Thermocouple compatible bulkhead connector?


John Loram <johnl@...>
 

Does any one know of a source (other than Omega) for multi-pin bulkhead
connectors that are compatible with Type J & K thermocouples? I wiring the
firewall foreword...

thanks, -john-


Sam Hoskins
 

I just used a metal D-sub connector. Bob Knuckolls said it was okay to use.

Sam Hoskins


On Wed, Feb 3, 2010 at 4:59 PM, John Loram <johnl@loram.org> wrote:



Does any one know of a source (other than Omega) for multi-pin bulkhead
connectors that are compatible with Type J & K thermocouples? I wiring the
firewall foreword...

thanks, -john-

[Non-text portions of this message have been removed]



[Non-text portions of this message have been removed]


Jay Scheevel <scheevel@...>
 

Hi John,

I get all my connectors and electronic components from Newark. (Newark.com)

Cheers,
Jay


John Loram <johnl@...>
 

Thanks for that Sam. Your comment forced me to rethink the problem and I
realized that I had not considered that I was running both sides of each
thermocouple leg through the same connector (duh!), and consequently, the
effect of the dissimilar metals of the connector would be cancelled out so
long as both the male and the female pins of the connector are the same
material.

Cool! thanks again, -john-

-----Original Message-----
From: Q-LIST@yahoogroups.com [mailto:Q-LIST@yahoogroups.com]
On Behalf Of Sam Hoskins
Sent: Thursday, February 04, 2010 5:40 AM
To: Q-LIST
Subject: Re: [Q-LIST] Thermocouple compatible bulkhead connector?

I just used a metal D-sub connector. Bob Knuckolls said it
was okay to use.

Sam Hoskins


On Wed, Feb 3, 2010 at 4:59 PM, John Loram <johnl@loram.org> wrote:



Does any one know of a source (other than Omega) for multi-pin
bulkhead connectors that are compatible with Type J & K
thermocouples?
I wiring the firewall foreword...

thanks, -john-









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Rick Hole
 

I was curious about this as in theory the additional dissimilar metal junction will cause errors in the readings. As an experiment I tried connecting a type K thermocouple to a digital thermometer readout with a length of copper wire spliced in. With the thermocouple immersed in a hot oil bath I watched the temperature displayed as I used a hot air gun to heat the junction of copper to thermocouple wire. I thought I could see 1-2 degrees change heating the junction from ambient to as hot as the gun would deliver, but it was difficult to tell the change from random drift.

I have forgotten if I repeated the experiment with a type J thermocouple. The metals involved are different and I would not assume the same results without testing.

So my conclusion is, for type K as used in EGT probes and often used for CHT, you can use the non-thermocouple connector or even use copper extension wire without significant error. And as long as all the cylinder's wires are the same temperature at the change of metal, all the errors are the same magnitude and direction, so with EGTs where only the trend is important, you are doubly ok.

Rick Hole

--- In Q-LIST@yahoogroups.com, "John Loram" <johnl@...> wrote:

Thanks for that Sam. Your comment forced me to rethink the problem and I
realized that I had not considered that I was running both sides of each
thermocouple leg through the same connector (duh!), and consequently, the
effect of the dissimilar metals of the connector would be cancelled out so
long as both the male and the female pins of the connector are the same
material.

Cool! thanks again, -john-


John Loram <johnl@...>
 

Hi Rick:
When you splice a connector into a thermocouple wire, you actually create
two junctions (the point I missed ): one junction is created where the
thermocouple wire is attached to the plug side of the connector, and a
second junction is create where you connect the thermocouple wire to the
socket side of the connector. These two junctions are of opposite polarity,
so, if the two junctions are at the same temperature (as they would be since
they are plugged into one another) they electrically balance out one another
and will have no effect on the temperature measurement.

building like crazy, -john-
www.loram.org




_____

From: Q-LIST@yahoogroups.com [mailto:Q-LIST@yahoogroups.com] On Behalf Of
Rick
Sent: Thursday, February 04, 2010 3:11 PM
To: Q-LIST@yahoogroups.com
Subject: [Q-LIST] Re: Thermocouple compatible bulkhead connector?




