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.
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.
Please contact your nearest Danfoss supplier to learn more about our extensive product portfolio and how we can help you.
By Christian Dall Larsen, Market and Application Manager