[time-nuts] What do people use for measuring temperature?

[Manfred Bartz]

A thermistor should do the job.  You can buy them in SMD packages and
down to 0.1% accuracy.
How much resolution you get depends on the measurement range and the
ADC you are using.

A platinum RTD would be another candidate but requires more signal
conditioning.
In 3-wire or 4-wire probe configuration you can compensate for long probe wires.

Any sensor you choose should have a thermal mass less that the item
you want to measure.
Generally, a smaller sensor means smaller thermal mass.

If you really need to resolve 0.01ºC or 0.001ºC then you also need to
pay attention to:
 * sensor self-heating
 * consider turning off excitation between measurements
 * with a thermistor, go with a high R25,  i.e. 100kΩ which will help
with keeping self-heating low.
 * Temperature coefficient and environment of the thermistor's series resistor.
 * Stability of the supply/reference voltage.

BTW, 0.1% resistors are sensitive to static discharge. A zap can
easily produce a 0.5% change!

Having really good and stable thermal contact is essential.
The item you are measuring and the sensor should be in an isolated
micro environment.
Airflow or proximity to anything of a different temperature will
potentially cause a temperature gradient between sensor and the
measured item.

All passive temperature sensors require some sort of linearization,
but that could be done away from the sensor or during post-processing.
For thermistors search for the "Steinhart Hart equation".

I am not aware of active (smart) sensors with have better than 0.1ºC
resolution, but I also have not done any significant search lately.

Cheers
--
Manfred VK3AES

On Sat, Sep 26, 2020 at 12:46 PM Hal Murray <hmurray at megapathdsl.net> wrote:
>
>
> I've got a collection of 1-wire gizmos and USB thumb drives.  They are great
> for many applications but I'm looking for something better/different.
>
> I'd like something that reads to 0.01 degree or 0.001 degree.  I don't need
> accuracy.  What I want is reasonable linearity so I can make pretty graphs.
>
> I'd like the actual probe to be small enough so I can poke it inside gear like
> a PC and attach it to a crystal.
>
> I'm looking for a USB or serial connection so I can log the data.
>
> Is there an obvious brand/whatever I should be looking at? thermistor?
> thermocouple?  ...
>
> I don't care about a display on the device.  I don't want a logger, they fill
> up.  I want to grab the data on the fly and do my own logging.  (But I'm happy
> to use a logger if it will do what I want.)
>
>
> --
> These are my opinions.  I hate spam.
>
>
>
>
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-- 
Manfred  VK3AES