Topics

Firewall electric thru connections

Bruce Crain
 

It seems like Justin Mace had a connection for multiple wiring bundle with a screw off quick disconnect that went thru the firewall. It was fireproof and soldered on the inside with barbs like molex connectors on a sub-d. It seemed old school perhaps WWII. Does anyone have any intel of where and what to buy? Would be nice to have screw connections for wiring firewall forward for solid connections. Anyone, anyone, Buehler?
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Jay Scheevel
 

Hi Bruce,
I have several metal bayonet type connectors on my firewall. everything disconnects at the firewall on my rig. One is a 24 conductor 1.25" diamerer, that handles all the various engine monitoring except thermocouples. The size is overkill but was given to me by a friend, so was free and is very robust. I think it came out of a Huey helicopter. the others I ordered from Newark. they come with choice of number of conductors from 2 to 8. Also metal twist off bayonet type. Let me know if you want me to look up the part numbers and I will send tomorrow.

Cheers,
Jay

Sent from my Verizon Wireless 4G LTE DROID


Bruce Crain <jcrain2@...> wrote:

It seems like Justin Mace had a connection for multiple wiring bundle with a screw off quick disconnect that went thru the firewall.  It was fireproof and soldered on the inside with barbs like molex connectors on a sub-d.  It seemed old school perhaps WWII.  Does anyone have any intel of where and what to buy?  Would be nice to have screw connections for wiring firewall forward for solid connections.  Anyone, anyone, Buehler?
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4 Cops Fired Over Death of Unarmed Black Man
http://thirdpartyoffers.juno.com/TGL3131/5ecdd9513f325950789bst04vuc2
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Corbin
 

Hey Bruce,

I have the ones attached; referred to as MIL connectors (MIL-DTL-5015).  Is this what you are looking for?  McMaster has them.



Corbin

On May 26, 2020, at 10:07 PM, Bruce Crain <jcrain2@...> wrote:

It seems like Justin Mace had a connection for multiple wiring bundle with a screw off quick disconnect that went thru the firewall.  It was fireproof and soldered on the inside with barbs like molex connectors on a sub-d.  It seemed old school perhaps WWII.  Does anyone have any intel of where and what to buy?  Would be nice to have screw connections for wiring firewall forward for solid connections.  Anyone, anyone, Buehler?
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Sponsored by https://www.newser.com/?utm_source=part&utm_medium=uol&utm_campaign=rss_taglines_more

Twitter Slaps Warning on Trump's Tweets
http://thirdpartyoffers.juno.com/TGL3131/5ecdd950dd2045950789bst04vuc1
4 Cops Fired Over Death of Unarmed Black Man
http://thirdpartyoffers.juno.com/TGL3131/5ecdd9513f325950789bst04vuc2
Gov. Whitmer's New Headache Involves Her Husband, a Boat
http://thirdpartyoffers.juno.com/TGL3131/5ecdd9511f77a5950789bst04vuc3




--

Corbin 
N33QR

Bruce Crain
 

Corbin and Jay this might be just the right stuff!  Do you think the barbs will connect a strong enough signal for egt/cht ie tight enough for good transmission for those gauges?  Also, what diameter are the thru connects?
Thank you!
Bruce Crain
!
Please note: message attached

From: "Corbin via groups.io" <c_geiser@...>
To: main@q-list.groups.io
Subject: Re: [Q-List] Firewall electric thru connections
Date: Wed, 27 May 2020 05:02:21 -0500



Corbin
 

Yes, in fact all of my electrical and engine probes pass through these type connectors.  I have three on my firewall and have appreciated them each time I have needed to remove the engine; making it much quicker to disconnect.

