Hi there.
I hate to interrupt on someone else's thread but...
You probably can't know the temperature of your sensor very well with that
method. But it sounds like you weren't trying to calibrate the sensor, you
were just testing the circuit to see if it worked.
Still, the actual temperature of your DS18B20 may be far different than the
temperature of your other probe.
The probe on the multimeter may be more or less reflective than the IC in
question. The more "black" of the two sensors will get much hotter due to
absorbing more of the IR radiation from the iron. Even sitting in the sun,
if the IC is in a black plastic case and the probe on your multimeter is in
a nice, shiny, stainless steel probe then I'd expect to see a great
difference between the two. The IC being much hotter. The same would hold
true when using the IR radiation from the soldering iron.
If the IC gets above 125 C, it may act funny but I doubt that you're
getting it that hot from what you've described so this shouldn't cause the
IC to stop working, it just might be at a far different temperature than
you believe it to be.
We often use a stirred water or oil bath to attempt to get our sensors to
the same temperature as the reference thermometer when performing
calibrations. But this requires that the sensors be mounted in
waterproof/oilproof housings (thermally conductive of course) and that you
have a way to control or at least know the water or oil bath temp too.
You can rig something up fairly cheap to do the job, actually.
I've never played with the DS18B20s before so I can't comment much about
them or why they seem to be failing in your application.
Good luck
Jim
At 11:16 AM 2/22/2004 +1100, you wrote:
>Using the analyser would be even easier than counting cycles but I need to
>go and borrow it from someone. I'll check the lib as suggested and see if I
>can easily tell there.
>
>As for the question re temperature testing methods, I was very
>unscientific, I have a temp probe on the multimeter for comparison and I
>use the radiated (not touching) heat from my soldering station set to <100c
>as a heat source. I had the same problem with earlier tests sitting the
>18b20 outside in the sun so I don't think it's my heat source that is the
>problem.
>
>
>At 10:46 AM 22/02/2004, you wrote:
>>I wrote code for the '1820 - found that they are reliable with clock pulse
>>widths some 20% wider than Dallas suggests.
>
>
>