How to retrieve the temperature by a Pt100 (2 threads ) with NI myDAQ with an external circuit?

[hamdouch1000]

hi everybody my supervisor requires me not to use the ohm meter to the NI myDAQ and he ask me to create an external circuit in order that I may accquire data using the map and the circuit I want to know the contents of this circuit and the appropriate VI!! help please 

[TBirkulosis]

Here is an example of how to Measure Temperature using an RTD, myDAQ, and LabVIEW. It looks like the PT100 is an RTD, correct?

Additionally, LabVIEW comes with a built-in example for temperature measurements. It can be found in Help > Find Examples. Then select Hardware Input and Output > DAQmx > Analog Input. There is an example called 'RTD or Thermoresistor - Continuous Input.vi'. This can also be a good starting point.

The basic steps in LabVIEW are DAQmx Create Channel (select AI Temperature RTD), set up DAQmx Timing (if needed), Start Task, Read (put in while loop for continuous samples), Stop Task, Clear Task.

[hamdouch1000]

thank you so much it was very good point to start but i need a circuit with some resistance i want just to know if mydaq can give me an external source because i used to get out the voltage U=RI so what should i do exactally ?

[TBirkulosis]

Just for clarification, this is not about an external power source, correct? Are you building a circuit to measure the analog output or input of the myDAQ?

[hamdouch1000]

yes it's a circuit to measure analog output because i have to determine the resistance and convert it on °C using the table of convertion 

[Kristoff2]

The most basic way to measure a variable resistance using an anlog input is a voltage divider: http://en.wikipedia.org/wiki/Voltage_divider

The use the variable resistance (the PT100 in this case) as R1 in the image in the link above.  When the resistance of R1is huge R2 is insignificant and your analog input will read ~0.  When the resistsance of R1 is tiny the analog input will read ~Vcc.

Then just use the equations to convert the analog voltage to resistance and then resistance to temperature with the equations from the specific device you're using.

Let us know if that makes sense.

-Sam K

LabVIEW Hacker

Join / Follow the LabVIEW Hacker Group on google+