NI PCI 6143 + Labview

[NBChaaben]

To measure simultaneously three AC voltages , we have chosenas the NI PCI 6143. we wan to mesure the rms
voltage  AC: 8.4mV + -7%.
 
 
We succeeded to measure the the rms voltage of this signal in one chanel (task) but we have encountered two problems for multithreading in action:
- The second measures is slightly lagged when using the same measurment VI (the VI attached);
- An error message appears when using independent measurement VIs (C_à_d for each channel AI0, Ai1 and Ai2 we are used an independent Vi);

Thank you for helping me to find the source of these error messages as well as multithreading.
 
See attached the VI of analog measurement

[lmtis]

Create a DAQmx task that samples multiple channels.

You did not post your error message, but it could be from multiple VIs trying to communicate with the module simultaneously.  You can't do that.