Choosing a Thermocouple for Rubber-Lined Tubes

Hi everyone,
I’m working on a setup where I need to measure the temperature inside the rubber lining of a steel tube, in addition to using a flow meter. Here are some details:
Steel tube wall thickness: 3/8” (~9.5mm)
Rubber lining thickness: ~3/4” (~19mm)
Desired sensor insertion: About 1/4” to 3/8” (~6–10mm) into the rubber
Preferred sensor type: Thermocouple, Type J or K
Temperature range: 20–150°C
Lead length: 20 ft (~6 meters), with ~6–12” of the wire protected by heat shrink near the junction
Previously used: A sensor as shown in the attached image (threaded into the metal tube)
I'm wondering if simple thermocouple cables taped to the outside would be sufficient, or does anyone recommend something sturdier? Thanks!

Isolde wrote:Hi Isolde,
Thanks for the details! If the pipe is rubber-lined, we recommend using a flanged sensor instead of a threaded one for better reliability. However, we understand that you may be working with a metallic tube housing, so threading could still be an option if done correctly.
To clarify:
1. Do you confirm that you accept flange connection if required?
2. What’s the exact probe diameter you prefer—5mm or 6mm?
3. Can you confirm the precise insertion depth, including both tube and rubber?
4. The lead wire is 6 meters and only needs heat shrink at the joint—correct?
Let us know and we’ll propose a model that meets your needs.

ATO wrote:Thanks for the response. Here’s more clarification:
1. The tube is made of metal, and the threading is fine. That’s how we’ve installed thermocouples previously (see image).

2. Probe diameter: 4.5 to 5mm
3. Insertion depth: The Steel tube is ~8mm thick. We'd like an additional 6–20mm into the rubber lining, so ideally total insertion of 14–28mm. Something adjustable would be great, but fixed is okay too—~20mm total is preferred.
4. Yes, the lead is 6 meters, and heat shrink is only needed at joints to avoid damage from twisting or handling.

Isolde wrote:Isolde, based on your details, we recommend:
Model: J-type thermocouple ATO-TC-JS
Probe diameter: 5mm
Insertion depth: ~20mm
Connection: 1/2NPT threaded
Lead wire: 6m with heat shrink at junctions
Temp range: 20–150°C

ATO wrote:ok! Thanks for the recommendation!