Electronics > Projects, Designs, and Technical Stuff
NTC as 1000 °C sensor?
firewalker:
Yesterday I had to test an automotive EGT (Exhaust Gas Temperature) sensor. Every time I had to test such a sensor it was an RTD type or a Thermocouple.
In this case it was a ~150k NTC thermistor. It was behaving as an NTC to be more exact. Negative coefficient and sensitive. The temperatures in the exhaust are almost 1000 °C.
Later I confirmed it is a thermistor.
I was under the impression that an NTC can;t go that high without being damaged. Is it a special type of thermistor?
Alexander.
ogden:
There are various types of thermistors:
https://www.shibauraelectronics.com/documents/en/products/SD_product_catalog_en_201601.pdf
Kleinstein:
How temperature stable the sensor is depends on the material. With the usually large change in resistance with NTCs it usually needs different materials for different ranges anyway. At high temperature that could be the problem that isolation becomes difficult, so one does not like high resistance sensors at high temperature.
thermistor-guy:
--- Quote from: firewalker on December 17, 2019, 02:46:14 pm ---Yesterday I had to test an automotive EGT (Exhaust Gas Temperature) sensor. Every time I had to test such a sensor it was an RTD type or a Thermocouple.
In this case it was a ~150k NTC thermistor. It was behaving as an NTC to be more exact. Negative coefficient and sensitive. The temperatures in the exhaust are almost 1000 °C.
...
I was under the impression that an NTC can;t go that high without being damaged. Is it a special type of thermistor?
Alexander.
--- End quote ---
That high a temperature rating is unusual. Glass-encapsulated chip thermistors rated at 300 deg. C are readily available: https://sensing.honeywell.com/135-103FAG-J01-thermistors
Some Silicon-based devices are rated at 500 deg. C: http://www.adsem.com/gpage1.html
Research on diamond-based thermistors, apparently stable to 880 deg. C under cycling: https://ieeexplore.ieee.org/document/8695127
Gyro:
Tungsten has a reasonable temperature coefficient (positive), just a bit higher than Platinum.
Maybe you could make use of Tungsten wire on a ceramic former - or even a halogen bulb with quartz envelope?
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