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EFIS Erratic Temp Readings

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mike(at)vision499.com
Guest

Posted: Mon Feb 01, 2021 6:21 pm Post subject: EFIS Erratic Temp Readings

Hello 

 

I have an EFIS that has erratic temperature readings when the engine is running.

 

Manufacturer has suggested that EMI interference introduced by the ignition system may be the culprit and has suggested shielding the leads with tin plated copper braid that is grounded. I am unable to locate copper braid near me and will have to wait for a delivery from Aircraft Spruce. Will wrapping the leads with aluminum foil replicate the shielding effect for test purposes.

 

The EGT leads (clamp on probe type) are already covered with a braided covering, which I presume is Stainless Steel for physical protection, will this act as an EMI shield and if yes how do I ground it?

 

Copper Braid is sold in 1/8, 1/4, and 3/8 nominal flat width, any guesses as to what size will accommodate k-type thermocouple leads.

 

Thanks

Kellym

Joined: 10 Jan 2006
Posts: 1700
Location: Sun Lakes AZ

Posted: Mon Feb 01, 2021 6:35 pm Post subject: EFIS Erratic Temp Readings

While I suppose it is possible that EMI could cause erratic readings, I 

tend to think the rate of erratic reads would be too fast for you to 

detect. A very high percentage of erratic readings are cause by 

inadequate connectors between the probe and the aircraft harness. Spade 

connectors or ring connectors are common. They can be made to work 

correctly for a period of time, but typically will degrade to inadequate 

conductivity. The only connector I know that has worked 100% of the time 

for me is the Electronics Internation OLC-2 connector(OlC-1 worked too, 

but was harder to use.). It can be obtained in multiples of 5 from EI 

for the bargain price of $1 ea.

https://iflyei.com/product/olc-2/



On 2/1/2021 7:19 PM, mike(at)vision499.com wrote:

 	  Quote: 	
		   Hello

 

 I have an EFIS that has erratic temperature readings when the engine is 

 running.

 

 Manufacturer has suggested that EMI interference introduced by the 

 ignition system may be the culprit and has suggested shielding the leads 

 with tin plated copper braid that is grounded. I am unable to locate 

 copper braid near me and will have to wait for a delivery from Aircraft 

 Spruce. Will wrapping the leads with aluminum foil replicate the 

 shielding effect for test purposes.

 

 The EGT leads (clamp on probe type) are already covered with a braided 

 covering, which I presume is Stainless Steel for physical protection, 

 will this act as an EMI shield and if yes how do I ground it?

 

 Copper Braid is sold in 1/8, 1/4, and 3/8 nominal flat width, any 

 guesses as to what size will accommodate k-type thermocouple leads.

 

 Thanks

_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD

Dave Saylor

Joined: 11 Jan 2015
Posts: 207
Location: GILROY, CA

Posted: Mon Feb 01, 2021 7:11 pm Post subject: EFIS Erratic Temp Readings

I can't tell you how effective foil would be but maybe theÂ group can help troubleshoot.Â  Can you describe how it changes?Â  Quickly, with large displacements, on/off, gradually, etc?Â  Is it around the range you would expect?Â  Is it a single cylinder measurement or similar behavior at different cylinders?



--Dave

On Mon, Feb 1, 2021 at 6:27 PM <mike(at)vision499.com (mike(at)vision499.com)> wrote:



 	  Quote: 	
		  

Hello 

Â 

I have an EFIS that has erratic temperature readings when the engine is running.

Â 

Manufacturer has suggested that EMI interference introduced by the ignition system may be the culprit and has suggested shielding the leads with tin plated copper braid that is grounded. I am unable to locate copper braid near me and will have to wait for a delivery from Aircraft Spruce. Will wrapping the leads with aluminum foil replicate the shielding effect for test purposes.

Â 

The EGT leads (clamp on probe type) are already covered with a braided covering, which I presume is Stainless Steel for physical protection, will this act as an EMI shield and if yes how do I ground it?

Â 

Copper Braid is sold in 1/8, 1/4, and 3/8 nominal flat width, any guesses as to what size will accommodate k-type thermocouple leads.

