Difference between NTC. PT 100 & thermocouples

[smpsmp45]

We have seen various types of probes being used for temp sensing. What is the basic difference & what applications is suited best for each of these?

[Tesla]

Hi smpsmp45
NTC means Negative Temperature Coefficient = when the temp rises the resistance drops - common for thermister type sensors used in BMS in Ausi.
PT 100 = Platinum RTD (Resistance Temperature Detector) used for a temp range of 0C to 100C. These sensors are reliable, linnier and have optimal characteristics over a wide range. They have a PTC (Positive Temp Coefficient). material = noble.
Thermocouples are basicly two dissimilar mettals where at the junction (join) of the metals (wire) a voltage is created which changes with temp. These sensors are used for accuracy at mainly high temps up to about 2500C.
To summarise - sensor types
Thermister = room temp, water temp
RTD = room temp, water temp
Thermocouple = high temp
-characteristics
NTC
PTC

[Peter_1]

An not to to forget, the resistance of a PT100 = 100 ohm at 0°C.

You also have PT1000 (1000 ohms at 0°C)
They made a PT1000 because it's less prone to cable resistance.
Many PT100 or PT1000's have 3 wires to calculate the resistance of the wires between probe and display to compensate this difference automatically.

Thermocouple use also if you need a fast response of the temperature.

If you need accuracy at 0.1°C, use PT100 or PT1000 (=expensive), otherwise PTC and NTC is the sensor for almost any HVAC/R application (=cheap)

[smpsmp45]

That is very good response. Many thanks

[narkom]

[quote=Peter_1;82494]An not to to forget, the resistance of a PT100 = 100 ohm at 0°C.

You also have PT1000 (1000 ohms at 0°C)
quote]

Are you sure of it?
I guess 1000 ohms at 25C...

[Peter_1]

http://www.elektrorevue.cz/clanky/05021/image048.png

[Peter_1]

http://www.buerkert.de/img_article/PT100_18d.jpg

[narkom]

OK!
But I told about PTC and NTC thermistors.The rated resistance Rr is the resistance value at temperature Tr that is 25C, unless otherwise specified. In the refrigeration field we often have NTC thermistors with 10kOhm at 25C and PTC thermistors with 1kOhm at 25C
Regards!

[Peter_1]

So, I was sure.

[smpsmp45]

I also came to know that With PT 100, the only error which can take place is sensor cable broken. But with Thermocouples one can land is big problems if they go faulty. The control mechanism with thermocoules may not work & can make the compressor run all the time.