Corbin

On May 27, 2020 at 7:47 AM, Bruce Crain <jcrain2@...> wrote:

Corbin and Jay this might be just the right stuff!  Do you think the barbs will connect a strong enough signal for egt/cht ie tight enough for good transmission for those gauges?  Also, what diameter are the thru connects?
Thank you!
Bruce Crain
!
Please note: message attached

From: "Corbin via groups.io" <c_geiser@...>
To: main@q-list.groups.io
Subject: Re: [Q-List] Firewall electric thru connections
Date: Wed, 27 May 2020 05:02:21 -0500






--

Corbin 
N33QR

Sam Hoskins
 

Bruce, I use automotive Weather Pack connector in several places. For my EGT/CHT wires I use B&C knife connector, covered with heat shrink.

Sam 


On Tue, May 26, 2020, 10:07 PM Bruce Crain <jcrain2@...> wrote:
It seems like Justin Mace had a connection for multiple wiring bundle with a screw off quick disconnect that went thru the firewall.  It was fireproof and soldered on the inside with barbs like molex connectors on a sub-d.  It seemed old school perhaps WWII.  Does anyone have any intel of where and what to buy?  Would be nice to have screw connections for wiring firewall forward for solid connections.  Anyone, anyone, Buehler?
____________________________________________________________
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Jay Scheevel
 

Hi Bruce,

 

Just a note concerning the EGT and CHT thermocouples passing through the firewall. I originally planned to run the EGT and CHT connections through the large connector that Corbin showed (same as mine). I nixed this idea after reading Bob Nuckols articles. He noted that it is possible to break the thermocouple wire and insert a connector of different metal, but if one side of the junction is hotter or cooler than the other side of the junction (like going through the firewall), this temperature difference across the junction will distort the temperature that the instrument reads. I avoided this issue by using male and female plugs at the firewall that are constructed of the same metals as the thermocouple, so essentially there is no junction. Let me know if you want to use some of these connectors and I will send you the details. They are not fireproof, but they are laboratory quality, so I felt comfortable using them.

 

Cheers,

Jay

 

From: main@Q-List.groups.io <main@Q-List.groups.io> On Behalf Of Bruce Crain
Sent: Wednesday, May 27, 2020 6:45 AM
To: main@Q-List.groups.io
Subject: Re: [Q-List] Firewall electric thru connections

 

Corbin and Jay this might be just the right stuff!  Do you think the barbs will connect a strong enough signal for egt/cht ie tight enough for good transmission for those gauges?  Also, what diameter are the thru connects?

Thank you!

Bruce Crain
!
Please note: message attached

From: "Corbin via groups.io" <c_geiser@...>
To: main@q-list.groups.io
Subject: Re: [Q-List] Firewall electric thru connections
Date: Wed, 27 May 2020 05:02:21 -0500

 

Jim Patillo
 

Bruce, I use one 24 pin Molex twist connector for everything including CHT/EGT.
Connector is bulkhead mounted on firewall in front of pax rudder pedals.

Jim
N46JP Q200

Sent from Outer Space


From: main@Q-List.groups.io <main@Q-List.groups.io> on behalf of Bruce Crain <jcrain2@...>
Sent: Wednesday, May 27, 2020 5:45:08 AM
To: main@Q-List.groups.io <main@Q-List.groups.io>
Subject: Re: [Q-List] Firewall electric thru connections
 
Corbin and Jay this might be just the right stuff!  Do you think the barbs will connect a strong enough signal for egt/cht ie tight enough for good transmission for those gauges?  Also, what diameter are the thru connects?
Thank you!
Bruce Crain
!
Please note: message attached

From: "Corbin via groups.io" <c_geiser@...>
To: main@q-list.groups.io
Subject: Re: [Q-List] Firewall electric thru connections
Date: Wed, 27 May 2020 05:02:21 -0500



kingdws@...
 

