Home  |  Forums  |  914 Info  |  Blogs
 
914World.com - The fastest growing online 914 community!
 
Porsche, and the Porsche crest are registered trademarks of Dr. Ing. h.c. F. Porsche AG. This site is not affiliated with Porsche in any way.
Its only purpose is to provide an online forum for car enthusiasts. All other trademarks are property of their respective owners.
 

Welcome Guest ( Log In | Register )

3 Pages V < 1 2 3 >  
Reply to this topicStart new topic
> Well, I did a thing, It was a thing I knew better then to do, too. (Thermocouple connecting)
iankarr
post Oct 12 2023, 11:20 PM
Post #21


The wrencher formerly known as Cuddy_K
****

Group: Members
Posts: 2,519
Joined: 22-May 15
From: Heber City, UT
Member No.: 18,749
Region Association: Intermountain Region



Is there any difference in the makeup of that extension wire? I mean, is the positive wire a different metal, etc. Or are the red and yellow sides the same and just color-coded to make sure it hooks up to the thermocouple correctly?
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Shivers
post Oct 13 2023, 12:40 AM
Post #22


Senior Member
****

Group: Members
Posts: 2,758
Joined: 19-October 20
From: La Quinta, CA
Member No.: 24,781
Region Association: Southern California



K Type Thermocouple positive leg is composed of 90% nickel, 10%chromium and a negative leg is composed of 95% nickel, 2% aluminum, 2% manganese and 1% silicon
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Superhawk996
post Oct 13 2023, 07:10 AM
Post #23


914 Guru
*****

Group: Members
Posts: 6,502
Joined: 25-August 18
From: Woods of N. Idaho
Member No.: 22,428
Region Association: Galt's Gulch



QUOTE(iankarr @ Oct 13 2023, 01:20 AM) *

Is there any difference in the makeup of that extension wire? I mean, is the positive wire a different metal, etc. Or are the red and yellow sides the same and just color-coded to make sure it hooks up to the thermocouple correctly?


Yes, the thermocouple extension wires are made of different materials between the positive (yellow) and the negative (red) wires.

Thermocouple extension wire is very similar to the sensing wire, but uses less of the expensive metals (Nickel, Chromium,etc.) content in its construction to keep cost lower. However, the overall characteristics of the extension wire are still very close to the sensing wire and are VERY different from simple copper wire. Because the extension wire is slightly different than the sensing wire - its use comes with some constraints such as a more limited range of operation temperature. Example: Extension wire needs to be kept below 200C (not a problem for 914 application) and you want the temperature across the thermocouple extension (end to end) wire to be as uniform as possible.

Introduction of a third metal (like copper extension wire or copper/tin connector terminals) into the circuit will add a 3rd temperature junction that is uncompensated and will affect the accuracy and calibration of the thermocouple.

@Iankarr

Thermocouple extension wire also has different temperature limits and tolerance than the sensing wire. There are more expensive grades of extension wire that are used when higher accuracy is needed (doesn’t apply to our application).

When I used to do data acquisition, it wasn't uncommon to have to run long thermocouple extensions from the test cell into a control room - sometimes 75' or so. It would get expensive stringing sensing wire the whole way - especially when you may have 40 or 50 thermouple channels under test. In the case of our 914's that distance from the engine to the cabin in really only 5 feet so using sensing wire the whole way wouldn't be unreasonable.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Spoke
post Oct 13 2023, 07:40 AM
Post #24


Jerry
*****

Group: Members
Posts: 7,079
Joined: 29-October 04
From: Allentown, PA
Member No.: 3,031
Region Association: None



QUOTE(Shivers @ Oct 13 2023, 02:40 AM) *

K Type Thermocouple positive leg is composed of 90% nickel, 10%chromium and a negative leg is composed of 95% nickel, 2% aluminum, 2% manganese and 1% silicon


Question would be how far away from the joining of the 2 dissimilar metals can the 2 leads change to one type of conductor maybe not made of the same materials as either dissimilar metals?

