Author Topic: NTC as 1000 °C sensor?  (Read 1919 times)

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Online firewalkerTopic starter

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NTC as 1000 °C sensor?
« 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.

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.

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Offline ogden

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Re: NTC as 1000 °C sensor?
« Reply #1 on: December 17, 2019, 03:09:37 pm »
 
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Online Kleinstein

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Re: NTC as 1000 °C sensor?
« Reply #2 on: December 17, 2019, 05:19:02 pm »
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.
 
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Offline thermistor-guy

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Re: NTC as 1000 °C sensor?
« Reply #3 on: December 18, 2019, 02:36:33 am »
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.

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
 
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Online Gyro

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Re: NTC as 1000 °C sensor?
« Reply #4 on: December 18, 2019, 09:20:34 am »
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?
Best Regards, Chris
 
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Online firewalkerTopic starter

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Re: NTC as 1000 °C sensor?
« Reply #5 on: December 18, 2019, 09:25:35 am »
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?

This is the "normal" for EGT sensors in cars. Tungsten or Platinum RTDs. Also N-type thermocouples are used (mainly as after market solutions). It was the first time I came across an NTC.
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Offline Nauris

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Re: NTC as 1000 °C sensor?
« Reply #6 on: December 18, 2019, 04:35:47 pm »
Many ceramics and glasses start to be conductive at that sort of temperatures, it is certainly possible to make NTC-temp sensor if one selects a suitable one. I can imagine for example piece of silicon carbide working fine in this application.
 
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Offline rvalente

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Re: NTC as 1000 °C sensor?
« Reply #7 on: December 19, 2019, 09:49:08 am »
This catalog has some information on characteristics for egt sensors

https://www.mte-thomson.com.br/wp-content/uploads/2019/09/13th-Edition-EGTS-MTE-THOMSON.pdf
 
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