[time-nuts] Any experienced HP 2804A thermometer users outthere?

Didier didier at cox.net
Sat Jan 24 21:24:09 UTC 2009


I have never used the 1-wire sensor, but I have actually used Thermochrons
recorders from Dallas Semi, I still have some in equipment, and I have one
in my car at the moment :-)

But there are cases where there are too big, or they are in a noisy
environment, and a thermistor is more flexible. 

Another advantage of the thermistor is the low overhead to make a reading.
On most ucontrollers, the ADC runs under interrupts, so it does not take
much resources to make a reading. It's only if you want to convert the
reading in degrees that you have to run a linearization routine. For low
precision needs, I just use an 8 bit lookup table. That gives precision
better than a degree C around 25 C with very little CPU time. It's plenty
for things like thermal protection or temperature compensation.

The 18B20 is almost as small as a thermistor, but I do not have code for it.
Can't be too hard though.

Thanks for the pointer,

Didier

> -----Original Message-----
> From: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Poul-Henning Kamp
> Sent: Saturday, January 24, 2009 1:48 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Any experienced HP 2804A thermometer 
> users outthere?
> 
> In message <CD547DCFF6D34F198AF32525FEC677B6 at didierhp>, 
> "Didier" writes:
> 
> For permanent measurement points, I prefer the Dallas DS18B20 
> 1-wire sensors, they interface to a single I/O pin on 
> anything programmable and gives 1/160C resolution and +/- 
> .50C precision.
> 
> -- 
> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> phk at FreeBSD.ORG         | TCP/IP since RFC 956
> FreeBSD committer       | BSD since 4.3-tahoe    
> Never attribute to malice what can adequately be explained by 
> incompetence.
> 
> 




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