Â 

Thanks 

Â 

Â 

Â 

Â

_________________
--Dave
KWVI

mikepienaar09(at)gmail.co
Guest

Posted: Mon Feb 01, 2021 9:52 pm Post subject: EFIS Erratic Temp Readings

If I only have sensor connected temperature reading is different for each â€œscanâ€ and varies by up to 150 degrees between max and min.

If I connect more sensors readings become more and more erratic. Even if no sensors are connected â€œghostâ€ readings appear for cylinders not connected with the same reading for EGT and CHT. Ghost readings vary from between -50 to 800 degrees.

 

Hope that helps

 

From: owner-aeroelectric-list-server(at)matronics.com <owner-aeroelectric-list-server(at)matronics.com> On Behalf Of David Saylor

Sent: February 1, 2021 7:10 PM

To: aeroelectric-list <aeroelectric-list(at)matronics.com>

Subject: Re: EFIS Erratic Temp Readings



 

I can't tell you how effective foil would be but maybe the group can help troubleshoot.  Can you describe how it changes?  Quickly, with large displacements, on/off, gradually, etc?  Is it around the range you would expect?  Is it a single cylinder measurement or similar behavior at different cylinders?

 



--Dave

 

On Mon, Feb 1, 2021 at 6:27 PM <mike(at)vision499.com (mike(at)vision499.com)> wrote:

 	  Quote: 	
		  

Hello 

 

I have an EFIS that has erratic temperature readings when the engine is running.

 

Manufacturer has suggested that EMI interference introduced by the ignition system may be the culprit and has suggested shielding the leads with tin plated copper braid that is grounded. I am unable to locate copper braid near me and will have to wait for a delivery from Aircraft Spruce. Will wrapping the leads with aluminum foil replicate the shielding effect for test purposes.

 

The EGT leads (clamp on probe type) are already covered with a braided covering, which I presume is Stainless Steel for physical protection, will this act as an EMI shield and if yes how do I ground it?

 

Copper Braid is sold in 1/8, 1/4, and 3/8 nominal flat width, any guesses as to what size will accommodate k-type thermocouple leads.

 

Thanks

Kellym

Joined: 10 Jan 2006
Posts: 1700
Location: Sun Lakes AZ

Posted: Tue Feb 02, 2021 6:08 am Post subject: EFIS Erratic Temp Readings

Understand that both EGT and CHT are thermocouples that measure small 

changes in resistance. If you have nothing connected the resistance can 

float. If you have less than solid, airtight soldered, crimped or screw 

connection, the resistance will float. I'd still put my money on 

connections that are not airtight. I fought the same issue thinking I 

had bad probes until I switched from spade connectors to the OLC-2 

connectors. Temps are now rock solid. Same for fuel flow sensor. In fact 

on fuel flow the connection improved enough I had to lower the K factor 

between .5-1%. You can get all the connectors needed for $30 for a 6 

cylinder or $20 for a 4 cylinder. AFAIK EI changed all of their 

instruments to the OLC-2 connectors instead of spade connectors.

I seriously doubt you will see much improvement with shielding the whole 

system.



On 2/1/2021 10:51 PM, mikepienaar09(at)gmail.com wrote:

 	  Quote: 	
		   If I only have sensor connected temperature reading is different for 

 each â€œscanâ€ and varies by up to 150 degrees between max and min.

 

 If I connect more sensors readings become more and more erratic. Even if 

 no sensors are connected â€œghostâ€ readings appear for cylinders not 

 connected with the same reading for EGT and CHT. Ghost readings vary 

 from between -50 to 800 degrees.

 

 Hope that helps

 

 *From:*owner-aeroelectric-list-server(at)matronics.com 

 <owner-aeroelectric-list-server(at)matronics.com> *On Behalf Of *David Saylor

 *Sent:* February 1, 2021 7:10 PM

 *To:* aeroelectric-list <aeroelectric-list(at)matronics.com>

 *Subject:* Re: EFIS Erratic Temp Readings

 

 I can't tell you how effective foil would be but maybe theÂ group can 

 help troubleshoot.Â  Can you describe how it changes?Â  Quickly, with 

 large displacements, on/off, gradually, etc?Â  Is it around the range you 

 would expect?Â  Is it a single cylinder measurement or similar behavior 

 at different cylinders?

