[time-nuts] Temperature sensors and quartz crystals (was: HP5061B Versus HP5071 Cesium Line Frequencies)

Attila Kinali attila at kinali.ch
Mon Jun 5 07:30:13 EDT 2017

On Mon, 5 Jun 2017 01:18:59 +0100
Adrian Godwin <artgodwin at gmail.com> wrote:

> Where do digital sensors (e.g. ds1820 and some more recent parts from TI)
> fit into this ?

AFAIK, these are all band-gap temperature sensors. But unlike a discrete
sensor, you have the problem that they only contain a low resolution
ADC on die (somewhere between 8 and 14 bit). If your goal is to measure
temperature and report it with an accuracy of about 1°C, then these are
the easiest to use sensors you can buy. Sensor noise doesn't really matter
with them, as it is dominated by the low ADC resolution. I don't have any
long term stability data on those, but given their use-case I do not think
that they are very stable. Although long term stability might not be an
issue at all, again due to low ADC resolution.

If you need better precision, accuracy, or stability, then choosing one
of the modern delta-sigma ADCs that directly support thermistors
(e.g. like AD7124) is not much more difficult, though a bit more expensive
(around 10USD instead of 5USD like for an TMP107). Additionally you need
to calbirate the system, which means you need a reference temperature sensor
and a setup with which you can produce different temperatures. Though for
an oven kind of temperature control, one can live without calibration.

				Attila Kinali
You know, the very powerful and the very stupid have one thing in common.
They don't alters their views to fit the facts, they alter the facts to
fit the views, which can be uncomfortable if you happen to be one of the
facts that needs altering.  -- The Doctor

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