Overview of Exhaust Gas Temperature (EGT) Sensor



1. Introduction

2. Operating principle

3. Position of the sensor

4. Thermocouple EGT sensor

    4.1 Features

    4.2 Circuit

5. Working process

6. Testing methods


1. Introduction


The exhaust gas temperature (EGT) sensor applies to the temperature regulation of the diesel particulate filter (DPF). It detects the exhaust gas temperature and converts it into a voltage. The message is for the electronic control system analysis. The sensor sets the temperature required for the DPF to reduce emissions and harmful gases to the atmosphere.


Purchase Exhaust Gas Temperature Sensor


The exhaust gas discharges from the combustion chamber. After passing through the high-speed rotating turbine, the gas rests in the cross-section outlet. The exhaust gas temperature is, in fact, the 'main indicator' of the engine's high-pressure rotor speed, swashplate position etc., so it must be very accurate.


2. Operating principle


The indicator shows the exhaust gas temperature due to the thermocouple induction, which means that it automatically generates an inductive electric potential signal when the engine exhaust gas temperature changes. 


The signal is then sent to the engine integrated regulator to alert the owner that the machine is over-temperature. The signal is also sent to the parameter indicator. Finally, the message is updated to the electronic system monitor processor, which provides the data of the engine exhaust temperature.


Nowadays, some experienced drivers use the EGT sensor in combination with the oxygen sensor to raise the temperature for more power.


3. Position of the sensor


Some high-pressure common-rail diesel vehicles equip the EGT sensor. It installs on the three-way catalytic converter or turbocharger of the vehicle's exhaust unit. The sensor detects the temperature of the exhaust gas inside the converter.




4. Thermocouple EGT sensor


Exhaust gas temperature sensors can be divided into thermistors, thermocouples and fuse three types. The thermocouple EGT sensor has a simple structure. It is easy to use. The thermocouple type usually consists of two different metal wires. It's not limited in size and with a protective sleeve, making it very easy to use.


4.1 Features


(1) High measurement accuracy


This sensor has high measurement accuracy. The thermocouple directly contacts the measured object. It's not affected by the intermediate medium.


(2) Wide measurement range


This sensor has a relatively wide measurement range. Common thermocouple measures from -50 ~ 1600 ℃ continuously. Some particular thermocouples can measure as low as -269 ℃, up to +2800 ℃.


The faulty exhaust gas temperature sensor does not accurately monitor the temperature, which arises a dangerous circumstance for the vehicle traveling.


4.2 Circuit


The thermocouple is one of the most common temperature detection components in the industry. The thermocouple works on the principle of the Seeback effect. Two conductors of different compositions connect at both ends to form a loop. If the two connected ends are at different temperatures, a thermal current generates in the loop.




These two different metal wires are welded together to form two junctions. The loop voltage VOUT is the difference between the junction voltage of the hot junction and the cold junction (reference junction). The VOUT is a function of the temperature difference. The proportionality factor α corresponds to the ratio of the voltage difference to the temperature difference. The α is called the Seebeck factor.


5. Working process


The exhaust gas temperature directly reflects the cylinder combustion condition. For diesel engines, the exhaust temperature leads to post combustion. At this time, the gas and oil circuit is likely to have problems.


Generally, this sensor doesn't install on vehicles. Most of today's temperature sensors are thermocouple type with slow response time. When a car runs on the road, its operating conditions are constantly changing, so the sensor doesn't reflect the current temperature in time.


But the EGT sensor used in the DPF is not the same as a normal one. It has a short response time, which approximates to reflect the real-time exhaust gas temperature.


When the engine is warm, monitor the exhaust gas temperature to provide a signal for the exhaust gas recirculation valve. A high engine temperature produces nitrogen oxides (NOx), allowing a certain amount of exhaust gas to enter the cylinder and then deteriorate the combustion environment. This process makes the combustion temperature lower. 


You should pay attention to the exhaust gas temperature in a cold engine, too. The oxygen sensor and three-way catalyst both need to rise to the right temperature to work correctly.




Therefore, during the engine warm-up period, the exhaust gas temperature needs to be increased as soon as possible to reduce exhaust gas emissions. The exhaust gas temperature is a parameter that allows for better control of exhaust gas emissions.


When the engine starts, the signal switch opens, and the ignition switch turns on simultaneously. At this moment, the alarm light goes off.


When the engine starts, the signal switch disconnects. The ignition switch is on. The alarm light is on and then off, which is the function set by the manufacturer to check if the warning light filament is fine.


During driving, when the exhaust gas temperature exceeds 900°C, the resistance value of the EGT sensor drops below 0.43kΩ, at which point the warning light is on.


When the platform floor temperature exceeds 125°C, the resistance of the floor temperature sensor exceeds 2kΩ, at which time the alarm light is on, and the buzzer makes noise.


When the exhaust gas temperature is below 900°C, and the vehicle floor temperature is also below 125°C, the resistance of the exhaust gas temperature sensor is more considerable than 0.43kΩ. The resistance of the floor temperature sensor is below 2kΩ. The alarm light isn't on, and the buzzer doesn't make noise.




6. Testing methods


(1) Visual inspection


When the ignition switch is on, the exhaust temperature indicator lights up. When the engine starts, the indicator goes off. These show that the sensor works normally.


(2) Check the component


Remove the exhaust gas temperature sensor. Heat the top 40mm long part until it is dark red near the flame. The resistance value between the sensor terminals should be between 0.4 and 20kΩ (for reference).


Interested in other sensors in the engine?


Visit http://www.delcoribo.com/contact to make an enquiry if you need more motor products.

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