Thermistor vs Thermocouple

[Excom]

Hallo

I am going to make a micro-calorimeter and in this micro-calorimeter I need a very sensitive temperature sensor. I think I am going to use a thermistor or a thermopile. But which one to choose?

With which temperature sensor do I get the highest sensitivity? And with which temperature sensor can I make the fastest temperature measurements?

I hope that someone can help.

Thanks in advance.

 

[vk6kro]

You could use either of those, but you should look at the other options first.

For example there is a chip called an 18B20 which can measure temperature to 1/16th of a degree. They come already calibrated. They cost about US$5 but need to be read with a microprocessor like a Picaxe.

They can take several readings each second, but the body of the device (which looks like a low powered transistor) would take a several seconds to acquire the temperature from its surroundings.
If suddenly plunged into hot water from cold, it might take 15 seconds or more to come to temperature.

Another chip is the LM35.
These give 10 mV out per degree celcius from -55 to 150 deg C.
Digikey have them for $6.55

I haven't done a detailed search, so there are probably better chips out there.

 

[Ravaner]

Hi. I'm not a great specialist of these subjects, but I use to work with thermistor and I must precise at least to main items :

1) if you use thermistor and need a precise and fast response you must choose "glass beads" thermistor (not so easy to find for an amateur).

2 ) Temperature modify the internal resistance of this component according to a mathematic law including exponential and so you need to digitize the resistance (voltage in fact) and process mathematically this data. I do that but I use a microcontroller.

As it has been told, LM35 is a very good choice, low cost and easy to use.

 

[dlgoff]

I am going to make a micro-calorimeter...

What temperatures are you expecting? And what accuracy?
I would recommend using a Platinum RTD (Resistance Temperature Detector) for good range and accuracy.
http://www.omega.com/prodinfo/rtd.html"

 

[Mike_In_Plano]

RTDs are generally your most accurate option, while thermistors are your most sensitive. In either case, you have some degree of self heating. (NTC) Thermistors are non linear, but they've always been my favorite for sensitivity.

 

[Excom]

Hi

Thanks for the answers.

I am going to fabricate the thermocouple or thermistor by my self. It is only import that the temperature sensor is very sensitive around 310 K (37 ºC). The temperature sensor must reach sensitivity around 20 µK or less.

 

[0xDEADBEEF]

Maybe it would help if you could tell us why you cannot just buy a micro calorimeter. I guess there are a few more parameters, like a corrosive environment or fields or such things involved, this will determine much more what might be suitable.
Can you calibrate the sensor yourself? How do you control your heat bath? How fast do you really need to be?