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1  Using Arduino / Sensors / Re: LM35 accuracy on: July 01, 2011, 09:05:24 am
Assuming that the original question was answered ... or not ...
Does anybody know, where I could purchase a TSiC 506 TO92 in Germany/Europe? Seems to be some kind of white elephant, because 206 and 306 I can get from an electronics shop nearby, but 506 (at least TO92) seems to be on shelf almost nowhere, though (afaik) it shouldn't be a TOO expensive chip (10-15€?). And with an accuracy of +-0.1 and digital output that would probably the easiest way to calibrate cheaper sensors.


I thought about a medical thermometer, but the problem is the range. How to get a stable temp of 35-40 degrees (except in my ... smiley-wink )? I ASSume that I wouldn't like that kid of calibration procedure ...
2  Using Arduino / Sensors / Re: LM35 accuracy on: June 30, 2011, 04:18:46 pm
Quote
Don't confuse resolution with accuracy.
Be assured: I don't!
It was just an example bc some seem to think, that I'm looking for some kind of ultra-accuracy solution for 10 ct. No I don't. I simply want to know:
If I have two sensors (which sense whatever) and the manufacturer of these sensors "guarantees" an accuracy of +-0.5 (at a certain range of whatever) and I get a readig of 20 resp 21, can I then assume that the "true" value is around 20.5 - maybe +-0.1 (0.2, more?)?
3  Using Arduino / Sensors / Re: LM35 accuracy on: June 30, 2011, 03:07:43 pm
Nice sayings. Don't help much, but nice anyway.

Having a reading of 20.5 actually/usually means that the temperature is somewhere between 20 and 21. I am not expecting to have an accurate reading of 20.4532°, but getting 20.5 and knowing it's somewhere between 20.4 and 20.7 would be nice sometimes. At least when it can be done more or less cheap.
4  Using Arduino / Sensors / Re: LM35 accuracy on: June 30, 2011, 09:37:03 am
Quote
If accuracy is that important to you,
As said: ACTUALLY I'm not in need for such high accuracy. The question just occured, when I noticed that 2 out of 3 LM35 I purchased seemed to offer a cheap way to increase accuracy (if I should ever need it, that means).

temp reference: That's the problem. Do you know about any "cheap" (say < 20 US$/€) reference thermometer (accuracy better than +-0.2)? Which leads back to my initial question: Would 2 (groups) LM35 (os DS18S20) which deliver results that are 1° (or more) apart be a more or less reliable reference?
5  Using Arduino / Sensors / Re: LM35 accuracy on: June 30, 2011, 08:48:18 am
ok, say I'm using DS18S20 instead ... the "problem" remains smiley-wink

Say, I have ONE that measures 20.5° when then true temp is 20 - the DS18S20 is inaccurate at the same level as the LM35. Means, that I have to live with the inaccuracy. Say, I get a second one and that one measures 20.4°. Doesn't help me much, does it?

But if I, out of pure luck, get two and one measures 19.5 and the other 20.5, how sure could I be that the true temp is something like 20 +- less than 0.5 ?


BTW: can somebody tell me why DS18S22 is more expensive that DS18S20, though the 20 is MORE accurate? 22 offers 12 bit conversion, but what does this help if the inaccuracy is larger anyway?
6  Using Arduino / Sensors / LM35 accuracy on: June 30, 2011, 04:29:18 am
Hi,

I just started playing around with Arduino and try to get things together for a kind of home automation project.
I connected three LM35 to my Arduino and got it all working - fine.

Now:
The three sensors all read different values - I'm not surprised smiley-wink
But:
For example they read: 26.2, 26.5 and 27.2

The "guaranteed" accuracy of the LM35 is +-0.5°. Does this mean, that I can get a quite GOOD value (depending on ref. voltage, circuit quality etc) if I can find 2 LM35 which deliver results that are far apart? Would a "very" accurate value be the average of the two sensors in THIS case?
Or ist this just plain nonsense, and +-1 is the best I could get anyway with such cheap setup?

I do not really care for the current project, because I only have to distinguish between very cold, cold, medium, hot and very hot - more or less smiley-wink
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