Oh that's not what I did... This was down a probe and I wanted to save wires so one end was tied to the probe case (ground). And I just ignored the voltage drop of the current along ground.
It sounds like you subtracted the lead wire resistance.
Well the bridge can get rid of some of the DC offset. So he (the OP) would only be looking at the changes in resistance. He'd could get more out of his limited bits. (I realize you know all this, so that last bit (NPI) was directed at the OP.)
George H.
Basically subtract twice the resistance of *one* wire and call it a day.
absolute temperature using a RTD pt1000 sensor with short lead wires (
precision of +/-0.1 C, but after reading some posts in this group I'll settle for the best I can get.
pt100(0) are simple voltage divider, constant current driving and bridge. For my needs, it seems like a voltage divider, eventually polarized from a precision reference, and a buffer amplifier will do the trick, but i'm not sure i'm not missing something.
First off why are you not interested in the rather significant advantages of 4-terminal (Kelvin clips) measurement?
Second why only 12 bits? 16 bits will gain you a lot performance wise.
Finally, how are you dealing with calibration? 0.1 degrees C is readily achievable but requires calibration.
?-)
solute temperature using a RTD pt1000 sensor with short lead wires (
cision of +/-0.1 C, but after reading some posts in this group I'll settle for the best I can get.
t100(0) are simple voltage divider, constant current driving and bridge. Fo r my needs, it seems like a voltage divider, eventually polarized from a pr ecision reference, and a buffer amplifier will do the trick, but i'm not su re i'm not missing something.
he's using pt1000 and
I'm guessing that is what the MCU he's using has on chip
-Lasse
I'm happier with a well-stirred crushed-ice-water bath - the water has to be kept moving through the ice, and spinning magnet stirrer seems to work fine.
It's good to close to couple of millidegrees Kelvin.
-- Bill Sloman, Sydney
es
Exactly Lasse, more precisely AWG23 is 0.067 ohm/m, so well below 0.1C
Exact again Lasse!
Josephkk, in fact I'm using a TI launchpad with a ARM Cortex uP. This is a one-off design to be used in a research environment. Using the evaluation b oard saves me the effort of designing the digital part of the project (I ho pe!). On the other hand 12 bit with a voltage span of 3.3 V gives me a reso lution of 0.8 mV or, with a 170C of temp spam, a 0.04C resolution. So, if I can keep all the errors of the analog part below the 0.8mV threshold I'll be OK with 12 bits, but if I can't (most probably) I don't see the advantag e of using more bits unless I use an all digital solution.... right?
yI have no idea but i think I'll go with Bill's solution. The BIPM's publica tion "TECHNIQUES FOR APPROXIMATING THE INTERNATIONAL TEMPERATURE SCALE OF 1
990" might also be helpful.Regards
Mariano
Oversample and average to improve the resolution. You can even add a little analog noise, which will improve the DNL of the ADC. One way to get the noise is to stream random bits out a parallel port pin and RC lowpass filter.
The uP on-chip ADCs tend to be mediocre.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation
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