When the thermocouple is connected to the gauge, both metals change to the type of metal found on PCBs. So somewhere away from the dissimilar joint it is ok to use different metals. Where is that point?
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Superhawk996
post Oct 13 2023, 07:52 AM
Post #25


914 Guru
*****

Group: Members
Posts: 6,502
Joined: 25-August 18
From: Woods of N. Idaho
Member No.: 22,428
Region Association: Galt's Gulch



QUOTE(Spoke @ Oct 13 2023, 09:40 AM) *

QUOTE(Shivers @ Oct 13 2023, 02:40 AM) *

K Type Thermocouple positive leg is composed of 90% nickel, 10%chromium and a negative leg is composed of 95% nickel, 2% aluminum, 2% manganese and 1% silicon


Question would be how far away from the joining of the 2 dissimilar metals can the 2 leads change to one type of conductor maybe not made of the same materials as either dissimilar metals?

When the thermocouple is connected to the gauge, both metals change to the type of metal found on PCBs. So somewhere away from the dissimilar joint it is ok to use different metals. Where is that point?


Anywhere two dissimilar metals join will become a new temperature sensing junction with it's own EMF produced at that junction.

In the case of attachment at the gauge, this is the cold junction and it is compensated.

If a dissimilar metal is introduced somewhere between the hot junction and the cold junction it too could be compensated (if temperature at that junction is known) but often that junction will be highly non-linear and would make it tough to compensate for.

I think the thing that throws people on thermocouples is that the sensing is not due to resistance change but due to the Seebeck effect that generates its own voltage potential between the two dissimilar metals as temperature changes. Resistance only begins to come into play when extension cables become very long (100' or so). I'm not saying resistance doesn't matter . . . just that resistance change isn't what drives the operation of a thermocouple.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
76-914
post Oct 13 2023, 07:56 AM
Post #26


Repeat Offender & Resident Subaru Antagonist
**********

Group: Members
Posts: 13,621
Joined: 23-January 09
From: Temecula, CA
Member No.: 9,964
Region Association: Southern California



QUOTE(stownsen914 @ Oct 12 2023, 09:28 PM) *

QUOTE(Geezer914 @ Oct 12 2023, 05:52 PM) *

Did this work with a Dakota Digital gauge?



I have a similar question ... will the cheap thermocouple work with a VDO CHT gauge.

Yes. See post #5
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
76-914
post Oct 13 2023, 08:10 AM
Post #27


Repeat Offender & Resident Subaru Antagonist
**********

Group: Members
Posts: 13,621
Joined: 23-January 09
From: Temecula, CA
Member No.: 9,964
Region Association: Southern California



Let's flip things around. Guess what happens if power is applied to a thermocouple? If you figured that out guess what happens if you reverse that current???
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Literati914
post Oct 13 2023, 08:49 AM
Post #28


Senior Member
***

Group: Members
Posts: 1,697
Joined: 16-November 06
From: Dallas, TX
Member No.: 7,222
Region Association: Southwest Region



QUOTE(76-914 @ Oct 11 2023, 09:13 AM) *

... I had suspected the VDO gauge but as it turned out the VDO gauge performed well when coupled, no pun intended, to the Dakota sender.


Wait are you saying that the analog VDO gauge reads correctly (it’s got a reputation for being off) when using the Dakota thermocoupling wire & ring? Meaning that the wire is actually the compensated part of the puzzle? Or are you just saying that it fires up and “works” in general? I was wondering this a few weeks ago when I purchased the complete dakota setup while really wanting the VDO to be a more viable solution. Sorry to be so dense, but can you confirm?


.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Superhawk996
post Oct 13 2023, 09:15 AM
Post #29


914 Guru
*****

Group: Members
Posts: 6,502
Joined: 25-August 18
From: Woods of N. Idaho
Member No.: 22,428
Region Association: Galt's Gulch



QUOTE(Literati914 @ Oct 13 2023, 10:49 AM) *

QUOTE(76-914 @ Oct 11 2023, 09:13 AM) *

... I had suspected the VDO gauge but as it turned out the VDO gauge performed well when coupled, no pun intended, to the Dakota sender.


