### Mobile Generator and Power Console Trailers by Hotfoil-EHS

Hofoil-EHS manufactures mobile generator trailers for welding heat treating power and temperature control. Custom designed from large to small, Hotfoil-EHS will build to your specification.

609-588-0900

### Dissimilar Metal Junctions (How Thermocouples Work)

When two dissimilar metal wires are joined together at one end, a voltage is produced at the other end that is approximately proportional to temperature. That is to say, the junction of two different metals behaves like a temperature-sensitive battery. This form of electrical temperature sensor is called a thermocouple:

This phenomenon provides us with a simple way to electrically infer temperature: simply measure the voltage produced by the junction, and you can tell the temperature of that junction. And it would be that simple, if it were not for an unavoidable consequence of electric circuits: when we connect any kind of electrical instrument to the thermocouple wires, we inevitably produce another junction of dissimilar metals. The following schematic shows this fact, where the iron-copper junction J1 is necessarily complemented by a second iron-copper junction J2 of opposing polarity:

Junction J1 is a junction of iron and copper – two dissimilar metals – which will generate a voltage related to temperature. Note that junction J2, which is necessary for the simple fact that we must somehow connect our copper-wired voltmeter to the iron wire, is also a dissimilar-metal junction which will also generate a voltage related to temperature. Further note how the polarity of junction J2 stands opposed to the polarity of junction J1 (iron = positive ; copper = negative). A third junction (J3) also exists between wires, but it is of no consequence because it is a junction of two identical metals which does not generate a temperature-dependent voltage at all.

The presence of this second voltage-generating junction (J2) helps explain why the voltmeter registers 0 volts when the entire system is at room temperature: any voltage generated by the iron-copper junctions will be equal in magnitude and opposite in polarity, resulting in a net (series-total) voltage of zero. Only when the two junctions J1 and J2 are at different temperatures will the voltmeter register any voltage at all.

Reprinted from "Lessons In Industrial Instrumentation" by Tony R. Kuphaldt – under the terms and conditions of the Creative Commons Attribution 4.0 International Public License.

### Hotfoil-EHS Heat Treating Power Consoles

Precise control over your pre-weld and post-weld heat treatment parameters are critical. Accurate temperature control, specific soak times, uniformity, and controlled heat up and cool down times are required to ensure strong welds. Hotfoil-EHS power consoles are designed to provide the best control, easiest user interface, and longest lasting operation, even in the toughest environments. Using only the highest quality components, Hotfoil-EHS power consoles are field-tested and application proven. Control systems can be specified with or without recorders or ramping controllers, and are standardly available in 6, 9, 12, 18, and 24 zone configurations.

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

### The ICE Advanced Heat Treatment Control System

The ICE IS System, is developed for precise, reliable and efficient heat treatment control. It consists of IS controllers and ISPort software. With ISPort software you can define process parameters as temperatures, rates, tolerances etc; operate and control one or many processes from one or several controllers; edit PID values; fill in needed information, ex. customer info, work info etc.; print all work documents and heat treatment certificates. For more information contact Hotfoil-EHS,

https://hotfoilehs.com/icestar
609-588-0900

### 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.

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

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

• High output
• Fast
• Two-wire ohms measurement