temperature control with labview arduino and a thermistor

[giladd]

Hello
i want to use a thermistor with my arduino uno to find out what is the temperature
i see that there is a vi for this but,my thermistor is RTD pt100 so i dont know how the change the VI because the temp calc is different for every kind of thermistor

thank you,

Gilad

[Nathan_B.]

You simply need to determine the Steinhart-Hart equation coefficients and then change them in the thermistor VI.  I found a cool calculator for thermistors (but I don't know it's correctness).

[hrh1818]

A platinum RTD resistance changes approximately 0.0039 ohms/ohm/degree Celsius. For the exact value see:

<http://en.wikipedia.org/wiki/Resistance_thermometer#R_vs_T_relationship_of_various_metals>  and

<http://en.wikipedia.org/wiki/Resistance_thermometer#Standard_resistance_thermometer_data>

To avoid self heating an excitation current of 1 milliamp is used.  For a 100 ohm platinum RTD you will get a 0.39 millivolt change in output for a 1 degree Celsius change in temperature.  The Arduino Uno's ADC least significant bit is 5 millivolts.  Hence if you have a fixed requirement to use a 100 ohm Platinum RTD you will need to amplify the output signal to obtain a measurement resolution better than 10 degree Celsius.

Or you could use a 1000 ohm platinum RTD.  This link shows the simplest RTD signal conditioner I found when searching the Internet.   Notice the signal conditioner is for a 1000 ohm Platinum RTD.

hrh1818