All four DAC channels on my 7344 have an unwanted DC offset of approx -0.14V in the output.

[Phil Nasser]

All four DAC channels on my 7344 have an unwanted DC offset of approx -0.14V in the output. This occurs when I implement the "D/A Load sub VI" in one of my VI's (i'm using Flexmotion v5.1.1 with LabVIEW 6.0). I configured all axes so that the DAC channels are unmapped. I also disconnected everything else from the UMI 7764 (except wire leads from DAC terminals to my DMM). I even tried to apply various resistive loads (1K-1M ohm) to the outputs. When I boot up my PC and initialize the 7344 board, the outputs read 0V. However, from the first time that I issue any value to the D/A Load VI, the offset appears and stays. The offset value varies slightly, from around -0.15 to -0.
13V.

[Brent_R]

Phil,

This offset is normal for the 7344. The D/A outputs are not calibrated and normally do not need to be, since the onboard control loop automatically compensates for any errors during servo moves. As you have noticed, the offset should be fairly constant across the full command range. Compensating for this error in software usually works very well.

Regards,

Brent R.
Applications Engineer
National Instruments

[Jochen]

Phil,

just to make it clearer: The analog outputs of the 7344 are not intended to be used as general purpose outputs. The purpose is to use them as outputs in a motion control loop and in this case an offset really doesn't matter as Brent explained.

Jochen Klier
AE Group Leader
National Instruments Germany