 

 --Dave

 

 On Mon, Feb 1, 2021 at 6:27 PM <mike(at)vision499.com 

 <mailto:mike(at)vision499.com>> wrote:

 

     Hello

 

     I have an EFIS that has erratic temperature readings when the engine

     is running.

 

     Manufacturer has suggested that EMI interference introduced by the

     ignition system may be the culprit and has suggested shielding the

     leads with tin plated copper braid that is grounded. I am unable to

     locate copper braid near me and will have to wait for a delivery

     from Aircraft Spruce. Will wrapping the leads with aluminum foil

     replicate the shielding effect for test purposes.

 

     The EGT leads (clamp on probe type) are already covered with a

     braided covering, which I presume is Stainless Steel for physical

     protection, will this act as an EMI shield and if yes how do I

     ground it?

 

     Copper Braid is sold in 1/8, 1/4, and 3/8 nominal flat width, any

     guesses as to what size will accommodate k-type thermocouple leads.

 

     Thanks

_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Feb 02, 2021 8:38 am Post subject: EFIS Erratic Temp Readings

At 08:07 AM 2/2/2021, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: Kelly McMullen <kellym(at)aviating.com>



 Understand that both EGT and CHT are thermocouples that measure small changes in resistance. 	


   Actually very TINY changes in VOLTAGE generated

   by the Seebeck effect . . . small temperature

   dependent voltages generated at the junction

   of dissimilar metals.



  	  Quote: 	
		  I had bad probes until I switched from spade connectors to the OLC-2 connectors.

 Temps are now rock solid. 	


   Joint quality in thermocouple feeds

   are important given the very tiny

   voltages involved. 



  	  Quote: 	
		  I seriously doubt you will see much improvement with shielding the whole system. 	


   Agreed, It is exceedingly rare that adding shields

   fixes any problem in an instrumentation

   system.



 

 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Feb 02, 2021 9:41 am Post subject: EFIS Erratic Temp Readings

At 11:51 PM 2/1/2021, you wrote:



  	  Quote: 	
		  If I only have sensor connected temperature reading is different for each scan and varies by up to 150 degrees between max and min. 	


   Whoops . . . missed this out the gate. If the readings

   are THAT erratic you may have something else going on.



   Is this a new condition or did it crop up after a period

   of normal ops?



   Are the readings believable when the engine is not

   running?  Does turning the alternator on/off make

   a difference?



   Are your thermocouples on the engine electrically

   isolated . . . i.e. not grounded to the engine?



   Does the EFIS installation manual speak to the need

   for 'isolated' thermocouples?

  

   The gross excursions of reading sound more like

   a ground loop issue as opposed to connector quality.



 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

mikepienaar09(at)gmail.co
Guest

Posted: Tue Feb 02, 2021 1:51 pm Post subject: EFIS Erratic Temp Readings

From: owner-aeroelectric-list-server(at)matronics.com <owner-aeroelectric-list-server(at)matronics.com> On Behalf Of Robert L. Nuckolls, III

Sent: February 2, 2021 8:48 AM

To: aeroelectric-list(at)matronics.com

Subject: RE: EFIS Erratic Temp Readings

At 11:51 PM 2/1/2021, you wrote:

 	  Quote: 	

If I only have sensor connected temperature reading is different for each scan and varies by up to 150 degrees between max and min. 	

  Whoops . . . missed this out the gate. If the readings

  are THAT erratic you may have something else going on.

  Is this a new condition or did it crop up after a period

  of normal ops?

Aircraft has never flown, only noticed this while testing engine. 

  Are the readings believable when the engine is not

  running?  Does turning the alternator on/off make

  a difference?

Readings seem stable and accurate when engine not running, will test this again.

Will run to-morrow and then disconnect alternator

  Are your thermocouples on the engine electrically

  isolated . . . i.e. not grounded to the engine?

                Not sure what this means

                I have K Type bayonet EGT sensors that clamp onto Exhaust and 1 yellow and 1 red wire that connects directly to MGL RDAC unit

                CHT sensors are under plug with same wire setup

  Does the EFIS installation manual speak to the need

  for 'isolated' thermocouples?

