[time-nuts] uC ADC resolution (was: Poor man's oven)
logan.cummings at gmail.com
Wed Jun 7 23:55:06 EDT 2017
This discussion of temperature measurement with ADCs has crossed into my
professional life and without being too much of a commercial plug just
wanted to mention that I support Linear Technology's temp-to-bits family of
ICs: LTC2983, LTC2984, LTC2986.
Overview: each part has 3 24-bit delta-sigma ADCs along with low leakage
input buffers, excitation sources, an internal mux, and a small
linearization engine. They can measure just about any type of temperature
sensor and digitize it to deg C or F with really good accuracy. Ultimately
accuracy will depend on the sensor, your implementation, environmental
conditions, etc. but the parts have a lot of features that help you get the
most out of a given sensor.
They aren't super cheap (Digi-Key pricing is particularly bad, if you
can order from Linear direct it's much better) but they are to my knowledge
by far the simplest way to interface to a thermistor, RTD, thermocouple,
etc. and get <1degC accuracy.
Ping me off-list if you want to know more or have an application question
On Wed, Jun 7, 2017 at 8:04 PM, jimlux <jimlux at earthlink.net> wrote:
> On 6/7/17 7:35 PM, Bob kb8tq wrote:
>> Metal actually makes things a bit worse since it has a lower thermal
>> resistance than glass.
>> This is also why a high performance dewar is made from glass rather than
>> metal. Yes, you
>> can go to weird stuff like titanium (it has been done). You can’t afford
>> that ….
>> If you fill the entire dewar with a heat conductor you make things worse
>> still. The idea is to
>> *block* heat flow out of the heated area. Even without fill, the wall of
>> the dewar goes from the outside
>> world to the heart of the heated area. It is the perfect “sneak" path
>> into the oven. Actually
>> it’s not that much of a sneak path since it’s a well known effect :)
>> Again, none of this is particularly original. Take a hammer to any dewar
>> based OCXO and
>> the details are going to be similar.
> And the wires provide a thermal path - you've got to get power to it and
> the oscillator signal out.
> In dewar OCXOs (like the USOs made by APL), the leads are essentially the
> only thermal path in/out.
> BTW, you don't want to do oil filled. All oil filled electronics (unless
> welded closed) inevitably leaks, oozes, or otherwise puts oil on the
> outside. If you *must* have oil, then use solid, uninsulated wires to
> penetrate the surface of the oil. Otherwise you'll gain new appreciation
> for what capillary action is.
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