New, more robust RTD temperature sensor

New sensor from Danfoss combines thin film technology and thermocouples

To prolong the life of marine diesel and gas engines, it’s important to monitor and control exhaust gas temperatures – and this requires an accurate temperature sensor. Based on two types of sensor technology, temperature sensors either use a Resistance Temperature Detector (RTD) with PT100 thin film technology, or thermocouples. Both technologies have their pros and cons and in Asia, RTDs are the sensor of choice, while in Europe thermocouples are popular. But this practice is about to change, thanks to a new sensor from Danfoss that combines the best from both technologies. Small diameter, two RTD elements No matter what technology you use to measure exhaust gas temperatures, there are advantages and disadvantages. Thermocouples are ideal for high temperatures up to 800°C. They are also small in diameter, and they’re very stable mechanically. The disadvantages are that they’re subject to electronic noise, have a weak mV signal, and need a special compensation cable.

Photo by Danfoss A/S

The RTD sensors, on the other hand, have a strong Ohm signal, are not susceptible to electronic noise, and don’t need special cables. On the downside, they’re not as strong mechanically, can only cope with temperatures up to 600°C, need larger sensors, and use three wire cables to operate over long distances. But this is about to change..

Danfoss was aware of a growing interest in exploiting the advantages of RTD technology in Europe. So Danfoss worked with a major engine manufacturer to develop a 2xPT1000 sensor that has all the advantages of RTD, without the drawbacks.

One of the key challenges was finding a way to fit two small RTD elements – that can withstand 600°C temperatures and heavy vibrations – into the 4.5mm wide mineral-insulated cable and then connecting them. So Danfoss used its extensive knowledge of temperature measurement and production processes to create a patented defocused laser soldering process that can connect four soldering points in one operation. Using PT1000 thin film technology instead of PT100, the new sensor eliminates the need for wire compensation and gives a higher measurement resolution – ideal for measuring the lower RTD temperature points on an engine. The result: A temperature sensor made to cope with heavy vibrations thanks to its unique design. Currently undergoing field tests, the new sensor is expected to be introduced in 2010.