Am using a PCI-7340 to control a drive for a motor (drill spindle) with no feedback on one axis, so have the axis disabled and am using the DAC output to set specific voltages. With the analog cable to the drive disconnected, I can set voltages and the DAC output reads correctly and is stable. But when connected to the drive, the voltage drops., For instance setting 2.5V results in 1.95V (but is 2.5V when the cable is disconnected). Setting 10V output yields 7.75V, not the max that I need. The input impediance of the drive is specified as >50k, and I measured it at 114 kohms. The Specs of the 7340 say it can provide 5 mA, and with a load of 114 k that is well within its range.
Also leaving the DAC output fixed, the drive frequency slowly increases over time, but not consistently - probably just heating up, but the voltage does change slightly over time as well, even though the DAC output command has not changed.
It seems like a loading issue, yet with an input impedance of 114k how can this be?
It isn't electrical noise in the machine as the voltage I get is consistently less than what I set, and is not too unstable, about +-50 mV fluctuation (more variability than I want to control the drive).
Any ideas?