How Does a Thermocouple Work?

Thermocouples happen to be the pairs of different metallic wires, which are connected at 1 of the ends, and that produce a net thermoelectric-voltage in the open pair as per the difference in the temperatures between those ends. The junction that has been brought into this very procedure, wherein the temperatures are measured, is known as the ‘HOT Junction. The second junction that is present at the end-point of the thermocouple’s material and that is always present near some gauges is known as the ‘COLD Junction.’

Seebeck Effect

In the year 1821, a physicist from Germany, whose name was Seebeck, discovered this thermoelectric effect, which happens to be the basis of today’s thermocouple technology. Seebeck had discovered that electric current flows into the closed circuits between 2 different metals when their 2 junctions happen to be at varying temperatures. The resulting thermoelectric-voltage that is generated will be depending upon the metals, which are being used, & the temperature relationship in these junctions. If both the 2 junctions have similar temperatures, then the voltage thus generated across each junction cancels each other out and there would be no movement of the current in the circuit. At different temperatures, different voltages develop at each junction & current will flow in this circuit. Therefore, the thermocouple can measure only the difference in temperatures between 2 junctions.

Cold Junction Compensation

A practical industrial/laboratory thermocouple has only one (measurement) junction; and the reference here is, at all times, the final temperature. The possible gauges or measures are as follows:- 

  • Accurately measures final temperature and compensates as per it while calculating the measured values. 
  • Locates the terminals in the thermally-controlled case. 
  • Don’t terminate in copper cable, instead use the compensating/actual thermocouple wire for extending the sensor termination to the connected instrumentation

Measuring Junctions

In general, 3 alternative tip-configurations are mostly offered, as mentioned underneath: 

  • Exposed (Measurement) Junction. This is advised for the temperature measurement of flow or static non-corrosive gas where the highest sensitivity & fastest response is needed. 
  • Insulated Junction: These are best suited for corrosive substances, though the thermal reaction is sluggish. In some of these applications where multiple thermocouples have been connected to relevant instrumentation, insulation might be needed in the measurement of circuits for preventing any false signals. If this has not been specified, then it is the default one. 
  • Earthed Junction: These are also suitable for corrosive & high-pressure applications. These provide a quicker response than insulated ones & also offer protection that exposed ones do not.

Hot Junction Formation Method

A proper hot junction method must be used to achieve good electrical contact in the wires of a thermocouple. For Chromal/Alumal as well as some other such combinations in high-temp applications, welding is the one & only way of obtaining a proper joint.

  • Tig welding: GTAW or Gas-tungsten-arc-welding, also called TIG or tungsten-inert-gas welding, is the sort of arc-welding, which makes use of a non-consumable tungsten electrode for producing the weld. The welding area tends to be safeguarded from atmospheric contamination by a shielding gas. 
  • Laser Beam Welding: LBW or Laser-Beam-Welding is a technique of welding, which is mainly made use of for joining more than one metal with a laser. This beam gives a concentrated heat source, which allows narrow & deep welds, and high-welding-rates. Laser-Beam-Welding happens to be a versatile way that can weld stainless steels, carbon steels, HSLA steels, aluminum & titanium. The welding speed is in the right ratio to the amount of input power, but it is also dependent upon the type & thickness of the processed pieces.

About Heatcon Sensors 

If you’re looking for a reliable and accurate heat sensor, look no further than Heatcon. We offer a wide range of heat sensors that are perfect for a variety of applications. Whether you need a sensor for research or industrial use, we have a sensor that will meet your needs.