The most commonly criteria used to make that choice are the temperature range, the chemical resistance, the abrasion and vibration resistance and the installation requirements. Installation requirements would also dictate your choice of a thermocouple probe.
Type K is the default first choice for everything above room temp. Type ``C'' (from Omega) for high temps to 2300 C. Use probes with ungrounded tips. Grounded only if you need fast response. Thermocouples are not suitable for sub-zero temperatures in most cases. Standard round pin connectors are best.
Commercial thermocouples range in size from 18-48 inches and are interchangeable. Universal thermocouples have millivolt rating of 25-35 mV. Type K, J and N thermocouples are commonly used with residential appliances, while other thermocouple types have industrial applications.
Your first steps to select the correct thermocouple for you is to choose the application where the thermocouple will be used, research the temperature ranges the thermocouple will be exposed to, consider any chemical resistance needed for the thermocouple or sheath material, assess the need for abrasion and vibration ...
It's easy to replace, and a new one costs $5 to $10. Rather than trying to unfasten the thermocouple inside the water heater's burning chamber, it's easier to remove the whole burner and thermocouple assembly.
There's really just one telltale sign of letting you know when the thermocouple isn't working, and that's when the pilot light won't stay lit. If you experience this problem, it's important to have your thermocouple assessed as soon as possible.
Type K Thermocouple (Nickel-Chromium / Nickel-Alumel): The type K is the most common type of thermocouple. It's inexpensive, accurate, reliable, and has a wide temperature range. Temperature Range: Thermocouple grade wire, –454 to 2,300F (–270 to 1260C)
Standard Thermocouples: Typically last 1-3 years in industrial applications. Specialized Thermocouples: Can last 5-10 years or longer in controlled environments.
Wire Size. The maximum temperature varies with the diameter of the wire used in the thermocouple. Although the type of thermocouple dictates the temperature range, the maximum range is also limited by the diameter of the thermocouple wire. That is, a very thin thermocouple may not reach the full temperature range.
Set the thermocouples 3/8 to 1/2" in from the ends of the tubes. Get them as close as you can. They don't have to be exactly perfect. Unplug or disconnect at the circuit breaker or disconnect switch.
An appropriate thermocouple connector must be attached to the proper T/C terminal for each type of thermocouple wire. The connector ground protects against electrical noise and the errors they may cause.
If your thermocouple goes bad, there is only one thing to do: Replace it. If you hire a professional plumber to do this, it may cost up to $200 for the labor.
If you try to relight a pilot light and the thermocouple is bent in a way that causes it to not make contact with the pilot light, the flame will instantly go out when you release the pilot control knob since the probe won't detect the heat from the flame.
Blow away Debris
Use short bursts of compressed air to blow dust and debris off the first 1⁄4 inch of the thermocouple's tip. Ensure no debris falls into the pilot assembly.
Know Your Thermocouple Type
In general, temperature range is the most important factor in choosing your thermocouple. From the frigidity of double-digit negative temperatures to the blistering heat measured in thousands, the range is your guide when choosing the perfect thermocouple.
You can easily identify a thermocouple type by the colors of its wire insulation. In this video we'll be focusing on the ANSI wire color coding used by the United States and Canada. In ANSI color coding, the red wire of a thermocouple is negative, and the positive wire is color coded to the type of thermocouple.
Type K has a wider temperature range than type J. Type K has better oxidation properties than Type J. Type J has higher sensitivity in the lower temperature range. Type J performs better in vacuum-like applications.
The most common types are J (black)-, K (yellow)- and T- (blue) type. The wire color indicates what type of thermocouple it is. (example: white + red wire insulations are used for J-type thermocouples; the colors of jacks and plugs for a J-type thermocouple is black.
Thermocouples are reliable temperature measurement devices used in many industrial applications, but even the most durable components can fail over time. So, why do thermocouples go bad? Various factors such as mechanical damage, overheating, and contamination can contribute to their deterioration.