Temperature Sensors

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MTV<=>Operator
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Temperature Sensors

Post by MTV<=>Operator » November 30th, 2019, 3:20 pm

I have a couple of questions about temperature sensors used in this event.
1. Are we restricted to using the temperature sensors under the "legal" list or are those just some examples of legal sensors? (I assumed they were just some examples)
2. Would a TI-LM35 be legal?
3. Is a temperature sensor that comes with a linear voltage to temperature formula preferred over one with a non-linear voltage to temperature formula? (Given that we have to create a linear relationship between voltage and temperature in water, I would think that a sensor that already has a linear relationship between voltage and temperature in air would be better)
4. Is there any particular sensor that is more accurate than others?

Thanks in advance
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Re: Temperature Sensors

Post by YeagerTheCat » November 30th, 2019, 7:34 pm

MTV<=>Operator wrote: I have a couple of questions about temperature sensors used in this event.
1. Are we restricted to using the temperature sensors under the "legal" list or are those just some examples of legal sensors? (I assumed they were just some examples)
2. Would a TI-LM35 be legal?
3. Is a temperature sensor that comes with a linear voltage to temperature formula preferred over one with a non-linear voltage to temperature formula? (Given that we have to create a linear relationship between voltage and temperature in water, I would think that a sensor that already has a linear relationship between voltage and temperature in air would be better)
4. Is there any particular sensor that is more accurate than others?

Thanks in advance
I think they are trying to get you to use a basic analog sensor, one that isn't doing all the work for you. If it is analog (not digital) voltage or something that changes in resistance (say a thermistor) then you are likely ok. LM35 seems to fit that bill just fine.
None of them are perfectly linear but clearly some of them are harder to model than others. The preference is all yours :-)
In respect to accuracy, yes indeed, the datasheet for any of the analog ones will tell you what their out of the box accuracy is. One should be careful about what this means though (eg: relative accuracy in respect to what).

YtC

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Re: Temperature Sensors

Post by jinhusong » December 1st, 2019, 10:36 am

The LM35, TMP36 are all legit, but they are not easy either. Their output depends on the noise of the power input (USB to the computer, i2c to the lcd display all effects it). The output range is not in the sweet range of built-in ADC. Somehow, after play with them, we decided to go with thermistor. Still, no show stopper for them, it is still doable, especially the op-amp chips are allowed on a breadboard.

Jinhu

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