Guide to Use a Thermocouple
Here’s a quick guide to use a thermocouple. First and foremost, it is important to know what a thermocouple is and for what application you need it! By knowing the application, you can start using the thermocouple in the correct way.
About Thermocouple Sensors
Thermocouple sensors are the tools utilised for measuring temperatures; they use 2 different types of metal wires. These are connected at 1 of the ends & are connected to the thermocouple’s thermometer at the other. The thermocouple sensor along with the thermometer allows us to send signals to each other; and, if configured correctly, can provide accurate temperature measurement(s). The temperature range is quite wide and can reach up to 1250 degree Celsius. This surely depends on what sort of thermocouple being used, some do not even reach that particular range & some could also detect boiling temperatures below -200 degree Celsius. Thermocouple sensors are useful in instant temperature detection. They’re even known for versatility as they’re quite commonly used in many applications. They’re even available in various types of models. It’s also quite significant to understand that each model type has its own basic structure and how the devices work. You need to choose the right type of thermocouple sensor that is most suitable for your application.
Types of Thermocouples
- Beaded Wire Thermocouple: This happens to be one of the simplest forms of thermocouples. This has 2 thermocouple wires that are connected through a welded bead. That’s the reason why it’s called a wire-thermocouple. Though the thermocouple’s welded bead tends to be exposed, still it’s limited to only a few applications. Do not use this beaded thermocouple in a liquid environment or immerse it in liquid, as it can corrode/oxidize the thermocouple’s compound. Making use of metal surfaces can sometimes be difficult. Often, metal surfaces used in ground power systems have a non-direct connection with the power system, which can affect thermocouple’s measurements. In other words, such thermocouples are ideal for gas temperature measurement. The reason being their smaller size and faster response time.
- Thermocouple Sensor: These work by placing a thermocouple wire inside a metal tube. This tube is known as the sheath. The probe sheath is constructed out of standard stainless steel & Inconel®, which supports higher temperatures than stainless steel. However, stainless steel is generally preferred over Inconel due to its broader chemical compatibility. If very high temperatures are involved, other exotic shell materials are even available. The only thing different is the tip of the thermocouple probe.
- Surface Probe: The most difficult part of thermocouples is the measurement of a solid surface. Most temperature sensors cannot perform this task. So, to get an accurate measurement, the entire measuring area must be connected to the surface. Rigid sensors & rigid surfaces are difficult to work with. Such types of thermocouples are ideal for surface measurement because they can even be built into a rotary mechanism.
How Does It Work?
When 2 conductors are made of different metals, with 1 of the ends connected, & when heated, a constant current flows in the thermoelectric circuit. Now, if the said circuit somehow gets broken towards the middle of it, then the open-circuit-voltage (which is the Seebeck-voltage) happens to be a function of the junction’s temperature & lies among the 2 metal compounds. So, this means that when the junction of two metals is heated or cooled, a voltage is created that can be inversely correlated with temperature. The measurement works like this.
Other Categorizations of Thermocouples
There are several characteristics as well as different varieties of thermocouples, each of these types tend to have different characteristics. They are also having different combinations of metals and/or calibration(s). The most common are “base-metal-thermocouples.” The most common types are N, T, E, E J & K. In addition, there’re also high temperature calibrations, also known as “Noble-Metal-Thermocouples,” which happen to be types R, S, C and GB. Various sorts of thermocouples have distinct calibration ranges as well as varied metal combinations/alloys. Each of these fittings tend to have different temperatures as well as environment. The max temperature can vary depending on the wire diameter used in the thermocouple. Even though the calibration tends to determine the temperature-range, the max-temp range is limited as well. This is due to the diameter of the thermocouple wire. The finer the thermocouple wire, the lower the chance of reaching the entire temperature evenly. A K-type thermocouple is known as a general-thermocouple.
Selecting the Right Thermocouple
There are 3 different styles in toto, which are ungrounded, grounded, & exposed.
- The grounded end of the thermocouple contacts the enclosure wall, which when in place, provides a faster response time, and is most sensitive to electrical ground loops.
- For an ungrounded connection, the thermocouples are separated from the sheath’s walls by insulating layers.
- The thermocouple’s end extends outside the enclosure wall with an open junction. These open junction thermocouples are best suited for measuring air.
Buy Thermocouples from Heatcon Sensors
Choose the right thermocouple by understanding the guide to use a thermocouple provided above; else call Heatcon for making the right choice in this regard!