What is an EGT Probe Thermocouple?

What is an EGT Probe? How Does it Work? We are asked these questions by our customers just about every day. Exhaust Gas temperature probes are an important tool for monitoring engine temperatures. But there is a lot more going on below the surface than meets the eye. We made this video to help educate and inform our customers about the technology. We hope you enjoy it! Our EGT probes are Made in the USA and engineered for performance. Talk with the experts - The Sensor Connection.

EGT Probe Basics – EGT Probe Tutorial

Exhaust Gas Temperature (EGT) Probes are sensors that measure and convert the temperature of exhaust gas into a corresponding electrical signal. This electrical signal is then measured and displayed as a readable temperature by a monitoring instrument such as an EGT gauge.

Measuring Technologies

The 3 most common measurement technologies used in EGT probes are Thermocouple, RTD, and Thermistor.  This video will focus on Thermocouple EGT probes, since they are the most widely used.

How Does an EGT Probe Thermocouple work?

An EGT Probe Thermocouple consists of two conductors made from dissimilar metals, welded together at one end to form a junction.  When the junction is heated or cooled, an emf voltage is created.  A thermocouple gauge, amplifier, or other electronic instrument measures the EMF voltage and will display the correct temperature of the junction.

The Anatomy of a Sensor Connection EGT Probe Thermocouple

Sensor Connection EGT probe thermocouples have the following components. 

The Stem.  The outer sheath of the stem is a tube made from a metal such as stainless steel or Inconel.  Inside the sheath tube are two thin thermocouple conductors that are supported & protected by a compacted powder made from the mineral magnesium oxide. 

At the tip of the Stem the two thermocouple conductors are welded together to form the measuring junction, this junction may be exposed or enclosed. 

Since exposed junctions come in direct contact with the exhaust gas, they have the fastest response time but have a shorter service life. 

Enclosed ungrounded junctions do not come in direct contact with the exhaust gas and as a result will have a slower response time, but as a benefit, a longer service life.

An EGT probe with a 90 degree bend has both a hot & cold leg length.  These leg lengths can be customized to fit a customer’s specific application.

At the base of the Stem is a transition fitting.  This is the point which the Stem’s conductors end and are welded to the start of the Signal Cable wires.  A high service temperature Epoxy is then injected into the transition fitting to support the wires and protect against the entry of liquids.

Next, a strain relief spring is threaded onto the transition fitting.   The strain relief prevents sharp bending of the signal cable to ensure reliability and longevity at this critical attachment point.   

The signal cable wires are stranded and made from the same thermocouple metals as the stem conductors.  The two signal wires have a layer of Teflon for insulation and an additional water proof Teflon outer jacket, followed by a stainless-steel braiding to protect the cable from nicks, cuts, and abrasions.

These components come together to create an exhaust gas temperature probe that is precise, dependable, and customized to satisfy your demanding application. 

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