Cannot find a reference for “isolated “ thermocouples

  The gross excursions of reading sound more like

  a ground loop issue as opposed to connector quality.

                I have taken a ground from the EFIS directly to the engine block. The engine mounting bolt is grounded to battery and to the starter motor

                I have also tried it with the RDAC ground attached next to the EGT sensor but this made no difference

None of the leads are joined, they go directly from the sensor to the MGL RDAC unit

Mike

  Bob . . .

  Un impeachable logic: George Carlin asked, "If black boxes

  survive crashes, why don't they make the whole airplane

  out of that stuff?"

Ceengland

Joined: 11 Oct 2020
Posts: 381
Location: MS

Posted: Tue Feb 02, 2021 2:05 pm Post subject: EFIS Erratic Temp Readings

snipped 

           	  Quote: 	
		                  

Cannot find a reference for “isolated “           thermocouples

            snipped         

          

None of the           leads are joined, they go directly from the sensor to the MGL           RDAC unit         

          

Mike

                

     	
     Ask MGL which style (grounded or ungrounded) they require for their     RDAC. 

     

     Ground issues might not be limited to the sensors; poor/inconsistent     ground reference could be related to the RDAC, or the EFIS, or ???.

     

     Charlie

     	          		Virus-free. www.avast.com 		 	 [url=#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2] [/url]

_________________
Charlie

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Feb 02, 2021 7:57 pm Post subject: EFIS Erratic Temp Readings

At 02:12 PM 2/2/2021, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: Dick Tasker <dick(at)thetaskerfamily.com>



 Actually, the voltage is not generated at the junction.  It is effectively generated along the whole length of a conductor due to the temperature difference between the two ends.  In fact, the only reason we get any output to measure is that the two wires of a thermocouple are chosen to have different Seebeck coefficients. 	


   Actually no. There are TWO junctions. One is

   attached to the temperature of interest, the

   second resides at some REFERENCE temperature.

   WAaayyy back when, multiple thermocouples scattered

   about a test airplane at Cessna were paired with

   'reference' thermocouples immersed in an distilled

   water ice bath (0 degrees C). 



   The real temperature of interest is deduced by

   comparing the test thermocouple with the reference

   thermocouple. Views -A- and -B- in this excerpt

   from the 'Connection.



  http://www.aeroelectric.com/articles/Thermocouple%20Junctions.pdf



   The reference junction doesn't have to be an ice bath,

   it can be part of the indicating instrument wherein

   'reference' is cabin environment temperature . . . there

   will be compensating thermistors in the instrument to

   improve accuracy over a range of cabin environments.



   Non-electronic thermocouple instruments of old actually

   measured that difference voltage with meter movements that read

   full scale with tens of millivolts applied. In these

   cases, there was considerable current flowing in the

   thermocouple leads compared to electronic displays.

   Hence, thermocouple wire lengths and wire gages were

   critical to accurate measurement.



   Electronic displays don't need to draw current from

   the thermocouples hence, wire length and gage

   don't matter . . . there are no voltage drops in the

   lead wires. JOINTS in those runs are critical

   in that they need to occur in pairs so that potentially

   parasitic junctions cancel each other out. See chapter

   10 in the 'Connection.



     



 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Feb 03, 2021 8:39 am Post subject: EFIS Erratic Temp Readings

 	  Quote: 	
		    Is this a new condition or did it crop up after a period

   of normal ops?        



 Aircraft has never flown, only noticed this while testing engine. 	


    Good data point.



  	  Quote: 	
		    Are the readings believable when the engine is not

   running?  Does turning the alternator on/off make

   a difference?



 Readings seem stable and accurate when engine not running, will test this again.



 Will run to-morrow and then disconnect alternator 	


    Also, while exploring effects of alternator

    operation, you might dis-mount temperature

    sensors from engine and let them hang free

    not touching engine.



 

  	  Quote: 	
		    Are your thermocouples on the engine electrically

   isolated . . . i.e. not grounded to the engine?