Bruce do a search for bulkhead connector sub-d 

That will get you multiple sources. The soldered ends aren't as common in aerospace use as soldering is seen as less reliable but can still be found as std or a milspec item

Dave

On Tue, May 26, 2020, 20:07 Bruce Crain <jcrain2@...> wrote:
It seems like Justin Mace had a connection for multiple wiring bundle with a screw off quick disconnect that went thru the firewall.  It was fireproof and soldered on the inside with barbs like molex connectors on a sub-d.  It seemed old school perhaps WWII.  Does anyone have any intel of where and what to buy?  Would be nice to have screw connections for wiring firewall forward for solid connections.  Anyone, anyone, Buehler?
____________________________________________________________
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http://thirdpartyoffers.juno.com/TGL3131/5ecdd9513f325950789bst04vuc2
Gov. Whitmer's New Headache Involves Her Husband, a Boat
http://thirdpartyoffers.juno.com/TGL3131/5ecdd9511f77a5950789bst04vuc3



Richard Thomson
 

Jay, that was just the point I was going to make. Any connections between thermocouple and instrument need to be same material or you will get a "Cold Junction".  That can change the actual temperature shown by a fair margin.

Also its is all very well going for the heavy option of connectors on your firewall, make sure you do your safety analysis, i.e. if it happens to become disconnected what effect will it have on your flight.  Does it have ratchet locking or do you need to wire lock.

Being an old Aircraft Electrician, I have gone for the lighter, cheaper option of wired direct, but then my MGL RDAC is firewall fwd anyway, so that reduces the cables through the wall.

Rich T.


On 27/05/2020 17:16, Jay Scheevel wrote:

Hi Bruce,

 

Just a note concerning the EGT and CHT thermocouples passing through the firewall. I originally planned to run the EGT and CHT connections through the large connector that Corbin showed (same as mine). I nixed this idea after reading Bob Nuckols articles. He noted that it is possible to break the thermocouple wire and insert a connector of different metal, but if one side of the junction is hotter or cooler than the other side of the junction (like going through the firewall), this temperature difference across the junction will distort the temperature that the instrument reads. I avoided this issue by using male and female plugs at the firewall that are constructed of the same metals as the thermocouple, so essentially there is no junction. Let me know if you want to use some of these connectors and I will send you the details. They are not fireproof, but they are laboratory quality, so I felt comfortable using them.

 

Cheers,

Jay

 

From: main@Q-List.groups.io <main@Q-List.groups.io> On Behalf Of Bruce Crain
Sent: Wednesday, May 27, 2020 6:45 AM
To: main@Q-List.groups.io
Subject: Re: [Q-List] Firewall electric thru connections

 

Corbin and Jay this might be just the right stuff!  Do you think the barbs will connect a strong enough signal for egt/cht ie tight enough for good transmission for those gauges?  Also, what diameter are the thru connects?

Thank you!

Bruce Crain
!
Please note: message attached

From: "Corbin via groups.io" <c_geiser@...>
To: main@q-list.groups.io
Subject: Re: [Q-List] Firewall electric thru connections
Date: Wed, 27 May 2020 05:02:21 -0500

 

Joe Hood
 

I used to enjoy wiring up Canon plugs on A-4s. Had no idea on the dissimilar metals and "cold junctions." Can't the instrument be re-calibrated?

 

Found a pretty good primer on thermocouple extensions here (I learn something new every day):

https://www.omega.com/en-us/resources/thermocouple-wire

Rick Hole
 

For those who are using connectors not if thermocouple material: a difference in temperature on the two sides of the connection will induce an error.  It will be equal on each sensor so for EGT the error is harmless.
The thermocouple effect on this connector is much smaller than for a junction of the two thermocouple metals.  My tests at heating each side if the connection separately with hot air (hotter than engine compartment) showed a couple degrees of error, not enough to worry about.
With CHT we are concerned about red line and a couple degrees might be significant.  The error will be equal for all CHT channels so comparing cylinder temps will remain valid.
Rick Hole

On Thu, May 28, 2020, 6:20 AM Joe Hood <joe.hood@...> wrote:

I used to enjoy wiring up Canon plugs on A-4s. Had no idea on the dissimilar metals and "cold junctions." Can't the instrument be re-calibrated?

