Hello Nok,
Let me explain first how your RTD measures temperature and then I will talk about how the software displays the temperature.
An RTD is a Resistive-Temperature-Detector. It looks like you have platinum RTD which has a nominal resistance of 100Ohms at 0 degrees Celsius. As the temperature of the RTD changes, so does its resistance. The SCXI-1121 has excitation that is used to pass a constant current through your RTD. You can choose to excite your RTD with 0.15mA of current. This 0.15mA current will pass through the RTD. As the resistance of the RTD changes due to a change in temperature, the voltage across the RTD will change, but the current passing through the RTD will remain constant at 0.15mA. Therefore, if you were to measure the voltage ac
ross the RTD at 0 degrees Celsius, your RTD would have a resistance of 100Ohms which yields: 0.15mA*100Ohms = 15mV
You do not have to do any dividing in software, because the hardware knows to divide by the value of the gain you have applied.
In order to get this voltage to be accurately converted to a temperature, I recommend that you use a Virtual Channel. This will allow you to configure the excitation and parameters for your RTD and will also return the measurement in degrees rather than volts. To create a virtual channel, open Measurement and Automation and then right-click on the Data Neighborhood folder and select Create New...
Here is a link to a tutorial with more information and links: http://zone.ni.com/devzone/conceptd.nsf/webmain/D9BAA2AA872A6B5F86256D730079E3E6?opendocument
Regards,
Bill B.
Applications Engineer
National Instruments
