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Archiver

Guys,

There were a lot of messages on our forums about temperature measurements.
The existing Dallas, NI and Maxim ICs do a great job with 1-wire,
Temp-to-voltage and digital ICs for most of the jobs.
However, some of us have to work with a very delicate temperature
measurement and control where fast response is everything. Unfortunately
until recently that was a problem, because all these ICs, even the smallest
ones have two crucial limitations -

1. Since the IC itself is a sensor, it has to be attached to some surface
where the measurement takes place. Its easy if all you have to do is to
measure how warm your motherboard is. But try to attach and IC to a polished
silver heated plate for instance. And how the hell would you connect it?

2. The ICs (even the smallest type like microMAXIM packages) are made of
epoxy and are not too good a heat conductors. So in delicate fast
applications the response time may be not acceptable.

So those of us who had to use small thin-film RTDs, thermocouples and
thermistors had to do some analog magic if we wanted to use micros for these
jobs.

Not any more!
I just got great news from MAXIM - two new exciting products that would make
a fast-response temp measurements a snap. I am talking about MAX6674/MAX6675
and MAX6682/MAX6691. Some of the info you can find on their web site, some
have not yet made it there!
The first pair - MAX6674/MAX6675 are thermocouple-to-digital ICs.
MAX6674 converts voltage from a K-thermocouple (0degC to 128degC)to
temperature and store it in 10 bit digital word (0.125degC resolution)and
which you can access at any time via SPI interface.
MAX6675 - 12 bit resolution across 0degC to 1024degC (0.25degC resolution)

The second pair does the same with NTC thermistors (MAX6691 can handle 4 at
a time) . Maxim does it quite smartly by using low duty cycle and low-bias
voltage, which helps to minimize self-heating. Resolution is 10 bit
over -55degC to 125degC.

You can use these with thin-film and super-miniature sensors and get
unbelievable response time and precision. Have fun!
I know I will.
I also have a suspicion that they will have an IC for an RTD in no time too!

Cheers,

Alex Chaihorsky

Archiver

>MAX6674 converts voltage from a K-thermocouple (0degC to 128degC)to
>temperature and store it in 10 bit digital word (0.125degC resolution)and
>which you can access at any time via SPI interface.
>MAX6675 - 12 bit resolution across 0degC to 1024degC (0.25degC resolution)

Hi Alex,

It looks great, except I wish it could go below freezing of good ol'
H2O. I jumped and ordered samples last week when Mike DeMetz
mentioned it here.

The MAX6682 does not come up on the maxim-ic website. Is that a
future product, one channel or something?

-- Tracy

Archiver

> >MAX6674 converts voltage from a K-thermocouple (0degC to
128degC)to
> >temperature and store it in 10 bit digital word
(0.125degC resolution)and
> >which you can access at any time via SPI interface.
> >MAX6675 - 12 bit resolution across 0degC to 1024degC
(0.25degC resolution)

Does anyone know how fast these chips really are? I can't
seem to find any information on the minimum conversion time
.

Archiver

Actually in the guide they list 6682 as existing and 6691
as "future". However, 6691 is in their database and you can oreder
samples, while 6682 disappeared into oblivion without a trace.
Go figure.

Cheers,

Alex.


--- In basicstamps@y..., Tracy Allen <tracy@e...> wrote:
> >MAX6674 converts voltage from a K-thermocouple (0degC to 128degC)to
> >temperature and store it in 10 bit digital word (0.125degC
resolution)and
> >which you can access at any time via SPI interface.
> >MAX6675 - 12 bit resolution across 0degC to 1024degC (0.25degC
resolution)
>
> Hi Alex,
>
> It looks great, except I wish it could go below freezing of good
ol'
> H2O. I jumped and ordered samples last week when Mike DeMetz
> mentioned it here.
>
> The MAX6682 does not come up on the maxim-ic website. Is that a
> future product, one channel or something?
>
> -- Tracy

Archiver

Hi, Michael,

MAXIM documentation states the following conversion times:

MAX6674 min - typical 0.15s maximun 0.18 sec.

MAX6691 min 80ms, typical 100ms, maximum 156ms.

I do not know why they use seconds in one case and milliseconds in
another, so I report, you decide. [noparse]:)[/noparse]

Cheers,

Alex.

---

--- In basicstamps@y..., "R. Michael O'Bannon, Ph.D." <mob@m...>
wrote:
> > >MAX6674 converts voltage from a K-thermocouple (0degC to
> 128degC)to
> > >temperature and store it in 10 bit digital word
> (0.125degC resolution)and
> > >which you can access at any time via SPI interface.
> > >MAX6675 - 12 bit resolution across 0degC to 1024degC
> (0.25degC resolution)
>
> Does anyone know how fast these chips really are? I can't
> seem to find any information on the minimum conversion time
> .