What are the installation precautions for type R and type J thermocouples

There are big differences between type R and type J thermocouples in terms of the materials they are made of, the range of temperatures they can monitor, and the environments they can work in. Because of this, the measures that need to be taken when installing them are also different. Type R thermocouples are made of high-precision noble metals, so they need to be installed with care to keep the environment clean, avoid interference, and stay stable over time. kind J thermocouples are a general-purpose kind made of base metal. They focus on protecting against oxidation, avoiding corrosive situations, and making sure there is good contact.




I. Common Installation Principles: These work for both type R and type J thermocouples.



The following precautions are necessary for both types of thermocouples and are necessary for getting the right temperature reading:



Choose a representative temperature measuring point: The installation site should be far away from the edge of the heat source, the furnace door, or places where the temperature changes a lot to make sure that the measured temperature accurately reflects the overall state of the measured medium.



Make sure there is enough contact and depth of insertion:



The working end of the thermocouple must touch the measured medium all the way around. It is best if the insertion depth is more than 10 times the outside diameter of the protective tube, but it should be at least 8 to 10 times.



When putting it in a pipeline, the end of the protective tube should stick out 5–10 mm past the centerline of the pipeline. This will put it in the area of maximum flow velocity, which will speed up the response time.



Avoid losing heat and making mistakes with radiation.



If the temperature of the pipe wall is much higher or lower than typical when monitoring gas temperature, the thermocouple may cause the measurement to be off because of heat radiation. A shielded structure, like a shielded thermocouple, can help lessen this effect.



To keep heat from escaping, exposed areas should be well insulated.



Using Compensating Leads the Right Way



You need to choose compensating leads that match the thermocouple's calibration, and the polarity connection must be proper to avoid adding extra potential.



The temperature around the compensatory lead joint should not be more than 100°C. If it is, you need to take steps to keep the heat in.



Ways to stop electromagnetic interference



You should keep signal cables away from places where there are high electric and magnetic fields. To avoid signal distortion, it is best to use shielded wires and make sure they are properly grounded.



Sealing and fixing with tools



When there is negative pressure or dangerous gases, the installation interface must be tightly sealed so that outside air can't get in and mess up the measurements.



Installation should be safe so that vibration or impact doesn't move or break anything. If needed, put in support brackets.







II. Special installation safety measures for Type R thermocouples (high-temperature, precious metal type for precise measurement)



Type R thermocouples (platinum-rhodium 13-platinum) can accurately monitor temperatures below 1300°C. When installing, keep the following in mind:



Stay away from "platinum brittleness" and contamination.



Type R thermocouples are very sensitive to dirt and other things that shouldn't be there. During installation, stay away from oil, dust, metal vapors, and reducing gases like H₂ and CO. If you don't, "platinum brittleness" may happen, which can cause wires to break.



Recommended for Use in Atmospheres That Are Oxidizing or Inert Long-term use in places where there are sulfur or carbon deposits is not allowed.



Suggested Use of High-Purity Protective Tubes



It is best to use protective tubes made of 99% high-purity alumina (corundum) or silicon carbide to make the service life longer and keep the tubes from getting dirty.



To keep air from moving through the gap between the protective tube and the furnace wall, it should be tightly sealed with refractory material. This will keep the temperature measurement from being affected.



Control of the temperature at the cold junction and the position of the junction box



Do not put the junction box right up against the wall of the furnace that gets hot. To keep the signal stable, the cold junction should be at least 200 mm away from the furnace wall.



To keep rain, dust, or condensation from getting in, the cover of the junction box should be facing up or the cable outlet should be facing down.



Recommendation for Vertical Installation



To keep the protective tube from bending under its own weight at high temperatures, the installation should be as vertical as feasible. If you have to put it horizontally, the depth of the hole shouldn't be more than 500mm, and a heat-resistant bracket should be added for stability.







III. Special installation tips for Type J thermocouples (base metal type, medium and low temperature industrial uses)



Type J thermocouples (iron-constantan) are used a lot in factories and other places where the temperature ranges from -210°C to 750°C. During installation, it is important to pay close attention to preventing corrosion and oxidation:



Use Less in Places Where Oxidation Happens at High Temperatures



Above 500°C, the iron cathode's oxidation rate goes up very quickly. For long-term use, it is best to keep the temperature below 500°C.



If you need to utilize it at high temperatures, you should put a protective sheath over it (such stainless steel or ceramic tubing) and not install it in the open.



Not Allowed to Be Used in Places with Sulfur



Constantian negative electrodes are very sensitive to sulfides. They will quickly corrode and break when they come into touch with gases that include sulfur, including SO₂. This can cause thermoelectric potential drift or even open circuits.



Type K or type E should be used in places like oil refining, coking, and other places where sulfides might be present.



Keep Rust and Moisture Away



Type J electrodes work better in humid settings, however iron electrodes can rust, and being in high humidity for a long time can make them less stable.



To keep moisture from getting in, you should check the sealing of the terminals and protective tubes on a regular basis.



Bigger wire diameter means a longer life



For use in high temperatures or hard situations, a variant with a bigger wire diameter is recommended. This can make the service life last more than 40% longer.



After installation, let it cool down naturally. Don't let it cool down too quickly.



Don't use water or strong winds to cool things down quickly after using them at high temperatures. This could harm the insulating layer or the connection wires.