1. Know if it is made with Mineral Insulated Cable.
There are two main ways EGTs can be constructed. One way uses Mineral Insulated (MI) Cable. The other way uses thermocouple wire inside of a Stainless-Steel Tube. Quality EGTs will always be made using MI Cable. MI Cable uses Magnesium Oxide (MgO) Powder to insulate the conductors. This ensures long-lasting durable EGTs that can see high temperatures inside aggressive environments. In contrast, the wire and tube designs are flimsy and can quickly cause problems for your readings. These problems include false readings, slow readings, and ultimately open readings. All Blaze Probes EGTs are made using MI cable. A quick way to determine if your EGT has MI cable is whether or not the EGT has a fitting and spring. If it does, this means a transition from wire to MI cable has been made.
2. Know the purity of the Mineral Insulated Cable.
The purity of the conductors, as well as the Magnesium Oxide (MgO) inside the Mineral Insulated Cable, is of the utmost importance for a fast-accurate reading. Without these standards, EGTs can see 20, 50, or even a 100+ degree difference in accuracy depending on the operating temperature. Some cheaper manufacturers of MI Cable (outside of North America) will use MgO with very low purity on one or both of the conductor metals. These impurities will cause huge inaccuracies and/or cause the temperature to plateau. If you suspect inaccuracies with your EGTs, ask the manufacturer for their MI Cable Certification and the Raw Material Report. Blaze Probes uses MI Cable that is Certified for Special limits of error under ASTM Accuracy standards.
The Outer Sheathing for your high-temperature EGTs should be Inconel 600. This is to shield against not only those high temperatures but caustic and harsh environments as well. This is the ideal construction over the standard Stainless-Steel variations depending on your application.
3. Know which junction type is best for your application.
There are three main junction types which are Grounded, Ungrounded, and Exposed. You will want to know the function of each one to determine which will be best for your specific application. This can save you a lot of time and money when choosing the best thermocouple or more specifically EGT.
4. Know how to spot a bad Exposed Junction.
As the preferred junction type, it is important to take a closer look at the exposed junction as well as go over the criteria for what makes or breaks its quality. There are two primary criteria when looking at the exposed junction option: The junction weld and the MgO powder.
Take a look at the weld on the junction. The conductors need a certain amount of clearance from the MgO powder to allow airflow. The conductors also need to be pressed slightly together with a consistent and clean weld bridging the two. Watch out for pits or gaps on the edges. If these imperfections are large enough, it will not be good for the longevity of the EGT.
The MgO powder for exposed junctions goes through a hardening process. This solidifies the powder so that it can withstand extreme heat and vibration without causing any of the powder to fall out. This process makes the EGT rugged and able to last run after run while maintaining speed and accuracy. To spot a bad seal, simply take a knife and scrape at the white powder. If the powder falls out, then you know what is going to happen in your exhaust system.
5. How to spot a bad bend.
This is the last EGT quality spot check and is also the easiest to identify. If you have a bend on your EGT, you want the conductors inside the MgO to be parallel with the bend. You do not want your conductors to overlap. This can cause the conductors to pinch together at the bend point and touch, causing a false junction and an inaccurate read point. To see this visually, you can simply look at the orientation of the conductors on an exposed junction. Make sure the conductors come out oriented parallel with the bend. If it is a grounded or ungrounded junction, you can look at the orientation of the wire leads.
Use these checks next time when buying EGTs to ensure a quality, durable, fast, and accurate Exhaust Gas Temperature Probe.