 

Found a pretty good primer on thermocouple extensions here (I learn something new every day):

https://www.omega.com/en-us/resources/thermocouple-wire

Jay Scheevel
 

Corrections for connectors of differing metals are difficult to do unless you know the temperatures on both sides of the junction in real time. This is practically impossible, since you would have instrument both sides of the connector with more thermocouples. Any two dissimilar metal junctions respond to temperature with a unique function. If you have, say a copper connector under the firewall, one end of the copper adds a temperature dependent voltage and the other end reduces the voltage same amount, but only if both ends are at the same temperature. So that is the reason for the problem crossing the firewall. The connection calibration at the instrument or engine monitoring box is built in to the software so is predictable and transparent to the user.

 

I am attaching some info on how I did my firewall connectors for EGT and CHT. I have 6 cylinders, so I built up two plugs, each carrying 3 EGT’s and 3 CHT’s, one set on the left and one on the right (see last photo below). The first pic below is on the front of the firewall, right side. This is before I connected the wires into the individual plugs, but you can see the 6 holes for them in the aluminum “container” that I built to contain all 6 individual male plugs. When you disconnect the plug from the firewall, there are 12 prongs! The second pic is on the back side of the firewall. There is no aluminum “container” on this side since they are held down by the two phenolic blocks on either side of the hole. The 6 separate two-prong plugs have a convenient hole in the housing that allowed me to put piece of welding rod through them 3 at a time and gang them together. The ends of the welding rod are clamped to firewall by the phenolic blocks. The black screw heads on the firewall side (first photo) go through the firewall into threaded holes in the phenolic on the back side to secure the plug in place and seal the hole. I am loading the spec sheet for the connectors and some Nuckolls article on thermocouples into the files section, if you want more info.

 

Cheers,

Jay Scheevel, Tri-Q2 N8WQ, 92 hours

From: main@Q-List.groups.io <main@Q-List.groups.io> On Behalf Of Joe Hood
Sent: Thursday, May 28, 2020 6:20 AM
To: main@Q-List.groups.io
Subject: Re: [Q-List] Firewall electric thru connections

 

I used to enjoy wiring up Canon plugs on A-4s. Had no idea on the dissimilar metals and "cold junctions." Can't the instrument be re-calibrated?

 

Found a pretty good primer on thermocouple extensions here (I learn something new every day):

https://www.omega.com/en-us/resources/thermocouple-wire

Bruce Crain
 

If the instrument is “amplified signal” such as KN egt/cht gauge will it make a difference?  The material coming out of the KN instrument is the same wire as the probe wires.
Bruce


On May 28, 2020, at 9:39 AM, Jay Scheevel <jay@...> wrote:



Corrections for connectors of differing metals are difficult to do unless you know the temperatures on both sides of the junction in real time. This is practically impossible, since you would have instrument both sides of the connector with more thermocouples. Any two dissimilar metal junctions respond to temperature with a unique function. If you have, say a copper connector under the firewall, one end of the copper adds a temperature dependent voltage and the other end reduces the voltage same amount, but only if both ends are at the same temperature. So that is the reason for the problem crossing the firewall. The connection calibration at the instrument or engine monitoring box is built in to the software so is predictable and transparent to the user.

 

I am attaching some info on how I did my firewall connectors for EGT and CHT. I have 6 cylinders, so I built up two plugs, each carrying 3 EGT’s and 3 CHT’s, one set on the left and one on the right (see last photo below). The first pic below is on the front of the firewall, right side. This is before I connected the wires into the individual plugs, but you can see the 6 holes for them in the aluminum “container” that I built to contain all 6 individual male plugs. When you disconnect the plug from the firewall, there are 12 prongs! The second pic is on the back side of the firewall. There is no aluminum “container” on this side since they are held down by the two phenolic blocks on either side of the hole. The 6 separate two-prong plugs have a convenient hole in the housing that allowed me to put piece of welding rod through them 3 at a time and gang them together. The ends of the welding rod are clamped to firewall by the phenolic blocks. The black screw heads on the firewall side (first photo) go through the firewall into threaded holes in the phenolic on the back side to secure the plug in place and seal the hole. I am loading the spec sheet for the connectors and some Nuckolls article on thermocouples into the files section, if you want more info.

