Has anyone seen lag when using a DAQPad-6015?

[phartwell]

I have been using a DAQCARD-6062e and just got a DAQPAD-6015. <br><br>I am using these to continuously collect samples from a sensor. Using two copies of the same VI in Labview 7.1 on XP, I can start 2 tasks, one for each device. I am monitoring the output of 2 sensors, one on each device, at the same time. I am sampling 10 channels of AI at 3kS/s. The DAQPAD is 16bit, the DAQCARD is 12 bit.<br><br>The signals start out synchronized. But if I let the application run for about 5 minutes, there is a lag on the DAQPAD relative to the DAQCARD. This lag can be from 2 to 4 seconds! I am not missing any data from the DAQPAD, its just showing up late. I am sure it is not in my VI programming since it works fine with the DAQCARD.<br><br>It this just what I should expect for a USB based DAQ system relative to my PCMCIA based DAQCARD?<br>Since this is a new product, perhaps there are driver improvements pending to increase the performance?<br><br>Anyone got any ideas??<br><br>Thanks,<br><br>pete.

[sergesl]

Hello Phartwell <br><br>The delay you are having is due to time drift between the two devices. Each device has an internal timebase from which it derives its sample clock. Since the two time bases are not synchronized and the sample clock derivation process is proper to each device, there is a drift between the two acquisition processes. The drift is very small and that is why you cannot notice it at the beginning. But once you let the programs run for a long time, the drift increases and becomes noticeable.<br><br>To avoid this, you can synchronize both operations by sharing a sample clock for example. That way, you are sure that they will acquire always at the same time. For example, you could route the sample clock of one device to be used as the sample clock of the other device using a PFI line. If you use LabVIEW, there are shipping examples that deal with DAQmx synchronization. If you are programing in Traditional NI-DAQ, you can search our developper exchange for examples. <br><br>Hope this helps. Have a good weekend.