                 Not sure what this means



                 I have K Type bayonet EGT sensors that clamp onto Exhaust and 1 yellow and 1 red wire that connects directly to MGL RDAC unit



                 CHT sensors are under plug with same wire setup 	


    The reason for this question is founded in

    characteristics of legacy thermocouples designed

    to drive stand-alone instruments. Given that

    there were no wires at the instrument ends

    attached to ground or other ship's wiring, the

    engine thermocouples could be quite simply

    constructed with the junctions literally

    'grounded' to the sensor shell.



    Such sensors might not play well in the modern

    EFIS sandbox.



    I rather suspect that everyone builds isolated

    (insulated) thermocouples such that no

    electrical continuity exists between the thermocouple

    conductors and the sensor enclosure. These would

    be functionally friendly in any engine management

    system.



  	  Quote: 	
		    The gross excursions of reading sound more like

   a ground loop issue as opposed to connector quality.



                 I have taken a ground from the EFIS directly to the engine block. The engine mounting bolt is grounded to battery and to the starter motor



                 I have also tried it with the RDAC ground attached next to the EGT sensor but this made no difference 	


    When you installed this experimental ground,

    were there any OTHER grounds in operation? I.e.

    DC power ground?  To absolutely eliminate the

    possibility of this being a ground loop problem.

    ALL grounds would need to go ONLY to crankcase.

    However, if your thermocouples are of the

    insulated variety, ground loop(s) are almost

    assuredly not the problem.



    Have you conversed with the manufacturer about

    this?

  	  Quote: 	
		   



 None of the leads are joined, they go directly from the sensor to the MGL RDAC unit

 	


    Okay.



 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Feb 03, 2021 11:19 am Post subject: EFIS Erratic Temp Readings

 	  Quote: 	
		    It is generated along the whole length of the wire based on the temperature gradient along the wire in question.  The only reason we get anything to measure is that the two wires used in the thermocouple have different coefficients.



 Not that all this is terribly pertinent in actual applications, but one should know how electrical phenomena actually work. 	


   That's the assertion I was having trouble with.

   There are thermocouple installations in petroleum

   refineries that are hundreds of feet long and

   traverse a huge range of temperatures . . . if

   'gradient along the length' is in play, how

   can such installations offer meaningful readings

   from 'the far end'?



   I would draw your attention to View -B- of the

   illustration I posted. It's entirely valid to

   EXTEND a thermocouple any necessary distance

   with two copper wires . . . as long as you KNOW

   the temperature of the environment where the

   transition from t/c wire to copper takes place.

   That joint becomes the reference junction.



   I've not encountered a situation where length

   or surrounding environment of extension conductors

   have an effect on calibration of a 'zero current'

   thermocouple installation.



 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Feb 03, 2021 4:28 pm Post subject: EFIS Erratic Temp Readings

 	  Quote: 	
		  Think about it.  The thermocouple that is hundreds of feet long that goes through lots of temperature transitions from one end to the other generates voltage all along its length - sometimes positive and sometimes negative, depending on the temperature gradient along that particular section.  The only thing that matters is the total temperature difference between the two ends.  All other intermediate transitions cancel out.  It's like putting lots of batteries in series - some pointing one way and others pointing the other.  The net result is just the sum of all the batteries - positive and negative adding and subtracting respectively. 	


   Suppose I brought 10' of chromel wire together at a

   sense junction with 100' of alumel wire. Assume further

   that the far ends of both wires terminate at a

   temperature compensated thermocouple meter.

   

   Suppose further than the 100' strand was coiled up and

   immersed in 100C water while the 10' strand remained

   at room temperature.



   Is it your understanding that serious errors in

   temperature reading would be generated by gross

   differences in temperature dependent voltage

   sources within those two wires?  I.e. thermocouple

   class voltages (microvolts) are generated by

   warming two identical molecules of a conductor?



   What is this phenomenon called? Can you point

   me to literature that explains it?  



 

 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Wed Feb 03, 2021 5:17 pm Post subject: Re: EFIS Erratic Temp Readings

One time at work I measured millivolts at the end of a two wire fire alarm cable that was buried underground.

 Water had gotten into the cable and turned it into a battery.

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Feb 05, 2021 6:21 am Post subject: EFIS Erratic Temp Readings

 	  Quote: 	
		    	  Quote: 	
		    What is this phenomenon called? Can you point

   me to literature that explains it? 	