Wait are you saying that the analog VDO gauge reads correctly (it’s got a reputation for being off) when using the Dakota thermocoupling wire & ring? Meaning that the wire is actually the compensated part of the puzzle? Or are you just saying that it fires up and “works” in general? I was wondering this a few weeks ago when I purchased the complete dakota setup while really wanting the VDO to be a more viable solution. Sorry to be so dense, but can you confirm?


.


Both use the same K-type thermocouple sensor.


VDO is an uncompensated cold junction - its just basically a milli-volt meter with a gauge face that is calibrated to cylinder head temperature. It assumes the cold junction ambient temp is 68F (maybe 70F??) if I recall. This is why VDO has more error.

Dakota Digital is compensated cold junction and is more accurate. Internally, it measures the temperature of the cold junction and applies a correction to the displayed value based on the ambient temperature at the gauge (i.e. the cold junction).
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
worn
post Oct 13 2023, 05:54 PM
Post #30


can't remember
****

Group: Members
Posts: 3,323
Joined: 3-June 11
From: Madison, WI
Member No.: 13,152
Region Association: Upper MidWest



Getting the spark plug and ring out has always seemed such a major PITA. If you come up with a disconnect solution it will be a service to us all.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
76-914
post Oct 13 2023, 05:58 PM
Post #31


Repeat Offender & Resident Subaru Antagonist
**********

Group: Members
Posts: 13,621
Joined: 23-January 09
From: Temecula, CA
Member No.: 9,964
Region Association: Southern California



QUOTE(Literati914 @ Oct 13 2023, 07:49 AM) *

QUOTE(76-914 @ Oct 11 2023, 09:13 AM) *

... I had suspected the VDO gauge but as it turned out the VDO gauge performed well when coupled, no pun intended, to the Dakota sender.


Wait are you saying that the analog VDO gauge reads correctly (it’s got a reputation for being off) when using the Dakota thermocoupling wire & ring? Meaning that the wire is actually the compensated part of the puzzle? Or are you just saying that it fires up and “works” in general? I was wondering this a few weeks ago when I purchased the complete dakota setup while really wanting the VDO to be a more viable solution. Sorry to be so dense, but can you confirm?


.

Yes. I had a post 10-12 years ago here showing the results. I used heated oil since it won't cool as quickly as water. IIRC, I compared the VDO setup vs the Dakota setup and finally tested the VDO with the 12ft long Dakota lead & sender. Try it and let me know your results.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
76-914
post Oct 13 2023, 06:02 PM
Post #32


Repeat Offender & Resident Subaru Antagonist
**********

Group: Members
Posts: 13,621
Joined: 23-January 09
From: Temecula, CA
Member No.: 9,964
Region Association: Southern California



QUOTE(worn @ Oct 13 2023, 04:54 PM) *

Getting the spark plug and ring out has always seemed such a major PITA. If you come up with a disconnect solution it will be a service to us all.

The OD of the ring can be gently filed down so that it slips into the round plug receptacle. I used a flat file from a needle file set because it was less aggressive. The material is very soft so do so with care. (IMG:style_emoticons/default/beerchug.gif)
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Literati914
post Oct 13 2023, 10:32 PM
Post #33


Senior Member
***

Group: Members
Posts: 1,697
Joined: 16-November 06
From: Dallas, TX
Member No.: 7,222
Region Association: Southwest Region



QUOTE(worn @ Oct 13 2023, 06:54 PM) *

Getting the spark plug and ring out has always seemed such a major PITA. If you come up with a disconnect solution it will be a service to us all.


