High Temperature Thermistors or RTD's

[peterlow]

I am trying to find what is available in high temperature thermistors or RTD's. I have read in some literature (10 Reed's Marine Engineering Series - Instrumentation and Control Systems) that through special compositions thermistors can be made to detect ranges up to 1600ºC. For my application I would be looking for a device that can handle continuous operation at 1100-1200ºC with excursions up to 1300-1400ºC. I am having difficulty finding anything remotely close to this and was wondering if anyone has any idea if something like this exists. I'd prefer a thermistor or RTD as they are the more common use is automotive applications. I know thermocouples can measure this but would prefer not to use one. Thanks in advance for any help you can give.

 

[itsmoked]

Boy... ! The RTD tables only go to 850C!! You want to almost double that? RTDs are based on their mechanical shape for accuracy. Putting them in a position where their substrate is forced over a 1000C realm is a big problem.

This is as close as I think you will find:

http://www.dwmai.com/bodylow-new.html

Thermistors are usually made via a sintering process... Heating them to those temperatures will no doubt screw with the whole design.

Better start thinking creatively about T/Cs.. They are so cheap and 1200C is idling along balmy for them.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[cbarn24050]

platinum alloy thermocouple is what you need to use.

 

[ScottyUK]

cbarn is correct, one of the platinum alloy thermocouples would be an excellent choice.

http://instserv.com/rmocoupl.htm

Why are you biased against t/c's? They are used in high temperature service in much tougher environments than anything automotive could ever imagine - heavy process, petrochem, power generation, steel production... the key is buying good quality thermocouples from reliable suppliers. Signal conditioning for t/c's isn't remotely challenging for modern electronics - I wouldn't worry too much about the interfacing.


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Sometimes I only open my mouth to swap feet...

 

[peterlow]

Thanks for the info guys. My reasons for wanting to stay away from thermocouples is purely on the basis that you just don't see them in production model cars, at least to my knowledge. I don't know if this is based on them not being able to stand up to certain conditions or just after awhile people got used to using a certain sensor and adopted it as industry standard. If someone can prove me wrong and say that thermocouples are used in production model vehicles then by all means I would welcome it and want to know what thermocouple manufacturer is providing this.

 

[itsmoked]

The reason is because RTDs are more linear, can be hooked up with copper wire, and worked at the lower temps needed.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[JimCasey]

This could only be exhaust gas. What sensors are used for aircraft EGT sensors?

 

[DaveScott]

I think you have to be careful with type R and S, apart from the higher cost. They need to be put in a ceramic tube. They won't like vibration much.
Type K is by far the most common, and would be your best bet for a slightly oxidising atmosphere up to about 1250C.

What is your application?

 

[ScottyUK]

And type K won't appreciate excursions to 1400 [°]C, which was the reason for discounting it.

EGTs are typically much lower temperature than that - most turbines are quite happy with type K for EGT measurement. I wonder if military aircraft measure afterburner EGT?


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Sometimes I only open my mouth to swap feet...

 

[peterlow]

The atompshere that the temperature sensing device would be both a reducing and oxidising environment. Currently on our test rig we use R type thermocouples for measuring the high temp regions but as you said before, they won't like vibration much.
The application is an aftertreatment device for exhaust systems.

 

[DaveScott]

Peter, what sort of error could you tolerate, and what time response do you need?

 

[ScottyUK]

These might be of interest.

http://www.accutru.com/ExLCCover.pdf

Have you considered any of the non-contact methods such as optical pyrometry or one of the emerging technologies such as laser-absorption radiation thermometry (LART)?

What service life do you need, and what conditions will the sensor be exposed to? Is this a laboratory automotive test rig, or something which will be fitted to a vehicle and see the rough and tumble of an outdoor environment with vibration and shock / impact hazards?



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Sometimes I only open my mouth to swap feet...