CDK's tempsensor

[baeckmo]

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.

[CDK]

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.

[baeckmo]

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

[CDK]

Originally Posted by baeckmo

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.

[Fanie]

What is the max temperature that you want to measure ?

[baeckmo]

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.

[Fanie]

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.

[baeckmo]

Originally Posted by Fanie

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.

[Fanie]

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.