I was curious about this as in theory the additional dissimilar metal
junction will cause errors in the readings. As an experiment I tried
connecting a type K thermocouple to a digital thermometer readout with a
length of copper wire spliced in. With the thermocouple immersed in a hot
oil bath I watched the temperature displayed as I used a hot air gun to heat
the junction of copper to thermocouple wire. I thought I could see 1-2
degrees change heating the junction from ambient to as hot as the gun would
deliver, but it was difficult to tell the change from random drift.

I have forgotten if I repeated the experiment with a type J thermocouple.
The metals involved are different and I would not assume the same results
without testing.

So my conclusion is, for type K as used in EGT probes and often used for
CHT, you can use the non-thermocouple connector or even use copper extension
wire without significant error. And as long as all the cylinder's wires are
the same temperature at the change of metal, all the errors are the same
magnitude and direction, so with EGTs where only the trend is important, you
are doubly ok.

Rick Hole

--- In Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com, "John
Loram" <johnl@...> wrote:

Thanks for that Sam. Your comment forced me to rethink the problem and I
realized that I had not considered that I was running both sides of each
thermocouple leg through the same connector (duh!), and consequently, the
effect of the dissimilar metals of the connector would be cancelled out so
long as both the male and the female pins of the connector are the same
material.

Cool! thanks again, -john-


Rick Hole
 

Yes, but note that in a firewall connector you will expect a higher temperature on the engine side compared to the cabin side. There will be an error but it really is not significant. Even if you use the bulkhead connector as the point where you convert the thermocouple metal wires into copper (and you will do this somewhere, at least at the instrument) and error will ocurr. If high accuracy is required, a second thermocouple is placed at the junction to copper for "cold junction" compensation. But we do not require that level of precision. EGTs are relative, and CHTs, well, if I am operating say 5 degrees from red line I will already have taken action.

Rick

--- In Q-LIST@yahoogroups.com, "John Loram" <johnl@...> wrote:

Hi Rick:
When you splice a connector into a thermocouple wire, you actually create
two junctions (the point I missed ): one junction is created where the
thermocouple wire is attached to the plug side of the connector, and a
second junction is create where you connect the thermocouple wire to the
socket side of the connector. These two junctions are of opposite polarity,
so, if the two junctions are at the same temperature (as they would be since
they are plugged into one another) they electrically balance out one another
and will have no effect on the temperature measurement.

building like crazy, -john-
www.loram.org




_____

From: Q-LIST@yahoogroups.com [mailto:Q-LIST@yahoogroups.com] On Behalf Of
Rick
Sent: Thursday, February 04, 2010 3:11 PM
To: Q-LIST@yahoogroups.com
Subject: [Q-LIST] Re: Thermocouple compatible bulkhead connector?




I was curious about this as in theory the additional dissimilar metal
junction will cause errors in the readings. As an experiment I tried
connecting a type K thermocouple to a digital thermometer readout with a
length of copper wire spliced in. With the thermocouple immersed in a hot
oil bath I watched the temperature displayed as I used a hot air gun to heat
the junction of copper to thermocouple wire. I thought I could see 1-2
degrees change heating the junction from ambient to as hot as the gun would
deliver, but it was difficult to tell the change from random drift.

I have forgotten if I repeated the experiment with a type J thermocouple.
The metals involved are different and I would not assume the same results
without testing.

So my conclusion is, for type K as used in EGT probes and often used for
CHT, you can use the non-thermocouple connector or even use copper extension
wire without significant error. And as long as all the cylinder's wires are
the same temperature at the change of metal, all the errors are the same
magnitude and direction, so with EGTs where only the trend is important, you
are doubly ok.

Rick Hole

--- In Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com, "John
Loram" <johnl@> wrote:

Thanks for that Sam. Your comment forced me to rethink the problem and I
realized that I had not considered that I was running both sides of each
thermocouple leg through the same connector (duh!), and consequently, the
effect of the dissimilar metals of the connector would be cancelled out so
long as both the male and the female pins of the connector are the same
material.

Cool! thanks again, -john-






[Non-text portions of this message have been removed]


John Loram <johnl@...>
 

Given that the pins in a connector are in such intimate contact, I'd be
surprised to learn that there's even one degree of temperature difference
between the junctions; less than the resolution of the measuring system.

