FAQ about Sheaths and Covers for Industrial Temperature Sensors

In this section, we answer the most frequently asked questions about protective sheaths and covers for thermocouples and PT100 probes, including their function, materials, applications, and selection criteria for demanding industrial processes. The content is geared towards engineers, maintenance personnel, and process managers who require reliable temperature measurement solutions.

What is a protective sheath for temperature sensors?

A protective sheath is a rigid element that protects the temperature sensor (thermocouple or PT100) from direct contact with the process. Its function is to isolate the sensor from high temperatures, pressure, corrosion, abrasion, or aggressive atmospheres, increasing its lifespan and facilitating maintenance.

What is the difference between a sheath and a case?

In the industrial environment:

Sheath: rigid, metallic or ceramic protection, designed to withstand severe conditions.
Case: term used for specific protections, usually consumables or for specific measurements, such as silicone cases.

Both elements serve the function of protecting the sensor, but with different levels of robustness and durability.

What is the purpose of a sheath on a thermocouple or PT100?

The sheath allows:

Protect the sensor from high temperatures
Prevent damage from corrosion, oxidation or abrasion
Isolate the pressure or velocity sensor from the fluid
Replace the sensor without disassembling the installation

It is a key component in critical industrial processes.

What materials are used in protective sheaths?

The sheaths are manufactured according to the process, temperature, and working atmosphere. The most commonly used materials are:

AISI 304 stainless steel
AISI 316 stainless steel
AISI 310 stainless steel
AISI 446 stainless steel
Inconel 600 / 601
253MA
Technical ceramics (C610, C710 and C799)

The correct selection of material directly influences the durability, reliability, and safety of the measurement system.

When is it recommended to use a ceramic sheath?

Ceramic sheaths are primarily recommended for:

High-temperature processes
Industrial ovens
Highly oxidizing atmospheres

They offer excellent thermal resistance, although less mechanical resistance than metal sheaths.

What types of ceramics are used in ceramic pods?

Ceramic sheaths are manufactured with different qualities of alumina, depending on the thermal and mechanical requirements of the process:

Ceramic C510
Ceramic C610
Ceramic C710
Ceramic C799

Higher alumina purity results in greater temperature resistance and better performance in demanding thermal processes.

What are the applications of sheaths made from AISI 446 steel?

AISI 446 stainless steel sheaths are used in high-temperature applications where high oxidation resistance is required.

Jemar Termometría manufactures custom-made AISI 446 sheaths, a common solution in industrial furnaces and continuous thermal processes where other stainless steels do not offer adequate performance.

How do you choose a suitable sheath for an industrial process?

To select a pod correctly, the following should be considered:

Maximum and continuous temperature
Type of atmosphere (oxidizing, reducing, corrosive)
Pressure and speed of the process
Required immersion length
Sensor type (thermocouple or PT100)

An incorrect selection can cause premature sensor failure.

Do the pods affect the sensor's response time?

Yes. The sheath acts as a thermal barrier:

Greater thickness → greater protection, slower response
Thinner → faster response, less protection

The design must balance protection and response speed.

Can custom-made sheaths and cases be manufactured?

Yes. Jemar Termometría manufactures custom-made sheaths, adapting the material, diameter, length, and fixing system to the actual conditions of the industrial process.

What are silicone cases and what are they used for?

Silicon sheaths are used as thermocouple protection in molten metal temperature measurement, especially in steelmaking and foundry work.

These sleeves are designed for spot or short-duration measurements under extreme conditions. Jemar Termometría acts as a distributor for the silicon sleeve manufacturer, supplying them in various lengths and diameters depending on the application.

What types of fastening systems can the sheaths have?

The pods can be supplied with:

Thread (BSP, NPT, metric)
Flange
Sliding fitting
Direct welding

The fixing system is defined according to the installation and the process.

Can the sensor be replaced without removing the sheath?

Yes. One of the main advantages of the pods is that they allow the sensor to be removed and replaced without disassembling the pod or interfering with the process, reducing downtime.

In what industrial applications are sheaths and covers used?

Sheaths and cases are used in:

Industrial ovens
Iron and steel industry and metallurgy
Chemical industry
Energy
Continuous thermal processes
Autoclaves and reactors

They are essential when the sensor operates under severe industrial conditions.