 

Cheers,

Jay Scheevel, Tri-Q2 N8WQ, 92 hours

<image002.jpg>
<image006.jpg>

<image008.jpg>

From: main@Q-List.groups.io <main@Q-List.groups.io> On Behalf Of Joe Hood
Sent: Thursday, May 28, 2020 6:20 AM
To: main@Q-List.groups.io
Subject: Re: [Q-List] Firewall electric thru connections

 

I used to enjoy wiring up Canon plugs on A-4s. Had no idea on the dissimilar metals and "cold junctions." Can't the instrument be re-calibrated?

 

Found a pretty good primer on thermocouple extensions here (I learn something new every day):

https://www.omega.com/en-us/resources/thermocouple-wire



Jay Scheevel
 

Can you send a picture of your gauge? Is it free standing with only inputs being the two thermocouple wires?

Sent from my Verizon Wireless 4G LTE DROID


Bruce Crain <jcrain2@...> wrote:

If the instrument is “amplified signal” such as KN egt/cht gauge will it make a difference?  The material coming out of the KN instrument is the same wire as the probe wires.
Bruce


On May 28, 2020, at 9:39 AM, Jay Scheevel <jay@...> wrote:



Corrections for connectors of differing metals are difficult to do unless you know the temperatures on both sides of the junction in real time. This is practically impossible, since you would have instrument both sides of the connector with more thermocouples. Any two dissimilar metal junctions respond to temperature with a unique function. If you have, say a copper connector under the firewall, one end of the copper adds a temperature dependent voltage and the other end reduces the voltage same amount, but only if both ends are at the same temperature. So that is the reason for the problem crossing the firewall. The connection calibration at the instrument or engine monitoring box is built in to the software so is predictable and transparent to the user.

 

I am attaching some info on how I did my firewall connectors for EGT and CHT. I have 6 cylinders, so I built up two plugs, each carrying 3 EGT’s and 3 CHT’s, one set on the left and one on the right (see last photo below). The first pic below is on the front of the firewall, right side. This is before I connected the wires into the individual plugs, but you can see the 6 holes for them in the aluminum “container” that I built to contain all 6 individual male plugs. When you disconnect the plug from the firewall, there are 12 prongs! The second pic is on the back side of the firewall. There is no aluminum “container” on this side since they are held down by the two phenolic blocks on either side of the hole. The 6 separate two-prong plugs have a convenient hole in the housing that allowed me to put piece of welding rod through them 3 at a time and gang them together. The ends of the welding rod are clamped to firewall by the phenolic blocks. The black screw heads on the firewall side (first photo) go through the firewall into threaded holes in the phenolic on the back side to secure the plug in place and seal the hole. I am loading the spec sheet for the connectors and some Nuckolls article on thermocouples into the files section, if you want more info.

 

Cheers,

Jay Scheevel, Tri-Q2 N8WQ, 92 hours

<image002.jpg>
<image006.jpg>

<image008.jpg>

From: main@Q-List.groups.io <main@Q-List.groups.io> On Behalf Of Joe Hood
Sent: Thursday, May 28, 2020 6:20 AM
To: main@Q-List.groups.io
Subject: Re: [Q-List] Firewall electric thru connections

 

I used to enjoy wiring up Canon plugs on A-4s. Had no idea on the dissimilar metals and "cold junctions." Can't the instrument be re-calibrated?

 

Found a pretty good primer on thermocouple extensions here (I learn something new every day):

https://www.omega.com/en-us/resources/thermocouple-wire

Bruce Crain
 

I suppose it is free standing?  It is fairly old but has a toggle switching between egt/cht and each probe has two designated wires going all the way from the head to the probe.
Bruce


---------- Original Message ----------
From: "Jay Scheevel" <jay@...>
To: main@Q-List.groups.io
Subject: Re: [Q-List] Firewall electric thru connections
Date: Thu, 28 May 2020 16:49:34 -0600

Can you send a picture of your gauge? Is it free standing with only inputs being the two thermocouple wires?
 
