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### Topic: Measuring the resistance and thus temperature of an RTD (Read 1 time)previous topic - next topic

#### Voidugu

##### May 06, 2013, 09:54 am
I have a soldering pencil which has an integrated PTC RTD built in. The temperature of the RTD can be represented using this equation y = 0.0056x^2+4.9382X-239.43 where x is the resistance of the RTD and y is the temperature in Celsius. The resistance would vary from 50 to 100 ohms (its a relatively low resistance for an RTD).

Could you please provide me with a way to measure the resistance of the RTD giving the greatest resolution to the arduino measuring it? (ie use all 1024 voltage levels measured with the arduino's analogRead() )

#### Magician

#1
##### May 06, 2013, 01:31 pm
You would not get much better resolution, if you 'd carefully scale input  to 0-5 range using OPA,  compare to simple R - RTD voltage divider.
Other options,  use external ADC, 16 - 24 bits, or you may dig for Atmel app. note explaining oversampling technics AVR121.
For update rate 3 Hz , which is (IMHO) o'k with temperature measurements, they give this numbers:
Quote

Voltage        Oversa-       Right      Ideal           Ideal voltage           Maximum
resolution     mpled      shifted decimated      representation         Bandwidth
result

~75 uV       4096X         6X        32413             2.4729V               ~3Hz (1)

#### Voidugu

#2
##### May 06, 2013, 02:37 pm
Magician could you please explain to me the term OPA and the table you posted below?
Thanx again

#### Magician

#3
##### May 06, 2013, 03:26 pm
Table from AVR121, google for it. OPA - operational amplifier: http://en.wikipedia.org/wiki/Operational_amplifier

#### Voidugu

#4
##### May 07, 2013, 08:11 am
Thanks for the help magician

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