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Thermowells and protection tubes

Normally sensor probes have to be protected against the process environment chemically as well as physically. Thermowells imply normally fully lathed cylindric or conical sheathings in metall. There are variants according to national German DIN-standards that still are referred to. The design should rather be directed by chemical, physical and measurement requirements. This is by the way Pentronic's speciality.

Protection tubes mainly mean steel tubes of the proper quality sealed with welded plug or washer at the measuring end. Ceramic protection tubes, a large special field, are normally necessary to protect thermocouples with noble metal wires, e g types R, S and B.


Mounting flanges are either fixed to the thermowell by welding or free to be positioned and then clamped to the wanted insertion depth. A special case is the so called tri-clamp coupling which is used in food and pharmaceutical industries.

Compression fittings

For probe diameters up to 6 - 8 mm Pentronic manufactures compression fittings, where a gland nut forces a cone to clamp the probe. The compression fitting can be threaded or welded to the wall which is subject to penetration. Several types of threads are available. There are three types of cones: steel, spring-action steel and PTFE. Spring-action steel kones are provided with a slot which at reasonable torque clamps the probe without making marks in it. Thus it will be possible to position the fitting along the probe. The PTFE-type can also be positioned. The compression fittings can be used on tubes as well as on metal sheathed probes.

Bayonet and adapters

Springloaded probes are often used in plastic industry to measure temperature on the bottom of drilled holes with good contact pressure. Pentronic manufactures springloaded sensors (thermocouples and Pt100s) with bayonet cap for fixed insertion lengths and contact pressure but also sensors with continuously adjustable insertion lengths and contact pressure. The bayonet caps and adapters are available in several sizes and forms.