Which temperature sensor do you choose?

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I want to make a simple temperature sensing a drum filled with water, I just want to measure the air temperature inside the drum. The temperature range from 0 Celcius to 120 Celcius. The sensor option is PT100, and LM35. Which one do you choose for linearity?
Thanks

KISS - Keep It Simple Stupid!

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So which is it???

Do you want to measure the water temperature, or the air temperature?

Quote:

...make a simple temperature sensing a drum filled with water, I just want to measure the air temperature inside the drum.

With a jacketed PT100 (expensive) you can immerse the probe directly in the liquid. That would be hard to do with an LM35 - unless it was water proofed real well.

You can avoid reality, for a while.  But you can't avoid the consequences of reality! - C.W. Livingston

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Carl,
the water is heated and cooled. But i only need to know the air temperature above the water inside the drum. The sensor are fixed at the topmost of the drum and water level never touched the sensor. I don't care about the price :twisted:. If I use LM35 i can just apply glue gun onto the cable terminals to protect it from moisture.

KISS - Keep It Simple Stupid!

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Then the LM35 it is... That would be my choice for this application - as long as you can keep it dry.

But then too, you might want to look at the data-sheet, your wanting to measure up to 120 degrees C. I don't know if the LM35 can go above 100 degrees C.

You need to check it out in the data-sheet - before you make your decision...

Otherwise, you might want to consider a Thermistor. Very cheap! And if you can live with a range that is only say, 30 to 50 degrees C, you might get be able to key in on a linear part of the devices temperature curve. Otherwise, you'll need to use a look-up table to get the needed linearity.

You can avoid reality, for a while.  But you can't avoid the consequences of reality! - C.W. Livingston

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I would avoid Pt100 if possible. NTC would be my first choice if temp range allows for it. Otherwise, LM35 is also as good as another.

Guillem.
"Common sense is the least common of the senses" Anonymous.

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Note, also, that a big blob of hot glue on the sensor will significantly slow its thermal response, in case that matters.

Getting a good seal without embedding the entire sensor is difficult, in practice. Covering the entire sensor gives a much better seal, but it takes a while to equilbrate to the ambient temp.

JC

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If you dont care about the price, I would suggest to add the sensirion, SHT series to the poll.
Digital output, no calibration, quit accurate and you get humidity also. And it works.

( not connected to them, just a satisfied user)

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I used SHT75 earlier as well. Really good product, but the price is almost the same as a PT100. PT100 is also a lot more accurate.

There has been some problems with the SHT sensor if the air has been blown near it.

You can buy PT100s cheaper as well if you do not need to stick to a Lab accuracy.

It is not hard to use it as you will only need a constant current source and an instrumentation / Diff. Amp. for the input stage.

After proper scaling of the input signal the 10 bit ADC of an AVR could be also used for signal digitalization. Although 16 bit ADCs are also not expensive.

Regards,

Peter

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Thanks for all of your answer!
I've looked at SHT75, it's a good choice :D very good accuracy but as due date coming closer i had to choose quickly between those two (PT100 vs LM35). Though i still confuse which one i will use, i've made my board compatible to receive those 2 sensors. :D
Again thanks 4 you all.

KISS - Keep It Simple Stupid!