I’m confused as to why not leave the ring under the sparkplug and just unscrew the two small connecting screws that are about a ft. down the line (IMG:style_emoticons/default/confused24.gif)
Here’s my DD lead wire:


Attached image(s)
Attached Image
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
VaccaRabite
post Oct 14 2023, 10:08 AM
Post #34


En Garde!
**********

Group: Admin
Posts: 13,584
Joined: 15-December 03
From: Dallastown, PA
Member No.: 1,435
Region Association: MidAtlantic Region



QUOTE(Literati914 @ Oct 14 2023, 12:32 AM) *

QUOTE(worn @ Oct 13 2023, 06:54 PM) *

Getting the spark plug and ring out has always seemed such a major PITA. If you come up with a disconnect solution it will be a service to us all.


I’m confused as to why not leave the ring under the sparkplug and just unscrew the two small connecting screws that are about a ft. down the line (IMG:style_emoticons/default/confused24.gif)
Here’s my DD lead wire:

There are a couple reasons:
1) it’s common to put some heat shrink tube over the screws to protect them and keep them in place when driving. Which just adds another barrier to getting at them.

2) I also have mine routed under the tin (fairly common) so you can’t get to the screws anyway. They are hidden under the cooling tin. There tend to be a lot of wires and hoses on the 3/4 side of the car next to the battery, and this gets the TC wire out of the way.

3) those tiny screws are a PITA to handle and tend to get swallowed up in the engine bay when you inevitably drop one.
Zach
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
sixnotfour
post Oct 14 2023, 10:31 AM
Post #35


914 Wizard
**********

Group: Members
Posts: 10,598
Joined: 12-September 04
From: Life Elevated..planet UT.
Member No.: 2,744
Region Association: Rocky Mountains



QUOTE(VaccaRabite @ Oct 14 2023, 10:08 AM) *

QUOTE(Literati914 @ Oct 14 2023, 12:32 AM) *

QUOTE(worn @ Oct 13 2023, 06:54 PM) *

Getting the spark plug and ring out has always seemed such a major PITA. If you come up with a disconnect solution it will be a service to us all.


I’m confused as to why not leave the ring under the sparkplug and just unscrew the two small connecting screws that are about a ft. down the line (IMG:style_emoticons/default/confused24.gif)
Here’s my DD lead wire:

There are a couple reasons:
1) it’s common to put some heat shrink tube over the screws to protect them and keep them in place when driving. Which just adds another barrier to getting at them.

2) I also have mine routed under the tin (fairly common) so you can’t get to the screws anyway. They are hidden under the cooling tin. There tend to be a lot of wires and hoses on the 3/4 side of the car next to the battery, and this gets the TC wire out of the way.

3) those tiny screws are a PITA to handle and tend to get swallowed up in the engine bay when you inevitably drop one.
Zach


Uh Hu.... (IMG:style_emoticons/default/happy11.gif)
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Literati914
post Oct 14 2023, 12:01 PM
Post #36


Senior Member
***

Group: Members
Posts: 1,697
Joined: 16-November 06
From: Dallas, TX
Member No.: 7,222
Region Association: Southwest Region



QUOTE(sixnotfour @ Oct 14 2023, 11:31 AM) *

QUOTE(VaccaRabite @ Oct 14 2023, 10:08 AM) *

QUOTE(Literati914 @ Oct 14 2023, 12:32 AM) *

QUOTE(worn @ Oct 13 2023, 06:54 PM) *

Getting the spark plug and ring out has always seemed such a major PITA. If you come up with a disconnect solution it will be a service to us all.


I’m confused as to why not leave the ring under the sparkplug and just unscrew the two small connecting screws that are about a ft. down the line (IMG:style_emoticons/default/confused24.gif)
Here’s my DD lead wire:

There are a couple reasons:
1) it’s common to put some heat shrink tube over the screws to protect them and keep them in place when driving. Which just adds another barrier to getting at them.

2) I also have mine routed under the tin (fairly common) so you can’t get to the screws anyway. They are hidden under the cooling tin. There tend to be a lot of wires and hoses on the 3/4 side of the car next to the battery, and this gets the TC wire out of the way.

