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Paul Eckenroth
Joined: 29 Jun 2010
Posts: 14
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 Posted: Wed Jun 29, 2022 1:31 pm Post subject: Thermocouple wire extension |
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As I redo my Revmaster engine with the burned stator I plan to incorporate thermocouples to hopefully allow me to head off a repeat of the burned stator. In the past on both the RV and the Onex I ran the full length of the suppllied thermocouple wire and then connected to tefzel coated copper for the rest of the run to the EIS using Faston connectors. The temperature read out for both planes seems reasonable and accurate. Although it has never been checked using boiling water. Now that I'm looking into thermocouples again I read that only thermocouple wire should be used for extensions and copper wire should never be used.
So, I am looking for some guidance. Is my prior approach totally faulty producing meaningless temperature readings or are the practices I read about only required for super accurate results and what I have done in the past good enough. I will appreciate any opinions. Thanks.
Paul
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Eric Page
Joined: 15 Feb 2017
Posts: 242
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| Posted: Wed Jun 29, 2022 7:07 pm Post subject: Re: Thermocouple wire extension |
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What follows assumes that you're using Type K thermocouples, which are made from chromel and alumel wires.
You won't be getting dead accurate readings with the copper wire extensions. That said, the amount of error is probably not huge and would be difficult to determine without comparative measurements.
Your extension has created two additional dissimilar-metal junctions in the sensor wires -- one alumel-copper, the other chromel-copper -- which will generate opposing errors of different magnitude that the instrument isn't calibrated for. The total error will depend on the temperature where those junctions are located; the higher the temp, the greater the error.
The easiest and cheapest source of chromel-alumel wire to extend Type-K sensor leads is to buy extra sensors on eBay or Amazon and cut off what you need. Just be careful to match wire types in your extensions so you don't create additional chromel-alumel junctions.
Whatever method you use to splice the extensions, it's important that the wires are in intimate physical contact. They should be crushed against one another and not depending on a third metal to interface between them.
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charlesdavis(at)iuncapped
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| Posted: Wed Jun 29, 2022 9:02 pm Post subject: Thermocouple wire extension |
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With regards extending the chromel/alumel, I have always twisted and
"silver soldered" the connections, and have had no issues. Crimped
connections are a second-best option
On 30/06/22 05:07 am, Eric Page wrote:
| Quote: |
What follows assumes that you're using Type K thermocouples, which are made from chromel and alumel wires.
You won't be getting dead accurate readings with the copper wire extensions. That said, the amount of error is probably not huge and would be difficult to determine without comparative measurements.
Your extension has created two additional dissimilar-metal junctions in the sensor wires -- one alumel-copper, the other chromel-copper -- which will generate opposing errors of different magnitude that the instrument isn't calibrated for. The total error will depend on the temperature where those junctions are located; the higher the temp, the greater the error.
The easiest and cheapest source of chromel-alumel wire to extend Type-K sensor leads is to buy extra sensors on eBay or Amazon and cut off what you need. Just be careful to match wire types in your extensions so you don't create additional chromel-alumel junctions.
Whatever method you use to splice the extensions, it's important that the wires are in intimate physical contact. They should be crushed against one another and not depending on a third metal to interface between them.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=507362#507362
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Ceengland
Joined: 11 Oct 2020
Posts: 379
Location: MS
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| Posted: Thu Jun 30, 2022 10:37 am Post subject: Thermocouple wire extension |
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On Wed, Jun 29, 2022 at 4:34 PM Paul Eckenroth <jeckenroth(at)nbn.net (jeckenroth(at)nbn.net)> wrote:
| Quote: | --> AeroElectric-List message posted by: "Paul Eckenroth" <jeckenroth(at)nbn.net (jeckenroth(at)nbn.net)>
As I redo my Revmaster engine with the burned stator I plan to incorporate thermocouples to hopefully allow me to head off a repeat of the burned stator. In the past on both the RV and the Onex I ran the full length of the suppllied thermocouple wire and then connected to tefzel coated copper for the rest of the run to the EIS using Faston connectors. The temperature read out for both planes seems reasonable and accurate. Although it has never been checked using boiling water. Now that I'm looking into thermocouples again I read that only thermocouple wire should be used for extensions and copper wire should never be used.
So, I am looking for some guidance. Is my prior approach totally faulty producing meaningless temperature readings or are the practices I read about only required for super accurate results and what I have done in the past good enough. I will appreciate any opinions. Thanks.
Paul
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IIRC, if you keep the transitions to copper at the same temperature as the final termination point (the gauge itself), and the copper extensions are identical with each other, it's supposed to have little effect on accuracy. IIRC (again) a lot of the issues with TC accuracy were driven by the old mechanical gauges that were actually driven by the thermocouple current. Modern electronic gauges are supposed to help alleviate some of the issues inherent in the old mechanical gauges.
No recent hotel stays, so you might want to verify the above through other sources.
Charlie
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Paul Eckenroth
Joined: 29 Jun 2010
Posts: 14
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| Posted: Mon Jul 04, 2022 1:36 pm Post subject: Re: Thermocouple wire extension |
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Thanks for the informative replies concerning the wire extensions. I was able to locate thermocouples with 6" leads so I don't think that wire extensions will be an issue.
Paul
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