Sent from my Verizon Wireless 4G LTE DROID



Bruce Crain <jcrain2@...> wrote:

If the instrument is “amplified signal” such as KN egt/cht gauge will it make a difference?  The material coming out of the KN instrument is the same wire as the probe wires.

Bruce

 

On May 28, 2020, at 9:39 AM, Jay Scheevel <jay@...> wrote:

Corrections for connectors of differing metals are difficult to do unless you know the temperatures on both sides of the junction in real time. This is practically impossible, since you would have instrument both sides of the connector with more thermocouples. Any two dissimilar metal junctions respond to temperature with a unique function. If you have, say a copper connector under the firewall, one end of the copper adds a temperature dependent voltage and the other end reduces the voltage same amount, but only if both ends are at the same temperature. So that is the reason for the problem crossing the firewall. The connection calibration at the instrument or engine monitoring box is built in to the software so is predictable and transparent to the user.

 

I am attaching some info on how I did my firewall connectors for EGT and CHT. I have 6 cylinders, so I built up two plugs, each carrying 3 EGT’s and 3 CHT’s, one set on the left and one on the right (see last photo below). The first pic below is on the front of the firewall, right side. This is before I connected the wires into the individual plugs, but you can see the 6 holes for them in the aluminum “container” that I built to contain all 6 individual male plugs. When you disconnect the plug from the firewall, there are 12 prongs! The second pic is on the back side of the firewall. There is no aluminum “container” on this side since they are held down by the two phenolic blocks on either side of the hole. The 6 separate two-prong plugs have a convenient hole in the housing that allowed me to put piece of welding rod through them 3 at a time and gang them together. The ends of the welding rod are clamped to firewall by the phenolic blocks. The black screw heads on the firewall side (first photo) go through the firewall into threaded holes in the phenolic on the back side to secure the plug in place and seal the hole. I am loading the spec sheet for the connectors and some Nuckolls article on thermocouples into the files section, if you want more info.

 

Cheers,

Jay Scheevel, Tri-Q2 N8WQ, 92 hours

<image002.jpg>
<image006.jpg>
<image008.jpg>

From: main@Q-List.groups.io <main@Q-List.groups.io> On Behalf Of Joe Hood
Sent: Thursday, May 28, 2020 6:20 AM
To: main@Q-List.groups.io
Subject: Re: [Q-List] Firewall electric thru connections

 

I used to enjoy wiring up Canon plugs on A-4s. Had no idea on the dissimilar metals and "cold junctions." Can't the instrument be re-calibrated?

 

Found a pretty good primer on thermocouple extensions here (I learn something new every day):

https://www.omega.com/en-us/resources/thermocouple-wire

 


Jay Scheevel
 

Then that instrument is essentially a voltage meter (with a selector switch), that is calibrated to directly read in Degrees/Temperature, the voltage output of the EGT or CHT probe metals’ hot junction (either J or K type thermocouples).  Are you looking to put in a different instrument to read those temps?

 

Cheers,

Jay

 

From: main@Q-List.groups.io <main@Q-List.groups.io> On Behalf Of Bruce Crain
Sent: Thursday, May 28, 2020 5:14 PM
To: main@Q-List.groups.io
Subject: Re: [Q-List] Firewall electric thru connections

 

I suppose it is free standing?  It is fairly old but has a toggle switching between egt/cht and each probe has two designated wires going all the way from the head to the probe.

Bruce

---------- Original Message ----------
From: "Jay Scheevel" <jay@...>
To: main@Q-List.groups.io
Subject: Re: [Q-List] Firewall electric thru connections
Date: Thu, 28 May 2020 16:49:34 -0600

Can you send a picture of your gauge? Is it free standing with only inputs being the two thermocouple wires?

