Getting Timestamp from Multiple Devices

Question

I am using LV
8.0 with the Compact DAQ Chassis and NI 6221 (for the encoder input – because the
C DAQ system currently does not have any modules for quadrature counter input).
I have modules NI 9205 and 9237. I will be doing multiple measurements at the
same time (but not simultaneously). The test will last roughly 30 seconds, and
in that time frame I will be receiving signals from:
1) Encoder (for angular position and RPM) (NI 6221 ctr
input)
2) Load Cells, Torque Sensor, (NI 9237)
3) Multiple pressure transducers (NI 9205)
I would like all these modules to operate concurrently, but
not be slowed down by other modules (Continuous buffered acquisition?). What
would be the best way to record and save the data to file with some kind of
timestamp, so that I know at x degrees (using the NI 6221) the force on the
load cell was y (using NI 9237)?
I have tried using the express data acquisition VI but it
doesn’t allow me to use two different cards. And if I have two different
express VI’s, all my data is saved in two different files, but I have no idea which
data point in one file corresponds to which data point in another file in time.
Example: I look at the encoder file, and see that at 0.5
seconds the angle was 30 degrees. If I knew the time at which each data point
was taken, I could do some easy interpolation of the force file to figure out
what the force should have been at time 0.5…
Relative Time                          Force
0.42         
                                    27
0.50         
0.61                                        30

Answer 1

Hi Johnny,
Since you do not need your measurements to be simultaneous, you can use two DAQ Assistants - one for each device.  You can then use merge signals as shown in the below picture and save them to file using Write to Measurement File Express VI.  The header of the file that is created will tell you the intial timestamp and delta t for each data set, so you will know the timing information. 
I think this is the simplest solution to what you are trying to do.  Let us know if there is something about it that doesn't work out for you.
Regards,
Laura
Message Edited by Laura F. on 08-01-2006 03:43 PM
Attachments:
2DAQAsst.jpg ‏15 KB