Well, I did a thing, It was a thing I knew better then to do, too. (Thermocouple connecting) |
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Well, I did a thing, It was a thing I knew better then to do, too. (Thermocouple connecting) |
iankarr |
Oct 12 2023, 11:20 PM
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#21
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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?
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Shivers |
Oct 13 2023, 12:40 AM
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#22
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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
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Superhawk996 |
Oct 13 2023, 07:10 AM
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#23
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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 |
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. |
Spoke |
Oct 13 2023, 07:40 AM
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#24
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Jerry Group: Members Posts: 7,079 Joined: 29-October 04 From: Allentown, PA Member No.: 3,031 Region Association: None |
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? |
Superhawk996 |
Oct 13 2023, 07:52 AM
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#25
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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 |
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. |
76-914 |
Oct 13 2023, 07:56 AM
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#26
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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 |
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76-914 |
Oct 13 2023, 08:10 AM
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#27
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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???
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Literati914 |
Oct 13 2023, 08:49 AM
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#28
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Senior Member Group: Members Posts: 1,697 Joined: 16-November 06 From: Dallas, TX Member No.: 7,222 Region Association: Southwest Region |
... 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? . |
Superhawk996 |
Oct 13 2023, 09:15 AM
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#29
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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 |
... 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). |
worn |
Oct 13 2023, 05:54 PM
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#30
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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.
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76-914 |
Oct 13 2023, 05:58 PM
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#31
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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 |
... 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. |
76-914 |
Oct 13 2023, 06:02 PM
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#32
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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 |
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) |
Literati914 |
Oct 13 2023, 10:32 PM
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#33
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Senior Member Group: Members Posts: 1,697 Joined: 16-November 06 From: Dallas, TX Member No.: 7,222 Region Association: Southwest Region |
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) |
VaccaRabite |
Oct 14 2023, 10:08 AM
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#34
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En Garde! Group: Admin Posts: 13,584 Joined: 15-December 03 From: Dallastown, PA Member No.: 1,435 Region Association: MidAtlantic Region |
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 |
sixnotfour |
Oct 14 2023, 10:31 AM
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#35
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914 Wizard Group: Members Posts: 10,598 Joined: 12-September 04 From: Life Elevated..planet UT. Member No.: 2,744 Region Association: Rocky Mountains |
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) |
Literati914 |
Oct 14 2023, 12:01 PM
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#36
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Senior Member Group: Members Posts: 1,697 Joined: 16-November 06 From: Dallas, TX Member No.: 7,222 Region Association: Southwest Region |
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) . |
stownsen914 |
Oct 14 2023, 03:28 PM
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#37
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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?
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Superhawk996 |
Oct 14 2023, 07:01 PM
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#38
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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 |
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 |
stownsen914 |
Oct 15 2023, 08:44 AM
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#39
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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 |
Superhawk996 |
Oct 15 2023, 11:09 AM
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#40
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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 |
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. |
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