Industrial Temperature Sensors

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Industrial Thermocouple Assemblies

Industrial thermocouple assemblies are used in the process and power industries where thermocouples are installed in pipe lines or vessels. This type of assembly consists of three basic parts, the connection head, sensing element and thermowell or protection tube. Selecting the proper assembly involves consideration of several factors including process temperature, environment, fluid or gas pressure, pipe or vessel size and flow velocity. The more commonly used configurations are listed on the following pages They represent only a small portion of Thermo Electric’s capability to manufacture quality products conforming to your specifications.

Thermo Electric products offer the following advantages:

  • Complete in-house manufacturing and control of raw material.
  • Weatherproof, explosion proof, corrosion proof connection heads.
  • High temperature Platinum Assemblies with ceramic wells.
  • Long length pipe wells.
  • Assemblies manufactured to major oil, power company, and contractor specifications.

Industrial Resistance Temperature Detector Assemblies

Resistance Temperature Detectors (RTD’s) operate under the principle that the electrical resistance of certain metals increases or decreases in a repeatable and predictable manner with a temperature change. RTD’s may have a lower temperature range than some thermocouples and a slower response time, however, they are more stable and repeatable over long periods of time. RTD’s higher signal output make them easier to interface with computers and data loggers and reduces the effects of radio frequency interference. Industrial RTD’s are used in the process and power industry, pipe lines and vessels. The more commonly used configurations are listed on the following pages They represent only a small portion of Thermo Electric’s capability to manufacture quality products conforming to your specifications.

The standard RTD employs either thin film or wire wound bulb depending on the temperature range desired. The most common is the platinum, 100 OHM with a temperature coefficient of resistance of 0.00385 ohms/ohm/°C. Standard tolerance is a grade B to ASTM E1137. For tighter accuracy the grade A is available.

Tube Skin Thermocouples

Tube skin thermocouples provide an efficient means of temperature measurement of tube walls in petrochemical plants and of boiler and super heater tubes in power plants. Made of metal sheath, MgO insulated thermocouple wire (CERAMO®) the runs can vary from just a few feet to over 50.

Tube skins are usually a grounded junction with a one inch square by 1/8″ thick weld pad factory curved to fit the contour of the process pipe. Pads may also be supplied wider and 1/16″ thick enabling the site to peen the pad to the pipe. Still others are equipped with a knife shape at the tip for faster response time. Knife edge tube skins can be provided in 1/2″ diameter, heavy wall sheath.

Shields may be added which curve around the pipe and over the junction and packed with a high temperature insulation to prevent heat from being transferred away from the junction thereby providing a more accurate temperature measurement.

Expansion loops or coils compensate for movement as the tubes are subject to thermal growth. Mounting clamps can be welded along the pipe for additional security.

Tube skins can be terminated in nipple extension with a compression fitting sealed inside the union to hold the sheath rigid then to a connection head. They can also be supplied to a same size transition as the sheath to allow for installation of a compression fitting attached to the housing wall then flexible lead wire for junction box termination. This design also allows the sheath to extend inside the junction box.

Thermo Electric will fabricate tube skin thermocouples to the requirements based on your installation drawings.

Multicouples

Very often there is a need to measure a temperature profile across a large tank or vessel. The method used is the multicouple which is an arrangement of thermocouple positions with measuring junctions at various depths. The intent is to monitor a number of temperatures at various points with all thermocouples or RTD’s contained in one assembly.

Multicouples are used in catalytic crackers, limekilns, distillation columns, pressurized reactor vessels and a host of other applications where such profiles are necessary. These type assemblies can be “miniaturized” where they are three feet long with two or three sensors, or they can be any length, even over one hundred feet long with twelve or more sensors.

Multicouples generally consist of a junction box suitable for terminating the thermocouples and joining them to cables running back to the measuring instrument, the thermocouples arrangement at various depths and a pipe protection well capable of withstanding the pressures and corrosives in the vessel.

Multicouples are custom made to locate measuring junctions at the key points in your process. Our years of experience and our qualified applications engineers can assist you in technical design of the proper multicouple.

Thermowells and Protection Tubes

Thermowells and protection tubes are generally attached into the process three ways, threaded, welded or a flanged connection. For smaller diameters where the well will not be required to be removed on a regular basis and corrosion is not a serious problem, threaded process connections are preferred. By threading into a coupling, thread-o-let or TEE the well is attached directly to the vessel or run pipe.

For installations where the well needs to be removed more frequently due to corrosion or other requirements, a flange connection is used. The flange connection will bolt to a mating flange mounted to the process. Flange connections are more appropriate for high pressure applications and larger pipe sizes.

For applications where access is not required a weld-in or socket well can be used. These provide a high quality connection, but obviously cannot be removed without significant effort. Welded connections are also preferred for high pressure, high temperature steam lines.

Protection tubes or pipe wells are generally less expensive than drilled bar stock styles and are used in applications where pressure and velocity are low enough that the stronger drilled bar stock types aren’t required or where long lengths are needed. A typical application is in stack gas temperature monitoring where a high temperature alloy is used as pipe material. Protection tubes can be welded directly into a vessel or supplied with a threaded bushing or flange welded in place for threaded or flanged process connection.