CDK's tempsensor

In the thread on DIY tunnel drives CDK used a sensor for measuring turbine-housing temperature. How does it function, what kind of readout signal does it generate, what...... . Unfortunately, when it comes to solid state devices, I just came out of the cave, so please explain to me in a language understood by non-electronicists.

 

That is an extremely simple device: a small piece of semiconductor material with a positive temp coefficient (resistance increases with temperature), encapsulated in an epoxy transistor package (to-92) with only 2 leads.
The chip is directly under the flat side of the package so it's easy to obtain a good thermal contact.

The mother of all these devices is the Siemens KTY-10.
Compared to the cheaper NTC's used for thermostats, the accuracy is an order of magnitude better (up to 1%). The max. temperature is 180 C., not because the device cannot handle more but because the linearity isn't guaranteed beyond that point.

To use a KTY-xxx all you need to do is measure the resistance with a multimeter and look up the temperature in the graph.

 

Clear enough, thanks! Would you dare say what the "technical" max temp might be?

 

It is a generally accepted fact that at 270 C. an irreversible degradation starts. That was certainly the case with old-fashioned semiconductor casings containing oxygen, but any chip is regarded with distrust, even if it survived 270 C. without noticeable electric parameter changes.

 

What is the max temperature that you want to measure ?

 

Well, actually there are a couple of applications, where improved technology would be needed, for instance:

1) A simple warning for high temp in watercooled exhausts (=low cooling water flow) is required for some operations. CDK's chip could do fine with a simple LED or acoustic alarm, trigging on a limiting voltage (?)

2) The exhaust temp is a very good indicator on engine loading and condition. Here we have temp's in the 400 to 650 C range. New cheaper/more reliable tech? (This is for you CDK, in order to twist your fuel settings equally on both engines!).

3) Low thermal mass interesting for some industrial measurements.

 

For water temperature up to around 130 deg C you could also look at the LM35 temp sensor, it's output is linear.

For tempratures as high as 400 deg + one would probably have to use a thermo couple, type K is probably going to be the most common. You will need to amplify the signal, the TC output is in mV.

 

Yup, that's what we have today.

 

I would stick to it, simply for it's reliability and durabilty, not that other sensors are not usable, there are some, but the TC's are hard to beat. The type K outputs a relative large mV and can be amplified easily.

Although not 100% linear, it is close enough for general purpose ie temperature indication if one or two degrees out won't matter.