3) those tiny screws are a PITA to handle and tend to get swallowed up in the engine bay when you inevitably drop one.
Zach


Uh Hu.... (IMG:style_emoticons/default/happy11.gif)


Note to self: route TC wire above the tin and use a magnetic screwdriver, got it, thanks (IMG:style_emoticons/default/poke.gif)

.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
stownsen914
post Oct 14 2023, 03:28 PM
Post #37


Senior Member
***

Group: Members
Posts: 928
Joined: 3-October 06
From: Ossining, NY
Member No.: 6,985
Region Association: None



Is there a way to join a K type thermocouple to a proper extension lead, other than an Omega plug? Are there butt splices made of the correct material?
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Superhawk996
post Oct 14 2023, 07:01 PM
Post #38


914 Guru
*****

Group: Members
Posts: 6,502
Joined: 25-August 18
From: Woods of N. Idaho
Member No.: 22,428
Region Association: Galt's Gulch



QUOTE(stownsen914 @ Oct 14 2023, 05:28 PM) *

Is there a way to join a K type thermocouple to a proper extension lead, other than an Omega plug? Are there butt splices made of the correct material?

I’ve never seen them in years and years of data acquisition testing.

Google search for Chromel butt connector turns up at about $10 and some change per splice, min order 2500, at a cost of $26k, 182 day lead time.

And then you’ll need the other Alumel splices for the negative conductor - let’s assume another $26k minimum order for those.

(IMG:style_emoticons/default/lol-2.gif) how bad do you really need butt splices for thermocouple wires?

Looks like Mouser stocks the Chromel & Alumel ring terminals that Dakota Digital is probably using - you could use those and the screws like Dakota does

Attached Image
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
stownsen914
post Oct 15 2023, 08:44 AM
Post #39


Senior Member
***

Group: Members
Posts: 928
Joined: 3-October 06
From: Ossining, NY
Member No.: 6,985
Region Association: None



Well that makes the Omega plugs looks like a better option (IMG:style_emoticons/default/smile.gif)

One other thing - I have a VDO CHT that's missing the harness and thermocouple. It has what appear to be standard male blade connectors at the gauge. I'm not seeing chromel or alumel female connectors. I guess using copper ones would create an uncompensated junction (if that's the correct term)?

This is making the $60 VDO thermocouple and wiring kit more appealing haha
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Superhawk996
post Oct 15 2023, 11:09 AM
Post #40


914 Guru
*****

Group: Members
Posts: 6,502
Joined: 25-August 18
From: Woods of N. Idaho
Member No.: 22,428
Region Association: Galt's Gulch



QUOTE(stownsen914 @ Oct 15 2023, 10:44 AM) *

Well that makes the Omega plugs looks like a better option (IMG:style_emoticons/default/smile.gif)

One other thing - I have a VDO CHT that's missing the harness and thermocouple. It has what appear to be standard male blade connectors at the gauge. I'm not seeing chromel or alumel female connectors. I guess using copper ones would create an uncompensated junction (if that's the correct term)?

This is making the $60 VDO thermocouple and wiring kit more appealing haha


If I recall the VDO did use plain copper female spade at the gauge. Yes connection to the back of the gauge that is considered the uncompensated cold junction for VDO so that transition from Chromel / Alumel to copper right at the gauge “should” be part of their gauge face calibration.

It’s been a long time since I had a VDO gauge in my hand but in all honesty - it serves a purpose which is to get general trends in cyclinder head temp without fretting over 20F one way or the other due to gauge error.

You’re right though - $60 for an extension, sensing end, and connectors isn’t outrageous in this day vs. sourcing all the bits yourself.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post

3 Pages V < 1 2 3 >
Reply to this topicStart new topic
2 User(s) are reading this topic (2 Guests and 0 Anonymous Users)
0 Members:

 



- Lo-Fi Version Time is now: 31st October 2024 - 05:54 PM