It's my impression that all the modern electronic engine monitors
incorporate cold junction compensation within the instrument; it's done with
a thermistor and a few lines of code.

-john-


_____

From: Q-LIST@yahoogroups.com [mailto:Q-LIST@yahoogroups.com] On Behalf Of
Rick
Sent: Thursday, February 04, 2010 5:07 PM
To: Q-LIST@yahoogroups.com
Subject: [Q-LIST] Re: Thermocouple compatible bulkhead connector?




Yes, but note that in a firewall connector you will expect a higher
temperature on the engine side compared to the cabin side. There will be an
error but it really is not significant. Even if you use the bulkhead
connector as the point where you convert the thermocouple metal wires into
copper (and you will do this somewhere, at least at the instrument) and
error will ocurr. If high accuracy is required, a second thermocouple is
placed at the junction to copper for "cold junction" compensation. But we do
not require that level of precision. EGTs are relative, and CHTs, well, if I
am operating say 5 degrees from red line I will already have taken action.

Rick

--- In Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com, "John
Loram" <johnl@...> wrote:

Hi Rick:
When you splice a connector into a thermocouple wire, you actually create
two junctions (the point I missed ): one junction is created where the
thermocouple wire is attached to the plug side of the connector, and a
second junction is create where you connect the thermocouple wire to the
socket side of the connector. These two junctions are of opposite
polarity,
so, if the two junctions are at the same temperature (as they would be
since
they are plugged into one another) they electrically balance out one
another
and will have no effect on the temperature measurement.

building like crazy, -john-
www.loram.org




_____

From: Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com
[mailto:Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com] On Behalf
Of
Rick
Sent: Thursday, February 04, 2010 3:11 PM
To: Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com
Subject: [Q-LIST] Re: Thermocouple compatible bulkhead connector?




I was curious about this as in theory the additional dissimilar metal
junction will cause errors in the readings. As an experiment I tried
connecting a type K thermocouple to a digital thermometer readout with a
length of copper wire spliced in. With the thermocouple immersed in a hot
oil bath I watched the temperature displayed as I used a hot air gun to
heat
the junction of copper to thermocouple wire. I thought I could see 1-2
degrees change heating the junction from ambient to as hot as the gun
would
deliver, but it was difficult to tell the change from random drift.

I have forgotten if I repeated the experiment with a type J thermocouple.
The metals involved are different and I would not assume the same results
without testing.

So my conclusion is, for type K as used in EGT probes and often used for
CHT, you can use the non-thermocouple connector or even use copper
extension
wire without significant error. And as long as all the cylinder's wires
are
the same temperature at the change of metal, all the errors are the same
magnitude and direction, so with EGTs where only the trend is important,
you
are doubly ok.

Rick Hole

--- In Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com, "John
Loram" <johnl@> wrote:

Thanks for that Sam. Your comment forced me to rethink the problem and I
realized that I had not considered that I was running both sides of each
thermocouple leg through the same connector (duh!), and consequently,
the
effect of the dissimilar metals of the connector would be cancelled out
so
long as both the male and the female pins of the connector are the same
material.

Cool! thanks again, -john-








Rick Hole
 

The high end ones certainly do, such as Garmin 900X or 1000. I have not
seen anything in the Dynons, GRT Avionics, JPI, etc that I have dealt with
in recent years to indicate they compensate. Or if they do it must be
internal rather than in the external connector where it really belongs. But
on the point, the precision of these instruments is well within what we need
to operate the engine effectively and safely.



Garmin engineers are upset if non-thermocouple connector pins are used and
insist this not be done (G900X installs). I agree with you, it is overkill
and over-expensive.



_____

From: Q-LIST@yahoogroups.com [mailto:Q-LIST@yahoogroups.com] On Behalf Of
John Loram
Sent: Thursday, February 04, 2010 8:28 PM
To: Q-LIST@yahoogroups.com
Subject: RE: [Q-LIST] Re: Thermocouple compatible bulkhead connector?





Given that the pins in a connector are in such intimate contact, I'd be
surprised to learn that there's even one degree of temperature difference
between the junctions; less than the resolution of the measuring system.

It's my impression that all the modern electronic engine monitors
incorporate cold junction compensation within the instrument; it's done with
a thermistor and a few lines of code.

-john-

_____