: 926
Location: Auburn, CA

Posted: Fri Mar 27, 2009 9:23 am Post subject: JPI vs EI

I got on line last night and did a Google search. Â The grounded thermal couples are a totally different animal than the ungrounded ones. Â If EI is using a spring loaded probe, is it a grounded type or not? Â If it is not, my guess is you won't see any difference in temperatures because of the floating ground. Â In a grounded circuit, it's grounded at the probe. Â Don't ask me to explain how it works. Â  

 

  As for the newer style wires, did EI go to a grounded circuit? Â or do they keep the floating ground?

  

 

  I agree, Cliff. Â There is something else going on. Â Does it matter?

 

 

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Gary
AuCountry Aviation
Home of Team Grumman

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