 

Sent from my Verizon Wireless 4G LTE DROID



Bruce Crain <jcrain2@...> wrote:

If the instrument is “amplified signal” such as KN egt/cht gauge will it make a difference?  The material coming out of the KN instrument is the same wire as the probe wires.

Bruce

 

 

On May 28, 2020, at 9:39 AM, Jay Scheevel <jay@...> wrote:

Corrections for connectors of differing metals are difficult to do unless you know the temperatures on both sides of the junction in real time. This is practically impossible, since you would have instrument both sides of the connector with more thermocouples. Any two dissimilar metal junctions respond to temperature with a unique function. If you have, say a copper connector under the firewall, one end of the copper adds a temperature dependent voltage and the other end reduces the voltage same amount, but only if both ends are at the same temperature. So that is the reason for the problem crossing the firewall. The connection calibration at the instrument or engine monitoring box is built in to the software so is predictable and transparent to the user.

 

I am attaching some info on how I did my firewall connectors for EGT and CHT. I have 6 cylinders, so I built up two plugs, each carrying 3 EGT’s and 3 CHT’s, one set on the left and one on the right (see last photo below). The first pic below is on the front of the firewall, right side. This is before I connected the wires into the individual plugs, but you can see the 6 holes for them in the aluminum “container” that I built to contain all 6 individual male plugs. When you disconnect the plug from the firewall, there are 12 prongs! The second pic is on the back side of the firewall. There is no aluminum “container” on this side since they are held down by the two phenolic blocks on either side of the hole. The 6 separate two-prong plugs have a convenient hole in the housing that allowed me to put piece of welding rod through them 3 at a time and gang them together. The ends of the welding rod are clamped to firewall by the phenolic blocks. The black screw heads on the firewall side (first photo) go through the firewall into threaded holes in the phenolic on the back side to secure the plug in place and seal the hole. I am loading the spec sheet for the connectors and some Nuckolls article on thermocouples into the files section, if you want more info.

 

Cheers,

Jay Scheevel, Tri-Q2 N8WQ, 92 hours

<image002.jpg>

<image006.jpg>

<image008.jpg>

From: main@Q-List.groups.io <main@Q-List.groups.io> On Behalf Of Joe Hood
Sent: Thursday, May 28, 2020 6:20 AM
To: main@Q-List.groups.io
Subject: Re: [Q-List] Firewall electric thru connections

 

I used to enjoy wiring up Canon plugs on A-4s. Had no idea on the dissimilar metals and "cold junctions." Can't the instrument be re-calibrated?

 

Found a pretty good primer on thermocouple extensions here (I learn something new every day):

https://www.omega.com/en-us/resources/thermocouple-wire

 

 

Bruce Crain
 

wink_smile Ha!  Nope!  All of this came about because Imraan and I were discussing this topic.  Now you know that I was asking for Imraan (although he wasn't really interested) because he didn't want to have all of the opinions show up.  I let him know everyone has opinions just like belly buttons and he didn't want to see the belly buttons.  So here we are....I am not skeered o' belly buttons.  We did get it hashed out tho' didn't we?  Not sure if Imraan is watching but if he is show him your's.  teeth_smile
Bruce Crain


---------- Original Message ----------
From: "Jay Scheevel" <jay@...>
To: <main@Q-List.groups.io>
Subject: Re: [Q-List] Firewall electric thru connections
Date: Thu, 28 May 2020 17:22:19 -0600

Then that instrument is essentially a voltage meter (with a selector switch), that is calibrated to directly read in Degrees/Temperature, the voltage output of the EGT or CHT probe metals’ hot junction (either J or K type thermocouples).  Are you looking to put in a different instrument to read those temps?

 

Cheers,

Jay

 

From: main@Q-List.groups.io <main@Q-List.groups.io> On Behalf Of Bruce Crain
Sent: Thursday, May 28, 2020 5:14 PM
To: main@Q-List.groups.io
Subject: Re: [Q-List] Firewall electric thru connections

 

I suppose it is free standing?  It is fairly old but has a toggle switching between egt/cht and each probe has two designated wires going all the way from the head to the probe.

