One of the great benefits of a community of heat treaters is 
the opportunity to challenge old habits and look at new ways of doing things. Heat Treat Today’s 101 Heat Treat Tips is another opportunity to learn the tips, tricks, and hacks shared by some of the industry’s foremost experts.
For Heat Treat Today’s latest round of 101 Heat Treat Tips, click here for the digital edition of the 2019 Heat Treat Today fall issue (also featuring the popular 40 Under 40).
Today’s tips come to us from Pelican Wire, covering Thermocouples. This includes advice about correcting irregular part distortion and finding solutions to cracked parts.
If you have a heat treat-related tip that would benefit your industry colleagues, you can submit your tip(s) to anastasia@heattreattoday.com or editor@heattreattoday.com.
Heat Treat Tip #65
Introducing Your Common Thermocouple Types
What are the common thermocouple types?
Thermocouple material is available in types K, J, E, N, T, R, S, and B. These thermocouple types can be separated into two categories: Base and Noble Metals.
Types K, J, E, N, and T are Base Metals. They are made from common materials such as Nickel, Copper, Iron, Chromium, and Aluminum. Each base metal thermocouple has preferred usage conditions.
Types S, R, and B thermocouples are Noble Metals because they are made of one or more of the noble metals, such as Ruthenium, Rhodium, Palladium, Silver, Osmium, Iridium, Platinum, and Gold. Noble metals resist oxidation and corrosion in moist air. Noble metals are not easily attacked by acids. Some Noble metal thermocouples can be used as high as 3100°F.
Heat Treat Tip #66
Culprits of a Stable Thermocouple
Factors affecting the stability of a thermocouple:
The EMF output of any thermocouple will change slightly with time in service and at elevated temperatures. The rate and change are influenced by metallurgical and environmental factors. The four factors that can induce EMF drift are: Evaporation, Diffusion, Oxidation, and Contamination.
Heat Treat Tip #67
Does Length Matter?
Does the length of a thermocouple wire matter?
In a word, “Yes.” There are several factors when considering the maximum length of a thermocouple assembly. Total loop resistance and electrical noise. Total loop resistance should be kept under 100 ohms for any given thermocouple assembly. Remember, the total loop resistance would include any extension wire used to complete the circuit. Motors and power wires can create noise that could affect the EMF output.
Heat Treat Tip #69
Thermocouples Pros & Cons
Pros of thermocouples
1. high accuracy,
2. adaptable to harsh environments as well as high vibration,
3. fast thermal reaction,
4. wide operating temperature range,
5. good reproducibility,
6. low cost.
Cons of thermocouples?
1. Stray voltage pick is possible;
2. The cold junction and lead compensation are essential;
3. They are nonlinear;
4. They have a low output voltage, i.e., less sensitivity.
Heat Treat Tip #70
Type N Thermocouple (Nicrosil/Nisil)
Type N Thermocouple (Nicrosil/Nisil): The Type N shares the same accuracy and temperature limits as the Type K. Type N is slightly more expensive and has better repeatability between 572°F to 932°F (300°C to 500°C) compared to type K.