 It is called the Seebeck effect.  I previously included a link that explains the effect: tinyurl.com/3njog7qv Also refer to the links in that article for more information.



 For practical purposes you can certainly continue to say that the voltage is generated at each junction and that nothing happens in between.  All I am doing is explaining what actually happens.

 	


   I had to dig out references I've not consulted

   for oh . . . say . . . 40 years? Even my

   revered CRC Handbook of Chemistry and Physics

   doesn't dig this deep into the phenomenon. But

   I did find some recitations on the phenomenon

   Dick brought to the conversation.



   Thermocouples are but one instance where the

   characteristics of materials push electrons

   around. These are studies in electro-motive

   physics.



   There are many instances where 'differences'

   in two materials encourage motion of electrons

   under certain conditions.



   MECHANICALLY induced electro-motion:



   Shuffle your rubber soled shoes on a carpet

   in dry weather and you build a potential on

   your body that can produce visible sparks

   when discharged to some metal object or perhaps

   another person. Leather soled shoes, yeah but

   not so much.



   Mechanically modulated magnetic fields in

   alternators and generators produce very

   significant electron motion that keeps our

   instrument panels lit up.



   CHEMICALLY induced electro-motion:



   Conductive plates pasted with two different compounds

   of lead submerged in mixture of sulfuric acid will

   offers a potential for flow of electrons . . .

   what's more it's reversible. But if the plates

   are identical, no joy.



   Pieces of zinc and copper pushed into a lemon

   produces a measurable voltage between the

   two metals; but use two copper pieces and

   the effect goes away.



   THERMALLY induced electro-motion:



   put any two dissimilar metals in intimate

   contact with each other and they will produce

   a voltage based on temperature.



   I had not picked up on the phenomenon Dick

   cited because it's a layer down from

   the practical physics that applies to our

   craft.



   About 1821 this observant guy Seebeck discovered

   the thermo-electric effects in a loop of two

   metals wherein their joinings (junctions) were

   at different temperatures. The energy flow generated

   in that loop of wire was directly related to

   the magnitude of temperature difference between

   the two junctions. If the alloys were carefully

   controlled and tiny voltages accurately measured

   that energy would represent real temperatures.

   Hence the foundation of the thermocouple driven

   instruments spanning over a century of aviation

   practice.



   ELECTRICALLY induced thermo-motion:



   A few years later in 1834, another sharp fellow

   Peltier observed that the thermo-electric generation

   was reversible. I.e. if you replaced the thermocouple

   measuring instrument with a current source, those

   same two junctions would assume temperatures above

   and below ambient. Effects difficult to observe

   due to the very tiny effects. But they were real

   and could be detected.



   It wasn't until years later in 1854 that another

   sharp fellow Thomson identified thermo-electric

   effects within conductors that explained how

   Seebeck and Peltier's discoveries worked.

   The longitudinal thermo-electric property

   within conductors was named after Thomson. The

   Seebeck, Peltier and Thomson effects combine

   to complete a story of how thermocouples

   function to monitor engines and thermoelectric

   coolers refrigerate beer.



   At the ripe age of 22, Thompson was awarded

   a professorship in natural philosophy (physics).

   Thompson was only 30 years old when he

   identified and quantified this longitudinal

   behavior of thermodynamics in a single

   conductor. Thompson was better known by his

   British title of station: Lord Kelvin.



   Dick cited the next level down in the

   physics of Seebeck and Peltier effects;

   accurate but not generally included

   in practical explanations for the two

   technologies. It's kinda like dissecting

   the physics of lubricity and viscosity

   when considering suitability to task

   for lubricating oils in engines.



   His only error was to identify it as the

   'Seebeck effect' as opposed to the 

   'Thomson effect'.



   It was an interesting excursion to

   a time when I probably should have

   been paying more attention in class!

   Thanks for the trip Dick!



 Bob . . . 