Bruce

---------- Original Message ----------
From: "Jay Scheevel" <jay@...>
To: main@Q-List.groups.io
Subject: Re: [Q-List] Firewall electric thru connections
Date: Thu, 28 May 2020 16:49:34 -0600

Can you send a picture of your gauge? Is it free standing with only inputs being the two thermocouple wires?

 

Sent from my Verizon Wireless 4G LTE DROID



Bruce Crain <jcrain2@...> wrote:

If the instrument is “amplified signal” such as KN egt/cht gauge will it make a difference?  The material coming out of the KN instrument is the same wire as the probe wires.

Bruce

 

 

On May 28, 2020, at 9:39 AM, Jay Scheevel <jay@...> wrote:

Corrections for connectors of differing metals are difficult to do unless you know the temperatures on both sides of the junction in real time. This is practically impossible, since you would have instrument both sides of the connector with more thermocouples. Any two dissimilar metal junctions respond to temperature with a unique function. If you have, say a copper connector under the firewall, one end of the copper adds a temperature dependent voltage and the other end reduces the voltage same amount, but only if both ends are at the same temperature. So that is the reason for the problem crossing the firewall. The connection calibration at the instrument or engine monitoring box is built in to the software so is predictable and transparent to the user.

 

I am attaching some info on how I did my firewall connectors for EGT and CHT. I have 6 cylinders, so I built up two plugs, each carrying 3 EGT’s and 3 CHT’s, one set on the left and one on the right (see last photo below). The first pic below is on the front of the firewall, right side. This is before I connected the wires into the individual plugs, but you can see the 6 holes for them in the aluminum “container” that I built to contain all 6 individual male plugs. When you disconnect the plug from the firewall, there are 12 prongs! The second pic is on the back side of the firewall. There is no aluminum “container” on this side since they are held down by the two phenolic blocks on either side of the hole. The 6 separate two-prong plugs have a convenient hole in the housing that allowed me to put piece of welding rod through them 3 at a time and gang them together. The ends of the welding rod are clamped to firewall by the phenolic blocks. The black screw heads on the firewall side (first photo) go through the firewall into threaded holes in the phenolic on the back side to secure the plug in place and seal the hole. I am loading the spec sheet for the connectors and some Nuckolls article on thermocouples into the files section, if you want more info.

 

Cheers,

Jay Scheevel, Tri-Q2 N8WQ, 92 hours

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From: main@Q-List.groups.io <main@Q-List.groups.io> On Behalf Of Joe Hood
Sent: Thursday, May 28, 2020 6:20 AM
To: main@Q-List.groups.io
Subject: Re: [Q-List] Firewall electric thru connections

 

I used to enjoy wiring up Canon plugs on A-4s. Had no idea on the dissimilar metals and "cold junctions." Can't the instrument be re-calibrated?

 

Found a pretty good primer on thermocouple extensions here (I learn something new every day):

https://www.omega.com/en-us/resources/thermocouple-wire

 

 

 


Rik
 

Doesn’t everyone know what a canon plug connector is? The thermocouple wires are connected via a cannon plug on every turbine I’ve had along with the tach generator, temp sensor, frag’s etc.. 

You can pick these up used at an aircraft supply place like ET Supply in LA. as well as many other supply places. 

Jay Scheevel
 

I think that is what Corbin showed a picture of and the MIL spec part number for. Am I wrong?

Jay

Sent from my Verizon Wireless 4G LTE DROID


Rik <Info@...> wrote:

Doesn’t everyone know what a canon plug connector is? The thermocouple wires are connected via a cannon plug on every turbine I’ve had along with the tach generator, temp sensor, frag’s etc.. 

You can pick these up used at an aircraft supply place like ET Supply in LA. as well as many other supply places.