Common Temperature Sensors Used in Industry

THERMOCOUPLE
Due to their simplicity, reliability, and relatively low cost, thermocouples are widely used. They are self-powered, eliminating the need for a separate power supply to the sensor. Thermocouples are fairly durable when they are appropriately chosen for a given application. Thermocouples also can be used in high-temperature applications.

Thermocouple Advantages:

• Self-powered
• Simple
• Rugged
• Inexpensive
• Many applications
• Wide temperature range
• Fast response

Thermocouple Disadvantages:

• Nonlinear output signal
• Low voltage
• Reference required
• Accuracy is function of two separate measurements
• Least sensitive
• Sensor cannot be recalibrated
• Least stable

RTD
Resistance temperature detectors are attractive alternatives to thermocouples when high accuracy, stability, and linearity (i.e., how closely the calibration curve resembles a straight line) of output are desired. The superior linearity of relative resistance response to temperature allows simpler signal processing devices to be used with RTD’s than with thermocouples. Resistance Temperature Detector’s can withstand temperatures up to approximately 800 C (~1500 F).

RTD Advantages:

• More stable at moderate temperatures
• High levels of accuracy
• Relatively linear output signal

RTD Disadvantages:

• Expensive
• Self-heating
• Lower temperature range

THERMISTOR
Thermistors work similarly to RTD’s in that they are a resistance measuring device, but instead of using pure metal, thermistors use a very inexpensive polymer or ceramic material as the element.

Thermistor Advantages:

• High output
• Fast
• Two-wire ohms measurement

Thermistor Disadvantages:

• Nonlinear
• Limited temperature range
• Fragile
• Current source required
• Self-heating

Industrial Heat Treatment Furnaces, Big and Small

Here at Hotfoil-EHS, we are capable of building furnaces of many sizes, big and small. From small, low-throughput furnaces, to much larger high yield furnaces, to rail-driven furnaces designed to move back and forth over the materials being heated, Hotfoil-EHS Design Engineers and Fabrication Shop has done it all. Gas or electric, Hotfoil-EHS has the experience to build a custom furnace to your exact specification.  If you can think it, we can build it!

Hotfoil-EHS
https://hotfoilehs.com
609-588-0900

Indirect Resistance Heating

Indirect resistance heating example:
Weld preheat ceramic mat heater.

With indirect resistance heating, a heating element transfers heat to the material by radiation, convection, or conduction. The element is made of a high- resistance material such as graphite, silicon carbide, or nickel chrome. Heating is usually done in a furnace, with a lining and interior that varies depending on the target material. Typical furnace linings are ceramic, brick, and fiber batting, while furnace interiors can be air, inert gas, or a vacuum.

Indirect resistance heating can also be done with an encased heater, in which the resistive element is encased in an insulator. Called metal sheath heaters this type of heater can be placed directly in liquid to be heated or close to a solid that requires heating. Numerous other types of resistance heating equipment are used throughout industry, including strip heaters, cartridge heaters, and tubular heaters.

Indirect resistance heating example: 
Clamp-on pre-weld electric heater.

Resistance heaters that rely on convection as the primary heat transfer method are primarily used for temperatures below 1,250 ̊F. Those that employ radiation are used for higher temperatures, sometimes in vacuum furnaces.

Indirect resistance furnaces are made in a variety of materials and configurations. Some are small enough to fit on a counter top, and others are as large as a freight car. This method of heating can be used in a wide range of applications. Resistance heating applications are precisely controlled, easily automated, and have low maintenance. Because resistance heating is used for so many different types of applications, there are a wide variety of fuel-based process heating systems, as well as steam-based systems, that perform the same operations. In many cases, resistance heating is chosen because of its simplicity and efficiency.

Indirect resistance heating example: 
Electric hopper heaters.

Indirect resistance heaters are used for a variety of applications, including heating water, sintering ceramics, heat pressing fabrics, brazing and preheating metal for forging, stress relieving, and sintering. This method is also used to heat liquids, including water, paraffin, acids, and caustic solutions. Applications in the food industry are also common, including keeping oils, fats, and other food products at the proper temperature. Heating is
typically done with immersion heaters, circulation heaters, or band heaters. In the glassmaking industry, indirect resistance provides a means of temperature control. Many hybrid applications also exist, including “boosting” in fuel-fired furnaces to increase production capacity.

Resistance heating applications are precisely controlled, easily automated, and have low maintenance. Because resistance heating is used for so many different types of applications, there are a wide variety of fuel-based process heating systems, as well as steam-based systems, that perform the same operations. In many cases, resistance heating is chosen because of its simplicity and efficiency.

Contact Hotfoil-EHS for any industrial resistance heating project. With decades of application experience, Hotfoil-EHS engineers can help you design a system tailored to your exact needs.