Re: Firewall electric thru connections


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

 

 

 


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