 

 -----------------------------

 Bob Nuckolls

 AeroElectric Connection

 P.O. Box 130

 Medicine Lodge, KS  67104-0130

 Mobile: 316-209-7528

 Web:  http://aeroelectric.com

 ------------------------------ 



 



  	  Quote: 	
		  Dick



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   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Feb 06, 2021 9:37 am Post subject: EFIS Erratic Temp Readings

At 11:51 PM 2/1/2021, you wrote:



  	  Quote: 	
		  If I only have sensor connected temperature reading is different for each â€œscanâ€ and varies by up to 150 degrees between max and min.



 If I connect more sensors readings become more and more erratic. Even if no sensors are connected â€œghostâ€ readings appear for cylinders not connected with the same reading for EGT and CHT. Ghost readings vary from between -50 to 800 degrees.



  



 Hope that helps 	


   Mike, I was reviewing this thread and another

   thought occurs. While testing with 'no sensors'

   what was the condition of the open inputs?

   

   Did you put shorts across them or were they

   simply disconnected?



 

 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

mikepienaar09(at)gmail.co
Guest

Posted: Sat Feb 06, 2021 12:54 pm Post subject: EFIS Erratic Temp Readings

From: owner-aeroelectric-list-server(at)matronics.com <owner-aeroelectric-list-server(at)matronics.com> On Behalf Of Robert L. Nuckolls, III

Sent: February 6, 2021 9:36 AM

To: aeroelectric-list(at)matronics.com

Subject: RE: EFIS Erratic Temp Readings

 

At 11:51 PM 2/1/2021, you wrote:





  Mike, I was reviewing this thread and another

  thought occurs. While testing with 'no sensors'

  what was the condition of the open inputs?

  

  Did you put shorts across them or were they

  simply disconnected?

 

                No, they were not shorted, simply disconnected. Will try with them shorted next week.

                I would never have thought of shorting them

 

                I did remove the alternator and ran the engine with no alternator and that made no difference,

                Readings were still erratic

 

Thanks

 

Mike



  Bob . . .



  Un impeachable logic: George Carlin asked, "If black boxes

  survive crashes, why don't they make the whole airplane

  out of that stuff?"

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Feb 06, 2021 2:34 pm Post subject: EFIS Erratic Temp Readings

 	  Quote: 	
		                   No, they were not shorted, simply disconnected. Will try with them shorted next week.



                 I would never have thought of shorting them 	




    It used to be pretty much standard that

    the input to a thermocouple driven display

    device was pretty low impedance. Modern

    electronics allows us to resolve those

    tiny voltages with displays having very

    high input impedances.



    I have data acquisition equipment that

    requires unused channels to be 'tied down',

    i.e. shorted out. Otherwise they 'wander'

    in response to stimuli in the environment.

  

    Your EFIS may be similarly designed.

  	  Quote: 	
		   



                 I did remove the alternator and ran the engine with no alternator and that made no difference,



                 Readings were still erratic 	


    Hmmmm . . . so probably no value in exploring

    noise on the DC power line.



    See what the thing does with all inputs 'locked

    down' . . . then if stable . . . try adding one

    t/c at a time.



 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

Ceengland

Joined: 11 Oct 2020
Posts: 381
Location: MS

Posted: Sat Feb 06, 2021 4:38 pm Post subject: EFIS Erratic Temp Readings

snipped

      	  Quote: 	
		                  

  

             Did you put shorts across them or were they

             simply disconnected? 

                    

                No, they were not shorted,           simply disconnected. Will try with them shorted next week.         

                I would never have thought           of shorting them 

                    

                I did remove the alternator           and ran the engine with no alternator and that made no           difference,         

                Readings were still erratic             

                    

Thanks 

                    

Mike

                

     	
     Hi Mike, 

     

     Can you remind us whether the engine is 'standard' mags & carb     (or Bendix style injection), or if it has some combination of     electronic ignition/fuel injection?

     

     Thanks,

     Charlie

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_________________
Charlie

mikepienaar09(at)gmail.co
Guest

Posted: Mon Feb 08, 2021 11:29 am Post subject: EFIS Erratic Temp Readings

Hi Mike, 



Can you remind us whether the engine is 'standard' mags & carb (or Bendix style injection), or if it has some combination of electronic ignition/fuel injection?

 

It is a LOM engine with magneto’s only and mechanical fuel injection. No electronics on the engine at all

 

Mike

Thanks,

Charlie

 



Virus-free. www.avast.com

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